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Sample records for periodic mass extinctions

  1. Periodic Comet Showers, Mass Extinctions, and the Galaxy

    NASA Technical Reports Server (NTRS)

    Rampino, M. R.; Stothers, R. B.

    2000-01-01

    Geologic data on mass extinctions of life and evidence of large impacts on the Earth are thus far consistent with a quasi-periodic modulation of the flux of Oort cloud comets. Impacts of large comets and asteroids are capable of causing mass extinction of species, and the records of large impact craters and mass show a correlation. Impacts and extinctions display periods in the range of approximately 31 +/- 5 m.y., depending on dating methods, published time scales, length of record, and number of events analyzed. Statistical studies show that observed differences in the formal periodicity of extinctions and craters are to be expected, taking into consideration problems in dating and the likelihood that both records would be mixtures of periodic and random events. These results could be explained by quasi-periodic showers of Oort Cloud comets with a similar cycle. The best candidate for a pacemaker for comet showers is the Sun's vertical oscillation through the plane of the Galaxy, with a half-period over the last 250 million years in the same range. We originally suggested that the probability of encounters with molecular clouds that could perturb the Oort comet cloud and cause comet showers is modulated by the Sun's vertical motion through the galactic disk. Tidal forces produced by the overall gravitational field of the Galaxy can also cause perturbations of cometary orbits. Since these forces vary with the changing position of the solar system in the Galaxy, they provide a mechanism for the periodic variation in the flux of Oort cloud comets into the inner solar system. The cycle time and degree of modulation depend critically on the mass distribution in the galactic disk. Additional information is contained in the original extended abstract.

  2. Periodic mass extinctions and the Planet X model reconsidered

    NASA Astrophysics Data System (ADS)

    Whitmire, Daniel P.

    2016-01-01

    The 27 Myr period in the fossil extinction record has been confirmed in modern data bases dating back 500 Myr, which is twice the time interval of the original analysis from 30 years ago. The surprising regularity of this period has been used to reject the Nemesis model. A second model based on the Sun's vertical Galactic oscillations has been challenged on the basis of an inconsistency in period and phasing. The third astronomical model originally proposed to explain the periodicity is the Planet X model in which the period is associated with the perihelion precession of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated to mass extinctions, a trans-Neptunian super-Earth planet has been proposed to explain the observation that the inner Oort cloud objects Sedna and 2012VP113 have perihelia that lie near the ecliptic plane. In this Letter, we reconsider the Planet X model in light of the confluence of the modern palaeontological and outer Solar system dynamical evidence.

  3. Structure and dating errors in the geologic time scale and periodicity in mass extinctions

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1989-01-01

    Structure in the geologic time scale reflects a partly paleontological origin. As a result, ages of Cenozoic and Mesozoic stage boundaries exhibit a weak 28-Myr periodicity that is similar to the strong 26-Myr periodicity detected in mass extinctions of marine life by Raup and Sepkoski. Radiometric dating errors in the geologic time scale, to which the mass extinctions are stratigraphically tied, do not necessarily lessen the likelihood of a significant periodicity in mass extinctions, but do spread the acceptable values of the period over the range 25-27 Myr for the Harland et al. time scale or 25-30 Myr for the DNAG time scale. If the Odin time scale is adopted, acceptable periods fall between 24 and 33 Myr, but are not robust against dating errors. Some indirect evidence from independently-dated flood-basalt volcanic horizons tends to favor the Odin time scale.

  4. Periodicity of extinction: A 1988 update

    NASA Technical Reports Server (NTRS)

    Sepkowski, J. John, Jr.

    1988-01-01

    The hypothesis that events of mass extinction recur periodically at approximately 26 my intervals is an empirical claim based on analysis of data from the fossil record. The hypothesis has become closely linked with catastrophism because several events in the periodic series are associated with evidence of extraterrestrial impacts, and terrestrial forcing mechanisms with long, periodic recurrences are not easily conceived. Astronomical mechanisms that have been hypothesized include undetected solar companions and solar oscillation about the galactic plane, which induce comet showers and result in impacts on Earth at regular intervals. Because these mechanisms are speculative, they have been the subject of considerable controversy, as has the hypothesis of periodicity of extinction. In response to criticisms and uncertainties, a data base was developed on times of extinction of marine animal genera. A time series is given and analyzed with 49 sample points for the per-genus extinction rate from the Late Permian to the Recent. An unexpected pattern in the data is the uniformity of magnitude of many of the periodic extinction events. Observations suggest that the sequence of extinction events might be the result of two sets of mechanisms: a periodic forcing that normally induces only moderate amounts of extinction, and independent incidents or catastrophes that, when coincident with the periodic forcing, amplify its signal and produce major-mass extinctions.

  5. Extended period of K/T boundary mass extinction in the marine realm

    NASA Technical Reports Server (NTRS)

    Keller, G.

    1988-01-01

    The Cretaceous/Tertiary (K/T) boundary mass extinction has been widely recognized as a nearly instantaneous catastrophy among marine plankton such as foraminifera. However, the suddenness of this extinction event may have been overemphasized because most pelagic K/T boundary sequences are stratigraphically incomplete and generally lack the earliest Tertiary (Zones P0 and P1a) either due to carbonate dissolution and/or non-deposition. Stratigraphically complete sections appear to be restricted to continental shelf regions with high sedimentation rates and deposition well above the CCD. Such sections have been recovered from El Kef, Tunisia (1) and Brazos River, Texas. Quantitative foraminiferal analysis of these sections indicate an extinction pattern beginning below the K/T boundary and ending above the boundary. These data imply that the mass extinction event was not geologically instantaneous, but occurred over an extended period of time. Evidence supporting this conclusion is discussed.

  6. Mass Extinctions Past and Present.

    ERIC Educational Resources Information Center

    Allmon, Warren Douglas

    1987-01-01

    Discusses some parallels that seem to exist between mass extinction recognizable in the geologic record and the impending extinction of a significant proportion of the earth's species due largely to tropical deforestation. Describes some recent theories of causal factors and periodicities in mass extinction. (Author/TW)

  7. Mass extinction: a commentary

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1987-01-01

    Four neocatastrophist claims about mass extinction are currently being debated; they are that: 1, the late Cretaceous mass extinction was caused by large body impact; 2, as many as five other major extinctions were caused by impact; 3, the timing of extinction events since the Permian is uniformly periodic; and 4, the ages of impact craters on Earth are also periodic and in phase with the extinctions. Although strongly interconnected the four claims are independent in the sense that none depends on the others. Evidence for a link between impact and extinction is strong but still needs more confirmation through bed-by-bed and laboratory studies. An important area for future research is the question of whether extinction is a continuous process, with the rate increasing at times of mass extinctions, or whether it is episodic at all scales. If the latter is shown to be generally true, then species are at risk of extinction only rarely during their existence and catastrophism, in the sense of isolated events of extreme stress, is indicated. This is line of reasoning can only be considered an hypothesis for testing. In a larger context, paleontologists may benefit from a research strategy that looks to known Solar System and Galactic phenomena for predictions about environmental effects on earth. The recent success in the recognition of Milankovitch Cycles in the late Pleistocene record is an example of the potential of this research area.

  8. Periodicity of mass extinctions without an extraterrestrial cause.

    PubMed

    Lipowski, Adam

    2005-05-01

    We study a lattice model of a multispecies prey-predator system. Numerical results show that for a small mutation rate the model develops irregular long-period oscillatory behavior with sizeable changes in a number of species. The periodicity of extinctions on Earth was suggested by Raup and Sepkoski [Proc. Natl. Acad. Sci. 81, 801 (1984)], but thus far is lacking a satisfactory explanation. Our model indicates that this might be a natural consequence of the ecosystem dynamics and not the result of any extraterrestrial cause.

  9. The end-Permian mass extinction: A complex, multicausal extinction

    NASA Technical Reports Server (NTRS)

    Erwin, D. H.

    1994-01-01

    The end-Permian mass extinction was the most extensive in the history of life and remains one of the most complex. Understanding its causes is particularly important because it anchors the putative 26-m.y. pattern of periodic extinction. However, there is no good evidence for an impact and this extinction appears to be more complex than others, involving at least three phases. The first began with the onset of a marine regression during the Late Permian and resulting elimination of most marine basins, reduction in habitat area, and increased climatic instability; the first pulse of tetrapod extinctions occurred in South Africa at this time. The second phase involved increased regression in many areas (although apparently not in South China) and heightened climatic instability and environmental degradation. Release of gas hydrates, oxidation of marine carbon, and the eruption of the Siberian flood basalts occurred during this phase. The final phase of the extinction episode began with the earliest Triassic marine regression and destruction of nearshore continental habitats. Some evidence suggests oceanic anoxia may have developed during the final phase of the extinction, although it appears to have been insufficient to the sole cause of the extinction.

  10. Limits to biodiversity cycles from a unified model of mass-extinction events

    NASA Astrophysics Data System (ADS)

    Feulner, Georg

    2011-04-01

    Episodes of species mass extinction dramatically affected the evolution of life on Earth, but their causes remain a source of debate. Even more controversy surrounds the hypothesis of periodicity in the fossil record, with conflicting views still being published in the scientific literature, often even based on the same state-of-the-art datasets. From an empirical point of view, limitations of the currently available data on extinctions and possible causes remain an important issue. From a theoretical point of view, it is likely that a focus on single extinction causes and strong periodic forcings has strongly contributed to this controversy. Here I show that if there is a periodic extinction signal at all, it is much more likely to result from a combination of a comparatively weak periodic cause and various random factors. Tests of this unified model of mass extinctions on the available data show that the model is formally better than a model with random extinction causes only. However, the contribution of the periodic component is small compared to factors such as impacts or volcanic eruptions.

  11. Mass extinctions in the deep sea

    NASA Technical Reports Server (NTRS)

    Thomas, E.

    1988-01-01

    The character of mass extinctions can be assessed by studying extinction patterns of organisms, the fabric of the extinction, and assessing the environmental niche and mode of life of survivors. Deep-sea benthic foraminifera have been listed as little affected by the Cretaceous-Tertiary (K-T) mass extinction, but very few quantitative data are available. New data on deep-sea Late Maestrichtian-Eocene benthic foraminifera from Maud Rise (Antractica) indicate that about 10 percent of the species living at depths of 2000 to 2500 m had last appearances within 1 my of the Cretaceous-Tertiary (K-T) boundary, versus about 25 percent of species at 1000 to 1500 m. Many survivors from the Cretaceous became extinct in a period of global deep-sea benthic foraminiferal extinction at the end of the Paleocene, a time otherwise marked by very few extinctions. Preliminary conclusions suggest that the deep oceanic environment is essentially decoupled from the shallow marine and terrestrial environment, and that even major disturbances of one of these will not greatly affect the other. This gives deep-sea benthic faunas a good opportunity to recolonize shallow environments from greater depths and vice versa after massive extinctions. The decoupling means that data on deep-sea benthic boundary was caused by the environmental effects of asteriod impact or excessive volcanism. The benthic foraminiferal data strongly suggest, however, that the environmental results were strongest at the Earth's surface, and that there was no major disturbance of the deep ocean; this pattern might result both from excessive volcanism and from an impact on land.

  12. Periodicity in marine extinction events

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. John, Jr.; Raup, David M.

    1986-01-01

    The periodicity of extinction events is examined in detail. In particular, the temporal distribution of specific, identifiable extinction events is analyzed. The nature and limitations of the data base on the global fossil record is discussed in order to establish limits of resolution in statistical analyses. Peaks in extinction intensity which appear to differ significantly from background levels are considered, and new analyses of the temporal distribution of these peaks are presented. Finally, some possible causes of periodicity and of interdependence among extinction events over the last quarter billion years of earth history are examined.

  13. Mass extinctions and missing matter

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.

    1984-01-01

    The possible influence of 'invisible matter' on the solar system's comet halo, and therefore on quasi-periodic cometary bombardment of the earth and consequent mass extinctions, is briefly addressed. Invisible matter consisting of small or cold interstellar molecular clouds could significantly modulate the comet background flux, while invisible matter consisting of a large population of old, dead stars with a relatively small galactic concentration probably could not. It is also shown that the downward force exerted by the Galaxy will perturb the halo, but will not produce any periodicity.

  14. Mass extinction efficiency and extinction hygroscopicity of ambient PM2.5 in urban China.

    PubMed

    Cheng, Zhen; Ma, Xin; He, Yujie; Jiang, Jingkun; Wang, Xiaoliang; Wang, Yungang; Sheng, Li; Hu, Jiangkai; Yan, Naiqiang

    2017-07-01

    The ambient PM 2.5 pollution problem in China has drawn substantial international attentions. The mass extinction efficiency (MEE) and hygroscopicity factor (f(RH)) of PM 2.5 can be readily applied to study the impacts on atmospheric visibility and climate. The few previous investigations in China only reported results from pilot studies and are lack of spatial representativeness. In this study, hourly average ambient PM 2.5 mass concentration, relative humidity, and atmospheric visibility data from China national air quality and meteorological monitoring networks were retrieved and analyzed. It includes 24 major Chinese cities from nine city-clusters with the period of October 2013 to September 2014. Annual average extinction coefficient in urban China was 759.3±258.3Mm -1 , mainly caused by dry PM 2.5 (305.8.2±131.0Mm -1 ) and its hygroscopicity (414.6±188.1Mm -1 ). High extinction coefficient values were resulted from both high ambient PM 2.5 concentration (68.5±21.7µg/m 3 ) and high relative humidity (69.7±8.6%). The PM 2.5 mass extinction efficiency varied from 2.87 to 6.64m 2 /g with an average of 4.40±0.84m 2 /g. The average extinction hygroscopic factor f(RH=80%) was 2.63±0.45. The levels of PM 2.5 mass extinction efficiency and hygroscopic factor in China were in comparable range with those found in developed countries in spite of the significant diversities among all 24 cities. Our findings help to establish quantitative relationship between ambient extinction coefficient (visual range) and PM 2.5 & relative humidity. It will reduce the uncertainty of extinction coefficient estimation of ambient PM 2.5 in urban China which is essential for the research of haze pollution and climate radiative forcing. Copyright © 2017 Elsevier Inc. All rights reserved.

  15. The end-triassic mass extinction event

    NASA Technical Reports Server (NTRS)

    Hallam, A.

    1988-01-01

    The end-Triassic is the least studied of the five major episodes of mass extinction recognized in the Phanerozoic, and the Triassic-Jurassic boundary is not precisely defined in most parts of the world, with a paucity of good marine sections and an insufficiency of biostratigraphically valuable fossils. Despite these limitations it is clear that there was a significant episode of mass extinction, affecting many groups, in the Late Norian and the existing facts are consistent with it having taken place at the very end of the period. The best record globally comes from marine strata. There was an almost complete turnover of ammonites across the T-J boundary, with perhaps no more than one genus surviving. About half the bivalve genera and most of the species went extinct, as did many archaeogastropods. Many Paleozoic-dominant brachiopods also disappeared, as did the last of the conodonts. There was a major collapse and disappearance of the Alpine calcareous sponge. Among terrestrial biota, a significant extinction event involving tetrapods was recognized. With regard to possible environmental events that may be postulated to account for the extinctions, there is no evidence of any significant global change of climate at this time. The existence of the large Manicouagan crater in Quebec, dated as about late or end-Triassic, has led to the suggestion that an impact event might be implicated, but so far despite intensive search no unequivocal iridium anomaly or shocked quartz was discovered. On the other hand there is strong evidence for significant marine regression in many parts of the world. It is proposed therefore that the likeliest cause of the marine extinctions is severe reduction in habitat area caused either by regression of epicontinental seas, subsequent widespread anoxia during the succeeding transgression, or a combination of the two.

  16. The biology of mass extinction: a palaeontological view

    NASA Technical Reports Server (NTRS)

    Jablonski, D.; Raup, D. M. (Principal Investigator)

    1989-01-01

    Extinctions are not biologically random: certain taxa or functional/ecological groups are more extinction-prone than others. Analysis of molluscan survivorship patterns for the end-Cretaceous mass extinctions suggests that some traits that tend to confer extinction resistance during times of normal ('background') levels of extinction are ineffectual during mass extinction. For genera, high species-richness and possession of widespread individual species imparted extinction-resistance during background times but not during the mass extinction, when overall distribution of the genus was an important factor. Reanalysis of Hoffman's (1986) data (Neues Jb. Geol. Palaont. Abh. 172, 219) on European bivalves, and preliminary analysis of a new northern European data set, reveals a similar change in survivorship rules, as do data scattered among other taxa and extinction events. Thus taxa and adaptations can be lost not because they were poorly adapted by the standards of the background processes that constitute the bulk of geological time, but because they lacked--or were not linked to--the organismic, species-level or clade-level traits favoured under mass-extinction conditions. Mass extinctions can break the hegemony of species-rich, well-adapted clades and thereby permit radiation of taxa that had previously been minor faunal elements; no net increase in the adaptation of the biota need ensue. Although some large-scale evolutionary trends transcend mass extinctions, post extinction evolutionary pathways are often channelled in directions not predictable from evolutionary patters during background times.

  17. Impact Crises, Mass Extinctions, and Galactic Dynamics: A Unified Theory

    NASA Technical Reports Server (NTRS)

    Rampino, M.R.

    1997-01-01

    recovery and radiation of new taxa. Isotopic and other geochemical signatures are also generally consistent with the expected after-effects of catastrophic impacts. Seven of the recognized extinction pulses are associated with concurrent (in some cases multiple) stratigraphic impact markers (e.g., layers with high Ir, shocked minerals, microtektites), and/or large, dated impact craters. Other less-well-studied crisis intervals show elevated Ir, still well below that of the K/T spike, which might be explained by low-Ir impactors, ejecta blowoff, or the sedimentary reworking and dilution of impact signatures. The best explanation for a possible periodic component of about 30 m.y. in mass extinctions and clusters of impacts is the modulation of the comet flux associated with the solar system's periodic passage through the plane of the Milky Way Galaxy. The quantitative agreement among paleontological, geological, and astronomical data suggests an important underlying unification of the processes involved.

  18. Climate modelling of mass-extinction events: a review

    NASA Astrophysics Data System (ADS)

    Feulner, Georg

    2009-07-01

    Despite tremendous interest in the topic and decades of research, the origins of the major losses of biodiversity in the history of life on Earth remain elusive. A variety of possible causes for these mass-extinction events have been investigated, including impacts of asteroids or comets, large-scale volcanic eruptions, effects from changes in the distribution of continents caused by plate tectonics, and biological factors, to name but a few. Many of these suggested drivers involve or indeed require changes of Earth's climate, which then affect the biosphere of our planet, causing a global reduction in the diversity of biological species. It can be argued, therefore, that a detailed understanding of these climatic variations and their effects on ecosystems are prerequisites for a solution to the enigma of biological extinctions. Apart from investigations of the paleoclimate data of the time periods of mass extinctions, climate-modelling experiments should be able to shed some light on these dramatic events. Somewhat surprisingly, however, only a few comprehensive modelling studies of the climate changes associated with extinction events have been undertaken. These studies will be reviewed in this paper. Furthermore, the role of modelling in extinction research in general and suggestions for future research are discussed.

  19. The Sixth Great Mass Extinction

    ERIC Educational Resources Information Center

    Wagler, Ron

    2012-01-01

    Five past great mass extinctions have occurred during Earth's history. Humanity is currently in the midst of a sixth, human-induced great mass extinction of plant and animal life (e.g., Alroy 2008; Jackson 2008; Lewis 2006; McDaniel and Borton 2002; Rockstrom et al. 2009; Rohr et al. 2008; Steffen, Crutzen, and McNeill 2007; Thomas et al. 2004;…

  20. Flood basalts and mass extinctions

    NASA Technical Reports Server (NTRS)

    Morgan, W. Jason

    1988-01-01

    There appears to be a correlation between the times of flood basalts and mass-extinction events. There is a correlation of flood basalts and hotspot tracks--flood basalts appear to mark the beginning of a new hotspot. Perhaps there is an initial instability in the mantle that bursts forth as a flood basalt but then becomes a steady trickle that persists for many tens of millions of years. Suppose that flood basalts and not impacts cause the environmental changes that lead to mass-extinctions. This is a very testable hypothesis: it predicts that the ages of the flows should agree exactly with the times of extinctions. The Deccan and K-T ages agree with this hypothesis; An iridium anomaly at extinction boundaries apparently can be explained by a scaled-up eruption of the Hawaiian type; the occurrence of shocked-quartz is more of a problem. However if the flood basalts are all well dated and their ages indeed agree with extinction times, then surely some mechanism to appropriately produce shocked-quartz will be found.

  1. A unified theory of impact crises and mass extinctions: quantitative tests.

    PubMed

    Rampino, M R; Haggerty, B M; Pagano, T C

    1997-05-30

    , and gradual ecological recovery and radiation of new taxa. Isotopic and other geochemical signatures are also generally consistent with the expected after-effects of catastrophic impacts. Seven of the recognized extinction pulses seem to be associated with concurrent (in some cases multiple) stratigraphic impact markers (e.g., layers with high iridium, shocked minerals, microtektites), and/or large, dated impact craters. Other less well-studied crisis intervals show elevated iridium, but well below that of the K/T spike, which might be explained by low-Ir impactors, ejecta blowoff, or sedimentary reworking and dilution of impact signatures. The best explanation for a possible periodic component of approximately 30 Myr in mass extinctions and clusters of impacts is the pulselike modulation of the comet flux associated with the solar system's periodic passage through the plane of the Milky Way Galaxy. The quantitative agreement between paleontologic and astronomical data suggests an important underlying unification of the processes involved.

  2. Life in the Aftermath of Mass Extinctions.

    PubMed

    Hull, Pincelli

    2015-10-05

    The vast majority of species that have ever lived went extinct sometime other than during one of the great mass extinction events. In spite of this, mass extinctions are thought to have outsized effects on the evolutionary history of life. While part of this effect is certainly due to the extinction itself, I here consider how the aftermaths of mass extinctions might contribute to the evolutionary importance of such events. Following the mass loss of taxa from the fossil record are prolonged intervals of ecological upheaval that create a selective regime unique to those times. The pacing and duration of ecosystem change during extinction aftermaths suggests strong ties between the biosphere and geosphere, and a previously undescribed macroevolutionary driver - earth system succession. Earth system succession occurs when global environmental or biotic change, as occurs across extinction boundaries, pushes the biosphere and geosphere out of equilibrium. As species and ecosystems re-evolve in the aftermath, they change global biogeochemical cycles - and in turn, species and ecosystems - over timescales typical of the geosphere, often many thousands to millions of years. Earth system succession provides a general explanation for the pattern and timing of ecological and evolutionary change in the fossil record. Importantly, it also suggests that a speed limit might exist for the pace of global biotic change after massive disturbance - a limit set by geosphere-biosphere interactions. For mass extinctions, earth system succession may drive the ever-changing ecological stage on which species evolve, restructuring ecosystems and setting long-term evolutionary trajectories as they do. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. Testing for periodicity of extinction

    NASA Technical Reports Server (NTRS)

    Raup, David M.; Sepkoski, J. J., Jr.

    1988-01-01

    The statistical techniques used by Raup and Sepkoski (1984 and 1986) to identify a 26-Myr periodicity in the biological extinction record for the past 250 Myr are reexamined, responding in detail to the criticisms of Stigler and Wagner (1987). It is argued that evaluation of a much larger set of extinction data using a time scale with 51 sampling intervals supports the finding of periodicity. In a reply by Sigler and Wagner, the preference for a 26-Myr period is attributed to a numerical quirk in the Harland et al. (1982) time scale, in which the subinterval boundaries are not linear interpolations between the stage boundaries but have 25-Myr periodicity. It is stressed that the results of the stringent statistical tests imposed do not disprove periodicity but rather indicate that the evidence and analyses presented so far are inadequate.

  4. The Geochemistry of Mass Extinction

    NASA Astrophysics Data System (ADS)

    Kump, L. R.

    2003-12-01

    The course of biological evolution is inextricably linked to that of the environment through an intricate network of feedbacks that span all scales of space and time. Disruptions to the environment have biological consequences, and vice versa. Fossils provide the prima facie evidence for biotic disruptions: catastrophic losses of global biodiversity at various times in the Phanerozoic. However, the forensic evidence for the causes and environmental consequences of these mass extinctions resides primarily in the geochemical composition of sedimentary rocks deposited during the extinction intervals. Thus, advancement in our understanding of mass extinctions requires detailed knowledge obtained from both paleontological and geochemical records.This chapter reviews the state of knowledge concerning the geochemistry of the "big five" extinctions of the Phanerozoic (e.g., Sepkoski, 1993): the Late Ordovician (Hirnantian; 440 Ma), the Late Devonian (an extended or multiple event with its apex at the Frasnian-Famennian (F-F) boundary; 367 Ma), the Permian-Triassic (P-Tr; 251 Ma), the Triassic-Jurassic (Tr-J; 200 Ma), and the Cretaceous-Tertiary (K-T; 65 Ma). The focus on the big five is a matter of convenience, as there is a continuum in extinction rates from "background" to "mass extinction." Although much of the literature on extinctions centers on the causes and extents of biodiversity loss, in recent years paleontologists have begun to focus on recoveries (see, e.g., Hart, 1996; Kirchner and Weil, 2000; Erwin, 2001 and references therein).To the extent that the duration of the recovery interval may reflect a slow relaxation of the environment from perturbation, analysis of the geochemical record of recovery is an integral part of this effort. In interpreting the geochemical and biological records of recovery, we need to maintain a clear distinction among the characteristics of the global biota: their biodiversity (affected by differences in origination and extinction

  5. Mass Extinctions and Biosphere-Geosphere Stability

    NASA Astrophysics Data System (ADS)

    Rothman, Daniel; Bowring, Samuel

    2015-04-01

    Five times in the past 500 million years, mass extinctions have resulted in the loss of greater than three-fourths of living species. Each of these events is associated with significant environmental change recorded in the carbon-isotopic composition of sedimentary rocks. There are also many such environmental events in the geologic record that are not associated with mass extinctions. What makes them different? Two factors appear important: the size of the environmental perturbation, and the time scale over which it occurs. We show that the natural perturbations of Earth's carbon cycle during the past 500 million years exhibit a characteristic rate of change over two orders of magnitude in time scale. This characteristic rate is consistent with the maximum rate that limits quasistatic (i.e., near steady-state) evolution of the carbon cycle. We identify this rate with marginal stability, and show that mass extinctions occur on the fast, unstable side of the stability boundary. These results suggest that the great extinction events of the geologic past, and potentially a "sixth extinction" associated with modern environmental change, are characterized by common mechanisms of instability.

  6. Origination, diversity, and extinction metrics essential for analysis of mass biotic crisis events: An example from cretaceous ammonoidea

    NASA Technical Reports Server (NTRS)

    Collom, Christopher J.

    1988-01-01

    Traditional mass extinction research has predominently concentrated on statistically demonstrating that mass extinction intervals are significantly above background levels of familial and generic extinction in terms of extinction percentage, extinction rate, and per-taxon extinction rate; mass extinction intervals occur on a set periodicity throughout geologic time, which is estimated to be some 30 MYR in duration. The published literature has given little emphasis to equally important considerations and metrics such as origination rate, standing diversity, and rate of generation of new taxa DURING mass extinction intervals. The extent to which a mass extinction affects the regional or global biota, must ultimately be gauged by taking into consideration both the number of taxa which become extinct at or near the event (stage) boundary, and the number of taxa which are either not affected at all by the extinction or actually evolved during or shortly before/after the extinction interval. These effects can be seen in Cretaceous Ammonoidea (at the genus level), and their combined usage allow better insight into paleobiological dynamics and responses to mass extinction and its affect on this dominant Molluscan organism.

  7. Mass Extinctions and Supernova Explosions

    NASA Astrophysics Data System (ADS)

    Korschinek, Gunther

    A nearby supernova (SN) explosion could have negatively influenced life on Earth, maybe even been responsible for mass extinctions. Mass extinction poses a significant extinction of numerous species on Earth, as recorded in the paleontologic, paleoclimatic, and geological record of our planet. Depending on the distance between the Sun and the SN, different types of threats have to be considered, such as ozone depletion on Earth, causing increased exposure to the Sun's ultraviolet radiation or the direct exposure of lethal X-rays. Another indirect effect is cloud formation, induced by cosmic rays in the atmosphere which result in a drop in the Earth's temperature, causing major glaciations of the Earth. The discovery of highly intensive gamma-ray bursts (GRBs), which could be connected to SNe, initiated further discussions on possible life-threatening events in the Earth's history. The probability that GRBs hit the Earth is very low. Nevertheless, a past interaction of Earth with GRBs and/or SNe cannot be excluded and might even have been responsible for past extinction events.

  8. Rapid recovery from the Late Ordovician mass extinction

    NASA Technical Reports Server (NTRS)

    Krug, A. Z.; Patzkowsky, M. E.

    2004-01-01

    Understanding the evolutionary role of mass extinctions requires detailed knowledge of postextinction recoveries. However, most models of recovery hinge on a direct reading of the fossil record, and several recent studies have suggested that the fossil record is especially incomplete for recovery intervals immediately after mass extinctions. Here, we analyze a database of genus occurrences for the paleocontinent of Laurentia to determine the effects of regional processes on recovery and the effects of variations in preservation and sampling intensity on perceived diversity trends and taxonomic rates during the Late Ordovician mass extinction and Early Silurian recovery. After accounting for variation in sampling intensity, we find that marine benthic diversity in Laurentia recovered to preextinction levels within 5 million years, which is nearly 15 million years sooner than suggested by global compilations. The rapid turnover in Laurentia suggests that processes such as immigration may have been particularly important in the recovery of regional ecosystems from environmental perturbations. However, additional regional studies and a global analysis of the Late Ordovician mass extinction that accounts for variations in sampling intensity are necessary to confirm this pattern. Because the record of Phanerozoic mass extinctions and postextinction recoveries may be compromised by variations in preservation and sampling intensity, all should be reevaluated with sampling-standardized analyses if the evolutionary role of mass extinctions is to be fully understood.

  9. Did a Gamma-Ray Burst Initiate the Late Ordovician Mass Extinction?

    NASA Technical Reports Server (NTRS)

    Melott, A. L.; Lieberman, B. S.; Laird, C. M.; Martin, L. D.; Medvedov, M. V.; Thomas, B. C.; Cannizzo, J. K.; Gehrels, N.; Jackman, C. H.

    2004-01-01

    Gamma-ray bursts (hereafter GRB) produce a flux of radiation detectable across the observable Universe. A GRB within our own galaxy could do considerable damage to the Earth's biosphere; rate estimates suggest that a dangerously near GRB should occur on average several times per billion years. At leastfive times in the history of lfe, the Earth experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and GRB may also have contributed. The late Ordovician mass extinction approximately 440 million years ago may be at least partly the result of a GRB. Due to severe depletion of the ozone layer, intense solar ultraviolet radiation is expected to result from a nearby GRB, and some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identijied as the probable cause of this mass extinction, may have resultedfiom a GRB.

  10. Periodic extinction of families and genera

    NASA Technical Reports Server (NTRS)

    Raup, D. M.; Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

    1986-01-01

    Eight major episodes of biological extinction of marine families over the past 250 million years stand significantly above local background (P < 0.05). These events are more pronounced when analyzed at the level of genus, and generic data exhibit additional apparent extinction events in the Aptian (Cretaceous) and Pliocene (Tertiary) Stages. Time-series analysis of these records strongly suggests a 26-million-year periodicity. This conclusion is robust even when adjusted for simultaneous testing of many trial periods. When the time series is limited to the four best-dated events (Cenomanian, Maestrichtian, upper Eocene, and middle Miocene), the hypothesis of randomness is also rejected for the 26-million-year period (P < 0.0002).

  11. Extinctions of life

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

    1988-01-01

    This meeting presentation examines mass extinctions through earth's history. Extinctions are charted for marine families and marine genera. Timing of marine genera extinctions is discussed. Periodicity in extinctions during the Mesozoic and Cenozoic eras is plotted and compared with Paleozoic extinction peaks. The role of extinction in evolution and mankind's role in present extinctions are examined.

  12. Deccan Volcanism, Chicxulub Impact, Climate Change and the end-Cretaceous Mass Extinction

    NASA Astrophysics Data System (ADS)

    Keller, Gerta; Punekar, Jahnavi; Mateo, Paula; Adatte, Thierry; Spangenberg, Jorge

    2015-04-01

    Age control for Deccan volcanism, associated global climate changes, high-stress conditions and the KTB mass extinction is excellent based on biostratigraphy and corroborated by new U-Pb dating providing new evidence for a complex mass extinction scenario. The massive Deccan eruptions of phase-2 began in the latest Maastrichtian C29r and ended at or near the Cretaceous-Tertiary boundary (KTB) depositing ~3000 m of stacked lava flows or 80% of the total Deccan eruptions over a period of just 250 ky. The onset of phase-2 eruptions coincided with rapid global warming on land (8°C) and oceans (4°C) and increasingly high-stress environments evident by dwarfed species and decreased diversity preceding the mass extinction in planktic foraminiferal zones CF2-CF1. Deep cores in the Krishna-Godavari Basin, SE India, document the rapid mass extinction of planktic foraminifera in intertrappean sediments between four major volcanic eruptions known as the longest lava flows on Earth. Maximum stress is observed globally approaching the end of the Maastrichtian with faunal assemblages dominated (~90%) by the disaster opportunist Guembelitria cretacea. This interval correlates with the massive eruptions of the world's longest lava flows, renewed rapid global warming and ocean acidification during the last ~50 ky of the Maastrichtian. The Chicxulub impact occurred during the global warming near the base of zone CF1 preceding the mass extinction by <100 ky (depending on the time scale used). This age estimate is based on the stratigraphically oldest impact spherule layer in NE Mexico, Texas, and Yucatan crater core Yaxcopoil-1. In all other regions (e.g., North Atlantic, Caribbean, Belize, Guatemala, southern Mexico) impact spherules are reworked in early Danian sediments (zone P1a) at least 100 ky after the KTB due to Gulf Stream erosion and increased tectonic activity in the region. No species extinctions are associated with the Chicxulub impact. Any KTB mass extinction scenario

  13. Community stability and selective extinction during the Permian-Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Roopnarine, Peter D.; Angielczyk, Kenneth D.

    2015-10-01

    The fossil record contains exemplars of extreme biodiversity crises. Here, we examined the stability of terrestrial paleocommunities from South Africa during Earth's most severe mass extinction, the Permian-Triassic. We show that stability depended critically on functional diversity and patterns of guild interaction, regardless of species richness. Paleocommunities exhibited less transient instability—relative to model communities with alternative community organization—and significantly greater probabilities of being locally stable during the mass extinction. Functional patterns that have evolved during an ecosystem's history support significantly more stable communities than hypothetical alternatives.

  14. Has the Earth's sixth mass extinction already arrived?

    PubMed

    Barnosky, Anthony D; Matzke, Nicholas; Tomiya, Susumu; Wogan, Guinevere O U; Swartz, Brian; Quental, Tiago B; Marshall, Charles; McGuire, Jenny L; Lindsey, Emily L; Maguire, Kaitlin C; Mersey, Ben; Ferrer, Elizabeth A

    2011-03-03

    Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540 million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis. Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.

  15. What Caused the Mass Extinction?

    ERIC Educational Resources Information Center

    Alvarez, Walter; And Others

    1990-01-01

    Presented are the arguments of two different points of view on the mass extinction of the dinosaurs. Evidence of extraterrestrial impact theory and massive volcanic eruption theory are discussed. (CW)

  16. Mass extinctions: Ecological selectivity and primary production

    NASA Astrophysics Data System (ADS)

    Rhodes, Melissa Clark; Thayer, Charles W.

    1991-09-01

    If mass extinctions were caused by reduced primary productivity, then extinctions should be concentrated among animals with starvation-susceptible feeding modes, active lifestyles, and high-energy budgets. The stratigraphic ranges (by stage) of 424 genera of bivalves and 309 genera of articulate brachiopods suggest that there was an unusual reduction of primary productivity at the Cretaceous/Tertiary (K/T) boundary extinction. For bivalves at the K/T, there were (1) selective extinction of suspension feeders and other susceptible trophic categories relative to deposit feeders and other resistant categories, and (2) among suspension feed-ers, selective extinction of bivalves with active locomotion. During the Permian-Triassic (P/Tr) extinction and Jurassic background time, extinction rates among suspension feeders were greater for articulate brachiopods than for bivalves. But during the K/T event, extinction rates of articulates and suspension-feeding bivalves equalized, possibly because the low-energy budgets of articulates gave them an advantage when food was scarce.

  17. Accelerated modern human-induced species losses: Entering the sixth mass extinction.

    PubMed

    Ceballos, Gerardo; Ehrlich, Paul R; Barnosky, Anthony D; García, Andrés; Pringle, Robert M; Palmer, Todd M

    2015-06-01

    The oft-repeated claim that Earth's biota is entering a sixth "mass extinction" depends on clearly demonstrating that current extinction rates are far above the "background" rates prevailing between the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing.

  18. End-Triassic mass extinction started by intrusive CAMP activity.

    PubMed

    Davies, J H F L; Marzoli, A; Bertrand, H; Youbi, N; Ernesto, M; Schaltegger, U

    2017-05-31

    The end-Triassic extinction is one of the Phanerozoic's largest mass extinctions. This extinction is typically attributed to climate change associated with degassing of basalt flows from the central Atlantic magmatic province (CAMP). However, recent work suggests that the earliest known CAMP basalts occur above the extinction horizon and that climatic and biotic changes began before the earliest known CAMP eruptions. Here we present new high-precision U-Pb ages from CAMP mafic intrusive units, showing that magmatic activity was occurring ∼100 Kyr ago before the earliest known eruptions. We correlate the early magmatic activity with the onset of changes to the climatic and biotic records. We also report ages from sills in an organic rich sedimentary basin in Brazil that intrude synchronously with the extinction suggesting that degassing of these organics contributed to the climate change which drove the extinction. Our results indicate that the intrusive record from large igneous provinces may be more important for linking to mass extinctions than the eruptive record.

  19. End-Triassic mass extinction started by intrusive CAMP activity

    NASA Astrophysics Data System (ADS)

    Davies, J. H. F. L.; Marzoli, A.; Bertrand, H.; Youbi, N.; Ernesto, M.; Schaltegger, U.

    2017-05-01

    The end-Triassic extinction is one of the Phanerozoic's largest mass extinctions. This extinction is typically attributed to climate change associated with degassing of basalt flows from the central Atlantic magmatic province (CAMP). However, recent work suggests that the earliest known CAMP basalts occur above the extinction horizon and that climatic and biotic changes began before the earliest known CAMP eruptions. Here we present new high-precision U-Pb ages from CAMP mafic intrusive units, showing that magmatic activity was occurring ~100 Kyr ago before the earliest known eruptions. We correlate the early magmatic activity with the onset of changes to the climatic and biotic records. We also report ages from sills in an organic rich sedimentary basin in Brazil that intrude synchronously with the extinction suggesting that degassing of these organics contributed to the climate change which drove the extinction. Our results indicate that the intrusive record from large igneous provinces may be more important for linking to mass extinctions than the eruptive record.

  20. Accelerated modern human–induced species losses: Entering the sixth mass extinction

    PubMed Central

    Ceballos, Gerardo; Ehrlich, Paul R.; Barnosky, Anthony D.; García, Andrés; Pringle, Robert M.; Palmer, Todd M.

    2015-01-01

    The oft-repeated claim that Earth’s biota is entering a sixth “mass extinction” depends on clearly demonstrating that current extinction rates are far above the “background” rates prevailing between the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing. PMID:26601195

  1. Chronology of magmatic and biological events during mass extinctions

    NASA Astrophysics Data System (ADS)

    Schaltegger, U.; Davies, J.; Baresel, B.; Bucher, H.

    2016-12-01

    For mass extinctions, high-precision geochronology is key to understanding: 1) the age and duration of mass extinction intervals, derived from palaeo-biodiversity or chemical proxies in marine sections, and 2) the age and duration of the magmatism responsible for injecting volatiles into the atmosphere. Using high-precision geochronology, here we investigate the sequence of events linked to the Triassic-Jurassic boundary (TJB) and the Permian-Triassic boundary (PTB) mass extinctions. At the TJB, the model of Guex et al. (2016) invokes degassing of early magmas produced by thermal erosion of cratonic lithosphere as a trigger of climate disturbance in the late Rhaetian. We provide geochronological evidence that such early intrusives from the CAMP (Central Atlantic Magmatic Province), predate the end-Triassic extinction event (Blackburn et al. 2013) by 100 kyr (Davies et al., subm.). We propose that these early intrusions and associated explosive volcanism (currently unidentified) initiate the extinction, followed by the younger basalt eruptions of the CAMP. We also provide accurate and precise calibration of the PTB in marine sections in S. China: The PTB and the extinction event coincide within 30 kyr in deep water settings; a hiatus followed by microbial limestone deposition in shallow water settings is of <100 kyr duration. The PTB extinction interval is preceded by up to 300 kyr by the onset of partly alkaline explosive, extrusive and intrusive rocks, which are suggested as the trigger of the mass extinction, rather than the subsequent basalt flows of the Siberian Traps (Burgess and Bowring 2015). From temporal constraints, the main inferences that can be made are: The duration of extinction events is in the x10 kyr range during the initial intrusive activity of a Large Igneous Province, and is postdated by the majority of basalt flows over several 100 kyr. For modeling climate change associated with mass extinctions, volatiles released from the basalt flows may

  2. A sudden end-Permian mass extinction (Invited)

    NASA Astrophysics Data System (ADS)

    Shen, S.

    2013-12-01

    The end-Permian mass extinction is the largest of the Phanerozoic. In the immediate aftermath the marine ecosystem was dominated by microbial and communities with disaster taxa. Plausible kill mechanism includes an extremely rapid, explosive release of gases such as carbon dioxide, methane and hydrogen sulfide. Siberian flood volcanism has been suggested as the most possible mechanism to trigger the massive release of greenhouse gases from volcanic eruptions and interaction of magmas with carbon from thick organic-rich deposits or rapid venting of coal-derived methane or massive combustion of coal. A sharp δ13C isotopic excursion, rapid disappearance of carbonate benthic communities and δ18O data from conodont apatite suggest rapid global warming. The end-Permian mass extinction occurred in less than 200,000 years. This extinction interval is constrained by two ash beds (Beds 25 and 28) at the Meishan section. However, the extinction patterns remain controversial largely due to the condensed nature of the Meishan sections. Geochemical signals and their interpretations are also contentious. Thus, the level of achievable stratigraphic resolution becomes crucial to determine the nature of the event and a detailed study of the extinction interval is essential to unravel the extinction pattern, chemostratigraphy, and the causes. However, the extinction interval at Meishan is only 26 cm thick and contains distinct gaps at the Permian-Triassic boundary (PTB) and possibly the base of Bed 25. Thus, it is impossible to resolve a detailed extinction pattern. Studying expanded sections is crucial to understand the detailed events before, during and after the main extinction. In this report, we show a highly-expanded Permian-Triassic boundary section in Guangxi Province, South China. The last 4.5 m between beds 22 and 28 of the Meishan sections is represented by a sequence of ~560 m at the section and the extinction interval between beds 24e and 28 at Meishan is represented

  3. Periodic Impact Cratering and Extinction Events Over the Last 260 Million Years

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Caldeira, Ken

    2015-01-01

    The claims of periodicity in impact cratering and biological extinction events are controversial. Anewly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8 +/- 0.6 Myr cycle. Using the same method, we found a significant 27.0 +/- 0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 11 apparent peaks in the last 260 Myr, at least 5 of which correlate closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable.

  4. Calibrating the end-Permian mass extinction.

    PubMed

    Shen, Shu-zhong; Crowley, James L; Wang, Yue; Bowring, Samuel A; Erwin, Douglas H; Sadler, Peter M; Cao, Chang-qun; Rothman, Daniel H; Henderson, Charles M; Ramezani, Jahandar; Zhang, Hua; Shen, Yanan; Wang, Xiang-dong; Wang, Wei; Mu, Lin; Li, Wen-zhong; Tang, Yue-gang; Liu, Xiao-lei; Liu, Lu-jun; Zeng, Yong; Jiang, Yao-fa; Jin, Yu-gan

    2011-12-09

    The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ(13)C over 90,000 years, and coincided with a δ(13)C excursion of -5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

  5. Mass extinctions drove increased global faunal cosmopolitanism on the supercontinent Pangaea.

    PubMed

    Button, David J; Lloyd, Graeme T; Ezcurra, Martín D; Butler, Richard J

    2017-10-10

    Mass extinctions have profoundly impacted the evolution of life through not only reducing taxonomic diversity but also reshaping ecosystems and biogeographic patterns. In particular, they are considered to have driven increased biogeographic cosmopolitanism, but quantitative tests of this hypothesis are rare and have not explicitly incorporated information on evolutionary relationships. Here we quantify faunal cosmopolitanism using a phylogenetic network approach for 891 terrestrial vertebrate species spanning the late Permian through Early Jurassic. This key interval witnessed the Permian-Triassic and Triassic-Jurassic mass extinctions, the onset of fragmentation of the supercontinent Pangaea, and the origins of dinosaurs and many modern vertebrate groups. Our results recover significant increases in global faunal cosmopolitanism following both mass extinctions, driven mainly by new, widespread taxa, leading to homogenous 'disaster faunas'. Cosmopolitanism subsequently declines in post-recovery communities. These shared patterns in both biotic crises suggest that mass extinctions have predictable influences on animal distribution and may shed light on biodiversity loss in extant ecosystems.Mass extinctions are thought to produce 'disaster faunas', communities dominated by a small number of widespread species. Here, Button et al. develop a phylogenetic network approach to test this hypothesis and find that mass extinctions did increase faunal cosmopolitanism across Pangaea during the late Palaeozoic and early Mesozoic.

  6. Ecological selectivity of the emerging mass extinction in the oceans.

    PubMed

    Payne, Jonathan L; Bush, Andrew M; Heim, Noel A; Knope, Matthew L; McCauley, Douglas J

    2016-09-16

    To better predict the ecological and evolutionary effects of the emerging biodiversity crisis in the modern oceans, we compared the association between extinction threat and ecological traits in modern marine animals to associations observed during past extinction events using a database of 2497 marine vertebrate and mollusc genera. We find that extinction threat in the modern oceans is strongly associated with large body size, whereas past extinction events were either nonselective or preferentially removed smaller-bodied taxa. Pelagic animals were victimized more than benthic animals during previous mass extinctions but are not preferentially threatened in the modern ocean. The differential importance of large-bodied animals to ecosystem function portends greater future ecological disruption than that caused by similar levels of taxonomic loss in past mass extinction events. Copyright © 2016, American Association for the Advancement of Science.

  7. Effect of climate-related mass extinctions on escalation in molluscs

    NASA Astrophysics Data System (ADS)

    Hansen, Thor A.; Kelley, Patricia H.; Melland, Vicky D.; Graham, Scott E.

    1999-12-01

    We test the hypothesis that escalated species (e.g., those with antipredatory adaptations such as heavy armor) are more vulnerable to extinctions caused by changes in climate. If this hypothesis is valid, recovery faunas after climate-related extinctions should include significantly fewer species with escalated shell characteristics, and escalated species should undergo greater rates of extinction than nonescalated species. This hypothesis is tested for the Cretaceous-Paleocene, Eocene-Oligocene, middle Miocene, and Pliocene-Pleistocene mass extinctions. Gastropod and bivalve molluscs from the U.S. coastal plain were evaluated for 10 shell characters that confer resistance to predators. Of 40 tests, one supported the hypothesis; highly ornamented gastropods underwent greater levels of Pliocene-Pleistocene extinction than did nonescalated species. All remaining tests were nonsignificant. The hypothesis that escalated species are more vulnerable to climate-related mass extinctions is not supported.

  8. Rarity in mass extinctions and the future of ecosystems

    NASA Astrophysics Data System (ADS)

    Hull, Pincelli M.; Darroch, Simon A. F.; Erwin, Douglas H.

    2015-12-01

    The fossil record provides striking case studies of biodiversity loss and global ecosystem upheaval. Because of this, many studies have sought to assess the magnitude of the current biodiversity crisis relative to past crises—a task greatly complicated by the need to extrapolate extinction rates. Here we challenge this approach by showing that the rarity of previously abundant taxa may be more important than extinction in the cascade of events leading to global changes in the biosphere. Mass rarity may provide the most robust measure of our current biodiversity crisis relative to those past, and new insights into the dynamics of mass extinction.

  9. Biogeographic and bathymetric determinants of brachiopod extinction and survival during the Late Ordovician mass extinction.

    PubMed

    Finnegan, Seth; Rasmussen, Christian M Ø; Harper, David A T

    2016-04-27

    The Late Ordovician mass extinction (LOME) coincided with dramatic climate changes, but there are numerous ways in which these changes could have driven marine extinctions. We use a palaeobiogeographic database of rhynchonelliform brachiopods to examine the selectivity of Late Ordovician-Early Silurian genus extinctions and evaluate which extinction drivers are best supported by the data. The first (latest Katian) pulse of the LOME preferentially affected genera restricted to deeper waters or to relatively narrow (less than 35°) palaeolatitudinal ranges. This pattern is only observed in the latest Katian, suggesting that it reflects drivers unique to this interval. Extinction of exclusively deeper-water genera implies that changes in water mass properties such as dissolved oxygen content played an important role. Extinction of genera with narrow latitudinal ranges suggests that interactions between shifting climate zones and palaeobiogeography may also have been important. We test the latter hypothesis by estimating whether each genus would have been able to track habitats within its thermal tolerance range during the greenhouse-icehouse climate transition. Models including these estimates are favoured over alternative models. We argue that the LOME, long regarded as non-selective, is highly selective along biogeographic and bathymetric axes that are not closely correlated with taxonomic identity. © 2016 The Author(s).

  10. Biogeographic and bathymetric determinants of brachiopod extinction and survival during the Late Ordovician mass extinction

    PubMed Central

    Finnegan, Seth; Rasmussen, Christian M. Ø.; Harper, David A. T.

    2016-01-01

    The Late Ordovician mass extinction (LOME) coincided with dramatic climate changes, but there are numerous ways in which these changes could have driven marine extinctions. We use a palaeobiogeographic database of rhynchonelliform brachiopods to examine the selectivity of Late Ordovician–Early Silurian genus extinctions and evaluate which extinction drivers are best supported by the data. The first (latest Katian) pulse of the LOME preferentially affected genera restricted to deeper waters or to relatively narrow (less than 35°) palaeolatitudinal ranges. This pattern is only observed in the latest Katian, suggesting that it reflects drivers unique to this interval. Extinction of exclusively deeper-water genera implies that changes in water mass properties such as dissolved oxygen content played an important role. Extinction of genera with narrow latitudinal ranges suggests that interactions between shifting climate zones and palaeobiogeography may also have been important. We test the latter hypothesis by estimating whether each genus would have been able to track habitats within its thermal tolerance range during the greenhouse–icehouse climate transition. Models including these estimates are favoured over alternative models. We argue that the LOME, long regarded as non-selective, is highly selective along biogeographic and bathymetric axes that are not closely correlated with taxonomic identity. PMID:27122567

  11. Surviving Mass Extinctions through Biomineralized DNA.

    PubMed

    Turon, Pau; Puiggalí, Jordi; Bertrán, Oscar; Alemán, Carlos

    2015-12-21

    Even in the worst of conditions, such as those which occurred during mass extinction events, life on Earth never totally stopped. Aggressive chemical and physical attacks able to sterilize or poison living organisms occurred repeatedly. Surprisingly, DNA was not degraded, denatured or modified to the point of losing the capability of transferring the genetic information to the next generations. After the events of mass extinction life was able to survive and thrive. DNA was passed on despite being an extremely fragile biomolecule. The potential implications of hydroxyapatite protection of DNA are discussed in this Concept article including how DNA acts as a template for hydroxyapatite (HAp) formation, how cell death can trigger biomineralization, and how DNA can be successfully released from HAp when the conditions are favorable for life. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Estimates of the magnitudes of major marine mass extinctions in earth history

    PubMed Central

    2016-01-01

    Procedures introduced here make it possible, first, to show that background (piecemeal) extinction is recorded throughout geologic stages and substages (not all extinction has occurred suddenly at the ends of such intervals); second, to separate out background extinction from mass extinction for a major crisis in earth history; and third, to correct for clustering of extinctions when using the rarefaction method to estimate the percentage of species lost in a mass extinction. Also presented here is a method for estimating the magnitude of the Signor–Lipps effect, which is the incorrect assignment of extinctions that occurred during a crisis to an interval preceding the crisis because of the incompleteness of the fossil record. Estimates for the magnitudes of mass extinctions presented here are in most cases lower than those previously published. They indicate that only ∼81% of marine species died out in the great terminal Permian crisis, whereas levels of 90–96% have frequently been quoted in the literature. Calculations of the latter numbers were incorrectly based on combined data for the Middle and Late Permian mass extinctions. About 90 orders and more than 220 families of marine animals survived the terminal Permian crisis, and they embodied an enormous amount of morphological, physiological, and ecological diversity. Life did not nearly disappear at the end of the Permian, as has often been claimed. PMID:27698119

  13. Estimates of the magnitudes of major marine mass extinctions in earth history

    NASA Astrophysics Data System (ADS)

    Stanley, Steven M.

    2016-10-01

    Procedures introduced here make it possible, first, to show that background (piecemeal) extinction is recorded throughout geologic stages and substages (not all extinction has occurred suddenly at the ends of such intervals); second, to separate out background extinction from mass extinction for a major crisis in earth history; and third, to correct for clustering of extinctions when using the rarefaction method to estimate the percentage of species lost in a mass extinction. Also presented here is a method for estimating the magnitude of the Signor-Lipps effect, which is the incorrect assignment of extinctions that occurred during a crisis to an interval preceding the crisis because of the incompleteness of the fossil record. Estimates for the magnitudes of mass extinctions presented here are in most cases lower than those previously published. They indicate that only ˜81% of marine species died out in the great terminal Permian crisis, whereas levels of 90-96% have frequently been quoted in the literature. Calculations of the latter numbers were incorrectly based on combined data for the Middle and Late Permian mass extinctions. About 90 orders and more than 220 families of marine animals survived the terminal Permian crisis, and they embodied an enormous amount of morphological, physiological, and ecological diversity. Life did not nearly disappear at the end of the Permian, as has often been claimed.

  14. Estimates of the magnitudes of major marine mass extinctions in earth history.

    PubMed

    Stanley, Steven M

    2016-10-18

    Procedures introduced here make it possible, first, to show that background (piecemeal) extinction is recorded throughout geologic stages and substages (not all extinction has occurred suddenly at the ends of such intervals); second, to separate out background extinction from mass extinction for a major crisis in earth history; and third, to correct for clustering of extinctions when using the rarefaction method to estimate the percentage of species lost in a mass extinction. Also presented here is a method for estimating the magnitude of the Signor-Lipps effect, which is the incorrect assignment of extinctions that occurred during a crisis to an interval preceding the crisis because of the incompleteness of the fossil record. Estimates for the magnitudes of mass extinctions presented here are in most cases lower than those previously published. They indicate that only ∼81% of marine species died out in the great terminal Permian crisis, whereas levels of 90-96% have frequently been quoted in the literature. Calculations of the latter numbers were incorrectly based on combined data for the Middle and Late Permian mass extinctions. About 90 orders and more than 220 families of marine animals survived the terminal Permian crisis, and they embodied an enormous amount of morphological, physiological, and ecological diversity. Life did not nearly disappear at the end of the Permian, as has often been claimed.

  15. Can we avoid the Sixth Mass Extinction? Setting today's extinction crisis in the context of the Big Five

    NASA Astrophysics Data System (ADS)

    Barnosky, A. D.

    2012-12-01

    While the ultimate extinction driver now—Homo sapiens—is unique with respect to the drivers of past extinctions, comparison of parallel neontological and paleontological information helps calibrate how far the so-called Sixth Mass Extinction has progressed and whether it is inevitable. Such comparisons document that rates of extinction today are approaching or exceeding those that characterized the Big Five Mass Extinctions. Continuation of present extinction rates for vertebrates, for example, would result in 75% species loss—the minimum benchmark exhibited in the Big Five extinctions—within 3 to 22 centuries, assuming constant rates of loss and no threshold effects. Preceding and during each of the Big Five, the global ecosystem experienced major changes in climate, atmospheric chemisty, and ocean chemistry—not unlike what is being observed presently. Nevertheless, only 1-2% of well-assessed modern species have been lost over the past five centuries, still far below what characterized past mass extinctions in the strict paleontological sense. For mammals, adding in the end-Pleistocene species that died out would increase the species-loss percentage by some 5%. If threatened vertebrate species were to actually go extinct, losses would rise to between 14 and 40%, depending on the group. Such observations highlight that, although many species have already had their populations drastically reduced to near-critical levels, the Sixth Mass Extinction has not yet progressed to the point where it is unavoidable. Put another way, the vast majority of species that have occupied the world in concert with Homo sapiens are still alive and are possible to save. That task, however, will require slowing the abnormally high extinction rates that are now in progress, which in turn requires unified efforts to cap human population growth, decrease the average human footprint, reduce fossil fuel use while simultaneously increasing clean energy technologies, integrate

  16. Major Optical Depth Perturbations to the Stratosphere from Volcanic Eruptions: Stellar-Extinction Period, 1961-1978

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.; Hansen, James E. (Technical Monitor)

    2001-01-01

    A revised chronology of stratospheric aerosol extinction due to volcanic eruptions has been assembled for the period 1961-1978, which immediately precedes the era of dedicated satellite measurements. On the whole, the most accurate data consist of published observations of stellar extinction, supplemented in part by other kinds of observational data. The period covered encompasses the important eruptions of Agung (1963) and Fuego (1974), whose dust veils are discussed with respect to their transport, decay, and total mass. The effective (area-weighted mean) radii of the aerosols for both eruptions are found to be 0.3-0.4 microns. It is confirmed that, among known tropical eruptions, Agung's dust was unique for a low-latitude eruption in remaining almost entirely confined to the hemisphere of its production. A new table of homogeneous visual optical depth perturbations, listed by year and by hemisphere, is provided for the whole period 1881-1978, including the pyrheliometric period before 1961 that was investigated previously.

  17. Calcium isotope constraints on the end-Permian mass extinction

    PubMed Central

    Payne, Jonathan L.; Turchyn, Alexandra V.; Paytan, Adina; DePaolo, Donald J.; Lehrmann, Daniel J.; Yu, Meiyi; Wei, Jiayong

    2010-01-01

    The end-Permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope (δ13C) composition of carbonate minerals. Several extinction scenarios consistent with these observations have been put forward. Secular variation in the calcium isotope (δ44/40Ca) composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction. Here we report δ44/40Ca across the Permian-Triassic boundary from marine limestone in south China. The δ44/40Ca exhibits a transient negative excursion of ∼0.3‰ over a few hundred thousand years or less, which we interpret to reflect a change in the global δ44/40Ca composition of seawater. CO2-driven ocean acidification best explains the coincidence of the δ44/40Ca excursion with negative excursions in the δ13C of carbonates and organic matter and the preferential extinction of heavily calcified marine animals. Calcium isotope constraints on carbon cycle calculations suggest that the average δ13C of CO2 released was heavier than -28‰ and more likely near -15‰; these values indicate a source containing substantial amounts of mantle- or carbonate-derived carbon. Collectively, the results point toward Siberian Trap volcanism as the trigger of mass extinction. PMID:20421502

  18. Intra-accumbal Cannabinoid Agonist Attenuated Reinstatement but not Extinction Period of Morphine-Induced Conditioned Place Preference; Evidence for Different Characteristics of Extinction Period and Reinstatement.

    PubMed

    Khaleghzadeh-Ahangar, Hossein; Haghparast, Abbas

    2017-11-01

    The brain reward system consists of the ventral tegmental area that sends its dopaminergic projections to the forebrain, cortical areas, amygdala and largely to the nucleus accumbens (NAc). The present study aims were to investigate the effects of bilateral intra-accumbal microinjection of WIN55,212-2, a CB1 receptor agonist, on the duration of extinction period and reinstatement to morphine by the conditioned place preference (CPP) paradigm in the rat. Forty-six adult male albino Wistar rats received intra-accumbal WIN55,212-2 [p0.5, 1 and 2 mM/0.5 μl dimethyl sulfoxide (DMSO)] injections bilaterally. To induce CPP, morphine (5 mg/kg) was injected subcutaneously over three consecutive days. The results showed that intra-NAc administration of WIN55,212-2 during the extinction period had no effect on its duration but single administration of the1 mM/0.5 μl DMSO dose just before the reinstatement phase significantly attenuated its conditioning score. This is the first time that interactions of opioid and cannabinoid systems by local activation of CB1 receptors in the NAc during extinction and morphine-induced reinstatement were investigated. The CB1 agonist can inhibit and eliminate the reward-associated memory of morphine and the conditioning score in reinstatement but not in the extinction period. Our findings suggest that the extinction period and reinstatement could occur through different mechanisms.

  19. Eutrophication, microbial-sulfate reduction and mass extinctions

    PubMed Central

    Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

    2016-01-01

    ABSTRACT In post-Cambrian time, life on Earth experienced 5 major extinction events, likely instigated by adverse environmental conditions. Biodiversity loss among marine taxa, for at least 3 of these mass extinction events (Late Devonian, end-Permian and end-Triassic), has been connected with widespread oxygen-depleted and sulfide-bearing marine water. Furthermore, geochemical and sedimentary evidence suggest that these events correlate with rather abrupt climate warming and possibly increased terrestrial weathering. This suggests that biodiversity loss may be triggered by mechanisms intrinsic to the Earth system, notably, the biogeochemical sulfur and carbon cycle. This climate warming feedback produces large-scale eutrophication on the continental shelf, which, in turn, expands oxygen minimum zones by increased respiration, which can turn to a sulfidic state by increased microbial-sulfate reduction due to increased availability of organic matter. A plankton community turnover from a high-diversity eukaryote to high-biomass bacterial dominated food web is the catalyst proposed in this anoxia-extinction scenario and stands in stark contrast to the postulated productivity collapse suggested for the end-Cretaceous mass extinction. This cascade of events is relevant for the future ocean under predicted greenhouse driven climate change. The exacerbation of anoxic “dead” zones is already progressing in modern oceanic environments, and this is likely to increase due to climate induced continental weathering and resulting eutrophication of the oceans. PMID:27066181

  20. Mass Extinctions of Pangea (Jean Baptiste Lamarck Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Wignall, Paul B.

    2017-04-01

    The 80 million years of Earth history from middle of the Permian to the early Jurassic were some of the worst life ever experienced. The interval includes two mass extinctions that bracket the Triassic period and several lesser crises. It was to be nearly another 120 million years before another major crisis was to strike (this time it was the famous one that removed the dinosaurs). So what was so bad about the 80 million years and why was it so good afterwards? My talk will try to provide at least some of the answers. There are plenty of clues. Notably, the interval coincides with the presence of the Pangea supercontinent and all the extinctions coincided with the eruption of large igneous provinces (LIPs). Indeed, every LIP of this interval coincides with an extinction crisis, a perfect correlation that completely breaks down afterwards. However, getting from correlation to causation is far from straight forward. There are many unknowns - how much gas was released by the volcanism, how quickly and what type of gases were they? These are all questions under investigation. Most of the extinctions of Pangean time coincide with rapid global warming and extensive marine anoxia suggesting that greenhouse gas emissions linked to volcanism were an important extinction driver. For the most severe crises (Permo-Triassic and end-Triassic) losses occurred throughout the food chain all the way down to the primary producers of the oceans and across all habitats including terrestrial ecosystems. At the other end of the spectrum of disaster, the lesser extinctions (Toarcian, Smithian/Spathian) only affected marine invertebrates. The full panoply of catastrophe was played out during the Permo-Triassic mass extinction and has received the most attention. The record in South China shows that there were two phases of extinction. These straddle the boundary and show selective losses initially for shallow-water organisms that were susceptible to high temperatures and then for deeper

  1. THE OBSERVED RELATION BETWEEN STELLAR MASS, DUST EXTINCTION, AND STAR FORMATION RATE IN LOCAL GALAXIES

    SciTech Connect

    Zahid, H. J.; Kewley, L. J.; Kudritzki, R. P.

    In this study, we investigate the relation between stellar mass, dust extinction, and star formation rate (SFR) using {approx}150,000 star-forming galaxies from SDSS DR7. We show that the relation between dust extinction and SFR changes with stellar mass. For galaxies at the same stellar mass, dust extinction is anti-correlated with the SFR at stellar masses <10{sup 10} M {sub Sun }. There is a sharp transition in the relation at a stellar mass of 10{sup 10} M {sub Sun }. At larger stellar masses, dust extinction is positively correlated with the SFR for galaxies at the same stellar mass. Themore » observed relation between stellar mass, dust extinction, and SFR presented in this study helps to confirm similar trends observed in the relation between stellar mass, metallicity, and SFR. The relation reported in this study provides important new constraints on the physical processes governing the chemical evolution of galaxies. The correlation between SFR and dust extinction for galaxies with stellar masses >10{sup 10} M {sub Sun} is shown to extend to the population of quiescent galaxies suggesting that the physical processes responsible for the observed relation between stellar mass, dust extinction, and SFR may be related to the processes leading to the shutdown of star formation in galaxies.« less

  2. Biological extinction in earth history

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1986-01-01

    Virtually all plant and animal species that have ever lived on the earth are extinct. For this reason alone, extinction must play an important role in the evolution of life. The five largest mass extinctions of the past 600 million years are of greatest interest, but there is also a spectrum of smaller events, many of which indicate biological systems in profound stress. Extinction may be episodic at all scales, with relatively long periods of stability alternating with short-lived extinction events. Most extinction episodes are biologically selective, and further analysis of the victims and survivors offers the greatest chance of deducing the proximal causes of extinction. A drop in sea level and climatic change are most frequently invoked to explain mass extinctions, but new theories of collisions with extraterrestrial bodies are gaining favor. Extinction may be constructive in a Darwinian sense or it may only perturb the system by eliminating those organisms that happen to be susceptible to geologically rare stresses.

  3. Biological Extinction in Earth History

    NASA Astrophysics Data System (ADS)

    Raup, David M.

    1986-03-01

    Virtually all plant and animal species that have ever lived on the earth are extinct. For this reason alone, extinction must play an important role in the evolution of life. The five largest mass extinctions of the past 600 million years are of greatest interest, but there is also a spectrum of smaller events, many of which indicate biological systems in profound stress. Extinction may be episodic at all scales, with relatively long periods of stability alternating with short-lived extinction events. Most extinction episodes are biologically selective, and further analysis of the victims and survivors offers the greatest chance of deducing the proximal causes of extinction. A drop in sea level and climatic change are most frequently invoked to explain mass extinctions, but new theories of collisions with extraterrestrial bodies are gaining favor. Extinction may be constructive in a Darwinian sense or it may only perturb the system by eliminating those organisms that happen to be susceptible to geologically rare stresses.

  4. Breeding Young as a Survival Strategy during Earth's Greatest Mass Extinction.

    PubMed

    Botha-Brink, Jennifer; Codron, Daryl; Huttenlocker, Adam K; Angielczyk, Kenneth D; Ruta, Marcello

    2016-04-05

    Studies of the effects of mass extinctions on ancient ecosystems have focused on changes in taxic diversity, morphological disparity, abundance, behaviour and resource availability as key determinants of group survival. Crucially, the contribution of life history traits to survival during terrestrial mass extinctions has not been investigated, despite the critical role of such traits for population viability. We use bone microstructure and body size data to investigate the palaeoecological implications of changes in life history strategies in the therapsid forerunners of mammals before and after the Permo-Triassic Mass Extinction (PTME), the most catastrophic crisis in Phanerozoic history. Our results are consistent with truncated development, shortened life expectancies, elevated mortality rates and higher extinction risks amongst post-extinction species. Various simulations of ecological dynamics indicate that an earlier onset of reproduction leading to shortened generation times could explain the persistence of therapsids in the unpredictable, resource-limited Early Triassic environments, and help explain observed body size distributions of some disaster taxa (e.g., Lystrosaurus). Our study accounts for differential survival in mammal ancestors after the PTME and provides a methodological framework for quantifying survival strategies in other vertebrates during major biotic crises.

  5. Graptolite community responses to global climate change and the Late Ordovician mass extinction.

    PubMed

    Sheets, H David; Mitchell, Charles E; Melchin, Michael J; Loxton, Jason; Štorch, Petr; Carlucci, Kristi L; Hawkins, Andrew D

    2016-07-26

    Mass extinctions disrupt ecological communities. Although climate changes produce stress in ecological communities, few paleobiological studies have systematically addressed the impact of global climate changes on the fine details of community structure with a view to understanding how changes in community structure presage, or even cause, biodiversity decline during mass extinctions. Based on a novel Bayesian approach to biotope assessment, we present a study of changes in species abundance distribution patterns of macroplanktonic graptolite faunas (∼447-444 Ma) leading into the Late Ordovician mass extinction. Communities at two contrasting sites exhibit significant decreases in complexity and evenness as a consequence of the preferential decline in abundance of dysaerobic zone specialist species. The observed changes in community complexity and evenness commenced well before the dramatic population depletions that mark the tipping point of the extinction event. Initially, community changes tracked changes in the oceanic water masses, but these relations broke down during the onset of mass extinction. Environmental isotope and biomarker data suggest that sea surface temperature and nutrient cycling in the paleotropical oceans changed sharply during the latest Katian time, with consequent changes in the extent of the oxygen minimum zone and phytoplankton community composition. Although many impacted species persisted in ephemeral populations, increased extinction risk selectively depleted the diversity of paleotropical graptolite species during the latest Katian and early Hirnantian. The effects of long-term climate change on habitats can thus degrade populations in ways that cascade through communities, with effects that culminate in mass extinction.

  6. Graptolite community responses to global climate change and the Late Ordovician mass extinction

    NASA Astrophysics Data System (ADS)

    Sheets, H. David; Mitchell, Charles E.; Melchin, Michael J.; Loxton, Jason; Štorch, Petr; Carlucci, Kristi L.; Hawkins, Andrew D.

    2016-07-01

    Mass extinctions disrupt ecological communities. Although climate changes produce stress in ecological communities, few paleobiological studies have systematically addressed the impact of global climate changes on the fine details of community structure with a view to understanding how changes in community structure presage, or even cause, biodiversity decline during mass extinctions. Based on a novel Bayesian approach to biotope assessment, we present a study of changes in species abundance distribution patterns of macroplanktonic graptolite faunas (˜447-444 Ma) leading into the Late Ordovician mass extinction. Communities at two contrasting sites exhibit significant decreases in complexity and evenness as a consequence of the preferential decline in abundance of dysaerobic zone specialist species. The observed changes in community complexity and evenness commenced well before the dramatic population depletions that mark the tipping point of the extinction event. Initially, community changes tracked changes in the oceanic water masses, but these relations broke down during the onset of mass extinction. Environmental isotope and biomarker data suggest that sea surface temperature and nutrient cycling in the paleotropical oceans changed sharply during the latest Katian time, with consequent changes in the extent of the oxygen minimum zone and phytoplankton community composition. Although many impacted species persisted in ephemeral populations, increased extinction risk selectively depleted the diversity of paleotropical graptolite species during the latest Katian and early Hirnantian. The effects of long-term climate change on habitats can thus degrade populations in ways that cascade through communities, with effects that culminate in mass extinction.

  7. Seeking a paleontological signature for mass extinctions caused by flood basalt eruptions

    NASA Astrophysics Data System (ADS)

    Payne, J.; Bush, A. M.; Chang, E. T.; Heim, N. A.; Knope, M. L.; Pruss, S. B.

    2016-12-01

    Flood basalt eruptions coincide with numerous extinction events in the fossil record. Increasingly precise absolute age determinations for both the timing of eruption and of species extinctions have strengthened the case for flood basalt eruptions as the single most important trigger for major mass extinction events in the fossil record. However, the extent to which flood basalt eruptions cause a pattern of biotic loss distinctive from extinctions triggered by other geological or biological processes remains an open question. In the absence of diagnostic mapping between geological triggers and biological losses, establishing the identities of causal agents for mass extinctions will continue to depend primarily on evidence for temporal coincidence. Here we use a synoptic database of marine animal genera spanning the Phanerozoic, including times of first and last occurrence, body size, motility, life position, feeding mode, and respiratory physiology to assess whether extinction events temporally associated with flood basalt eruptions exhibit a diagnostic pattern of extinction selectivity. We further ask whether any events not associated with known large igneous provinces nevertheless display extinction patterns suggestive of such a cause. Finally, we ask whether extinction events associated with other primary causes, such as glaciation or bolide impact, are distinguishable from events apparently triggered by flood basalt eruptions on the basis of extinction selectivity patterns

  8. Catastrophic Events and Mass Extinctions: Impacts and Beyond

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This volume contains extended abstracts that have been accepted for presentation at the conference on Catastrophic Events and Mass Extinctions: Impacts and Beyond, July 9-12, 2000, in Vienna, Austria.

  9. Late Frasnian mass extinction: Conodont event stratigraphy, global changes, and possible causes

    NASA Technical Reports Server (NTRS)

    Sandberg, Charles A.; Ziegler, Willi; Dreesen, Roland; Butler, Jamie L.

    1988-01-01

    Several abrupt changes in conodont biofacies are documented to occur synchronously at six primary control sections across the Frasnian-Famennian boundary in Euramerica. These changes occurred within a time-span of only about 100,000 years near the end of the latest Frasnian linguiformis Zone, which is formally named to replace the Uppermost gigas Zone. The conodont-biofacies changes are interpreted to reflect a eustatic rise followed by an abrupt eustatic fall immediately preceding the late Frasnian mass extinction. Two new conodont species are named and described. Ancyrognathus ubiquitus n.sp. is recorded only just below and above the level of late Frasnian extinction and hence is a global marker for that event. Palmatolepispraetriangularis n.sp. is the long-sought Frasnian ancestor of the formerly cryptogenic species, Pa. triangularis, indicator of the earliest Famennian Lower triangularis Zone. The actual extinction event occurred entirely within the Frasnian and is interpreted to have been of brief duration-from as long as 20,000 years to as short as several days. The eustatic rise-and-fall couplet associated with the late Frasnian mass extinction is similar to eustatic couplets associated with the demise of most Frasnian (F2h) reefs worldwide about 1 m.y. earlier and with a latest Famennian mass extinction about 9.5 m.y. later. All these events may be directly or indirectly attributable to extraterrestrial triggering mechanisms. An impact of a small bolide or a near miss of a larger bolide may have caused the earlier demise of Frasnian reefs. An impact of possibly the same larger bolide in the Southern Hemisphere would explain the late Frasnian mass extinction. Global regression during the Famennian probably resulted from Southern-Hemisphere glaciation triggered by the latest Frasnian impact. Glaciation probably was the indirect cause of the latest Famennian mass extinction.

  10. Periodicity in extinction and the problem of catastrophism in the history of life

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

    1989-01-01

    The hypothesis that extinction events have recurred periodically over the last quarter billion years is greatly strengthened by new data on the stratigraphic ranges of marine animal genera. In the interval from the Permian to Recent, these data encompass some 13,000 generic extinctions, providing a more sensitive indicator of species-level extinctions than previously used familial data. Extinction time series computed from the generic data display nine strong peaks that are nearly uniformly spaced at 26 Ma intervals over the last 270 Ma. Most of these peaks correspond to extinction events recognized in more detailed, if limited, biostratigraphic studies. These new data weaken or negate most arguments against periodicity, which have involved criticisms of the taxonomic data base, sampling intervals, chronometric time scales, and statistical methods used in previous analyses. The criticisms are reviewed in some detail and various new calculations and simulations, including one assessing the effects of paraphyletic taxa, are presented. Although the new data strengthen the case for periodicity, they offer little new insight into the deriving mechanism behind the pattern. However, they do suggest that many of the periodic events may not have been catastrophic, occurring instead over several stratigraphic stages or substages.

  11. Climate change and the selective signature of the Late Ordovician mass extinction.

    PubMed

    Finnegan, Seth; Heim, Noel A; Peters, Shanan E; Fischer, Woodward W

    2012-05-01

    Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia.

  12. Dental Disparity and Ecological Stability in Bird-like Dinosaurs prior to the End-Cretaceous Mass Extinction.

    PubMed

    Larson, Derek W; Brown, Caleb M; Evans, David C

    2016-05-23

    The causes, rate, and selectivity of the end-Cretaceous mass extinction continue to be highly debated [1-5]. Extinction patterns in small, feathered maniraptoran dinosaurs (including birds) are important for understanding extant biodiversity and present an enigma considering the survival of crown group birds (Neornithes) and the extinction of their close kin across the end-Cretaceous boundary [6]. Because of the patchy Cretaceous fossil record of small maniraptorans [7-12], this important transition has not been closely examined in this group. Here, we test the hypothesis that morphological disparity in bird-like dinosaurs was decreasing leading up to the end-Cretaceous mass extinction, as has been hypothesized in some dinosaurs [13, 14]. To test this, we examined tooth morphology, an ecological indicator in fossil reptiles [15-19], from over 3,100 maniraptoran teeth from four groups (Troodontidae, Dromaeosauridae, Richardoestesia, and cf. Aves) across the last 18 million years of the Cretaceous. We demonstrate that tooth disparity, a proxy for variation in feeding ecology, shows no significant decline leading up to the extinction event within any of the groups. Tooth morphospace occupation also remains static over this time interval except for increased size during the early Maastrichtian. Our data provide strong support that extinction within this group occurred suddenly after a prolonged period of ecological stability. To explain this sudden extinction of toothed maniraptorans and the survival of Neornithes, we propose that diet may have been an extinction filter and suggest that granivory associated with an edentulous beak was a key ecological trait in the survival of some lineages. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. Mass extinctions: Persistent problems and new directions

    NASA Technical Reports Server (NTRS)

    Jablonski, D.

    1994-01-01

    Few contest that mass extinctions have punctuated the history of life, or that those events were so pervasive environmentally, taxonomically, and geographically that physical forcing factors were probably involved. However, consensus remains elusive on the nature of those factors, and on how a given perturbation - impact, volcanism, sea-level change, or ocean anoxic event - could actually generate the observed intensity and selectivity of biotic losses. At least two basic problems underlie these long-standing disagreements: difficulties in resolving the fine details of taxon ranges and abundances immediately prior to and after an extinction boundary and the scarcity of simple, unitary cause-and-effect relations in complex biological systems.

  14. Stress-enhanced fear learning in rats is resistant to the effects of immediate massed extinction

    PubMed Central

    Long, Virginia A.; Fanselow, Michael S.

    2014-01-01

    Enhanced fear learning occurs subsequent to traumatic or stressful events and is a persistent challenge to the treatment of post-traumatic stress disorder (PTSD). Facilitation of learning produced by prior stress can elicit an exaggerated fear response to a minimally aversive event or stimulus. Stress-enhanced fear learning (SEFL) is a rat model of PTSD; rats previously exposed to the SEFL 15 electrical shocks procedure exhibit several behavioral responses similar to those seen in patients with PTSD. However, past reports found that SEFL is not mitigated by extinction (a model of exposure therapy) when the spaced extinction began 24 h after stress. Recent studies found that extinction from 10 min to 1 h subsequent to fear conditioning “erased” learning, whereas later extinction, occurring from 24 to 72 h after conditioning did not. Other studies indicate that massed extinction is more effective than spaced procedures. Therefore, we examined the time-dependent nature of extinction on the stress-induced enhancement of fear learning using a massed trial’s procedure. Experimental rats received 15 foot shocks and were given either no extinction or massed extinction 10 min or 72 h later. Our present data indicate that SEFL, following traumatic stress, is resistant to immediate massed extinction. Experimental rats showed exaggerated new fear learning regardless of when extinction training occurred. Thus, post-traumatic reactivity such as SEFL does not seem responsive to extinction treatments. PMID:22176467

  15. Breeding Young as a Survival Strategy during Earth’s Greatest Mass Extinction

    NASA Astrophysics Data System (ADS)

    Botha-Brink, Jennifer; Codron, Daryl; Huttenlocker, Adam K.; Angielczyk, Kenneth D.; Ruta, Marcello

    2016-04-01

    Studies of the effects of mass extinctions on ancient ecosystems have focused on changes in taxic diversity, morphological disparity, abundance, behaviour and resource availability as key determinants of group survival. Crucially, the contribution of life history traits to survival during terrestrial mass extinctions has not been investigated, despite the critical role of such traits for population viability. We use bone microstructure and body size data to investigate the palaeoecological implications of changes in life history strategies in the therapsid forerunners of mammals before and after the Permo-Triassic Mass Extinction (PTME), the most catastrophic crisis in Phanerozoic history. Our results are consistent with truncated development, shortened life expectancies, elevated mortality rates and higher extinction risks amongst post-extinction species. Various simulations of ecological dynamics indicate that an earlier onset of reproduction leading to shortened generation times could explain the persistence of therapsids in the unpredictable, resource-limited Early Triassic environments, and help explain observed body size distributions of some disaster taxa (e.g., Lystrosaurus). Our study accounts for differential survival in mammal ancestors after the PTME and provides a methodological framework for quantifying survival strategies in other vertebrates during major biotic crises.

  16. Species extinction thresholds in the face of spatially correlated periodic disturbance.

    PubMed

    Liao, Jinbao; Ying, Zhixia; Hiebeler, David E; Wang, Yeqiao; Takada, Takenori; Nijs, Ivan

    2015-10-20

    The spatial correlation of disturbance is gaining attention in landscape ecology, but knowledge is still lacking on how species traits determine extinction thresholds under spatially correlated disturbance regimes. Here we develop a pair approximation model to explore species extinction risk in a lattice-structured landscape subject to aggregated periodic disturbance. Increasing disturbance extent and frequency accelerated population extinction irrespective of whether dispersal was local or global. Spatial correlation of disturbance likewise increased species extinction risk, but only for local dispersers. This indicates that models based on randomly simulated disturbances (e.g., mean-field or non-spatial models) may underestimate real extinction rates. Compared to local dispersal, species with global dispersal tolerated more severe disturbance, suggesting that the spatial correlation of disturbance favors long-range dispersal from an evolutionary perspective. Following disturbance, intraspecific competition greatly enhanced the extinction risk of distance-limited dispersers, while it surprisingly did not influence the extinction thresholds of global dispersers, apart from decreasing population density to some degree. As species respond differently to disturbance regimes with different spatiotemporal properties, different regimes may accommodate different species.

  17. Widespread habitat change through paludification as an interactive mechanism in mass extinction events

    NASA Technical Reports Server (NTRS)

    Klinger, L. F.

    1988-01-01

    The study of mass extinction events has largely focused on defining an environmental factor or factors that might account for specific patterns of faunal demise. Several hypotheses elaborate on how a given environmental factor might affect fauna directly, but differentially, causing extinction in certain taxa but not others. Yet few studies have considered specific habitat changes that might result from natural vegetation processes or from perturbations of vegetation. The role of large-scale habitat change induced by natural successional change from forest to bog (paludification) is examined and how large perturbations (e.g., volcanism, bolide impacts) might favor increased rates of paludification and consequent mass extinctions is considered. This hypothesis has an advantage over other hypotheses for mass extinctions in that modern day analogs of paludification are common throughout the world, thus allowing for considerable testing.

  18. Microbes and mass extinctions: paleoenvironmental distribution of microbialites during times of biotic crisis.

    PubMed

    Mata, S A; Bottjer, D J

    2012-01-01

    Widespread development of microbialites characterizes the substrate and ecological response during the aftermath of two of the 'big five' mass extinctions of the Phanerozoic. This study reviews the microbial response recorded by macroscopic microbial structures to these events to examine how extinction mechanism may be linked to the style of microbialite development. Two main styles of response are recognized: (i) the expansion of microbialites into environments not previously occupied during the pre-extinction interval and (ii) increases in microbialite abundance and attainment of ecological dominance within environments occupied prior to the extinction. The Late Devonian biotic crisis contributed toward the decimation of platform margin reef taxa and was followed by increases in microbialite abundance in Famennian and earliest Carboniferous platform interior, margin, and slope settings. The end-Permian event records the suppression of infaunal activity and an elimination of metazoan-dominated reefs. The aftermath of this mass extinction is characterized by the expansion of microbialites into new environments including offshore and nearshore ramp, platform interior, and slope settings. The mass extinctions at the end of the Triassic and Cretaceous have not yet been associated with a macroscopic microbial response, although one has been suggested for the end-Ordovician event. The case for microbialites behaving as 'disaster forms' in the aftermath of mass extinctions accurately describes the response following the Late Devonian and end-Permian events, and this may be because each is marked by the reduction of reef communities in addition to a suppression of bioturbation related to the development of shallow-water anoxia. © 2011 Blackwell Publishing Ltd.

  19. The fossil record of evolution: Analysis of extinction

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1986-01-01

    There is increasing evidence that events in space have had direct effects on Earth history and on the history of life on Earth. Nowhere is this more evident than in mass extinction. The biosphere has undergone repeated devastation caused by relatively short-lived environmental stress, with species kill rates up to 80 and 95%. For five of the mass extinctions, geochemical or other evidence was reported suggesting large body impact as the cause of the environmental stress producing the extinctions. It was argued on statistical ground that the major extinction events are uniformly periodic in geological time. If it is true that large body impact is a principal cause of mass extinctions and if the periodicity is real, than a cosmic driving mechanism is inescapable. Paleontological data sets were developed which detail the ranges in geological time of about 4,000 families and 25,000 genera of fossil marine organisms. Analyses to date have concentrated on the most recent 250 million years. Associated with these studies are analyses of other aspects of Earth history which may have signatures indicative of extraterrestrial effects.

  20. Mass extinction caused by large bolide impacts

    NASA Technical Reports Server (NTRS)

    Alvarez, Luis W.

    1987-01-01

    A history and development status assessment is presented for the hypothesis that the great extinction of living species 65 million years ago, at the boundary between the Tertiary and Cretaceous geological ages, was due to the collision of a meteoroid, asteroid, or comet with the earth. The initial, deeply suggestive indication of the extraterrestial origin of the extinction-initiating mechanism was the detection of an exceptionally high concentration of iridium at the stratigraphic position of the extinction. Detailed computer modeling of the atmospheric effect of such a bolide impact has shown that the earth would have first grown intensely cold during a period of darkness due to particulate debris clouds in the upper atmosphere, followed by an enormous increase in global temperatures as the debris cleared, created by the persistence of greenhouse-effect gases; this heating would have been especially lethal to numerous forms of life.

  1. Is Global Anoxia an Alternative Cause for the Hirnantian Mass Extinction?

    NASA Astrophysics Data System (ADS)

    De Weirdt, Julie; Vandenbroucke, Thijs; Emsbo, Poul; McLaughlin, Patrick; Delabroye, Aurélien; Munnecke, Axel; Desrochers, André

    2017-04-01

    Cooling and glacial episodes have long been considered the main driver of Late Ordovician-Silurian (mass) extinction events that coincide with δ13Ccarb excursions. However, emerging evidence for protracted cooling during most of the Ordovician and the misalignment between major regressions and faunal turnovers in the Upper Ordovician, suggests a more complex relation between glaciations and extinctions. Emsbo et al. (2010, GSA Abstracts with Programs) demonstrated dramatic enrichments in redox sensitive metals during the early Wenlock Ireviken extinction event and suggested ocean anoxia as an alternative kill-mechanism. Vandenbroucke et al. (2015, Nature Communications), built on this idea and recorded a similar increase of redox-sensitive metals at the onset of the mid-Pridoli extinction event, coinciding with peak abundances of malformed (teratological) fossil microplankton (acritarchs and chitinozoans). By analogy with metal-induced malformations in modern marine microplankton, teratology might serve as an independent proxy for monitoring changes in the metal concentration of the Palaeozoic ocean. These data from the Ireviken and Pridoli events are the foundation for the hypothesis that many, if not all, of these Late Ordovician-Silurian extinctions are caused by large-scale 'oceanic anoxic events'. Here, we are testing this hypothesis for the most devastating extinction event in this series, the Hirnantian mass extinction. Bulk rock samples spanning the Hirnantian strata of Anticosti Island were geochemically analysed. Our choice of sections is guided by the presence of teratological acritarchs (Delabroye et al., 2012, Rev. Pal. Pal.) that overlap the base of the extinction horizon. Revealing similar results as in our the previous studies, the new XRF data show distinct peaks in redox sensitive metals, supporting ocean anoxia and metal pollution as an important factor in the Hirnantian extinction, if not its fundamental cause.

  2. Provincialization of terrestrial faunas following the end-Permian mass extinction.

    PubMed

    Sidor, Christian A; Vilhena, Daril A; Angielczyk, Kenneth D; Huttenlocker, Adam K; Nesbitt, Sterling J; Peecook, Brandon R; Steyer, J Sébastien; Smith, Roger M H; Tsuji, Linda A

    2013-05-14

    In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ∼257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ∼242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic.

  3. Provincialization of terrestrial faunas following the end-Permian mass extinction

    PubMed Central

    Sidor, Christian A.; Vilhena, Daril A.; Angielczyk, Kenneth D.; Huttenlocker, Adam K.; Nesbitt, Sterling J.; Peecook, Brandon R.; Steyer, J. Sébastien; Smith, Roger M. H.; Tsuji, Linda A.

    2013-01-01

    In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ∼257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ∼242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic. PMID:23630295

  4. Mass Extinction and the Structure of the Milky Way

    NASA Astrophysics Data System (ADS)

    Filipovic, M. D.; Horner, J.; Crawford, E. J.; Tothill, N. F. H.; White, G. L.

    2013-12-01

    We use the most up-to-date Milky Way model and solar orbit data in order to test the hypothesis that the Sun's galactic spiral arm crossings cause mass extinction events on Earth. To do this, we created a new model of the Milky Way's spiral arms by combining a large quantity of data from several surveys. We then combined this model with a recently derived solution for the solar orbit to determine the timing of the Sun's historical passages through the Galaxy's spiral arms. Our new model was designed with a symmetrical appearance, with the major alteration being the addition of a spur at the far side of the Galaxy. A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33~Myr ago. Our simulations indicate that the Sun has spent ˜60 per cent of its time passing through our Galaxy's various spiral arms. Also, we briefly discuss and combine previous work on the Galactic Habitable Zone with the new Milky Way model.

  5. The fossil record of evolution: Data on diversification and extinction

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J., Jr.

    1986-01-01

    Synoptic studies of the fossil record of complex life on Earth indicate increasingly that extinction, and especially mass extinction, were extremely important driving forces in the history of life. Analysis of a new compilation of geologic ranges for 25,000 genera of marine animals suggests that extinction events were much more frequent in occurrence and variable in magnitude than previously suspected. At least 30 well documented and potential mass extinctions were identified in the dataset. The most recent event, distributed over 260 to 0 ma. exhibit a stationary periodicity of 26.1 + or - 1 ma, implicating a cosmological forcing mechanism. Earlier events, especially in the 575 to 450 ma interval, are more frequent, possibly indicating either a breakdown of periodicity in the more distant past; and as yet undemonstrated diminution of the period length; or frequent aperiodic terrestrial perturbations of a less stable biota superimposed upon the cosmological periodicity.

  6. Quantifying ecological impacts of mass extinctions with network analysis of fossil communities

    PubMed Central

    Muscente, A. D.; Prabhu, Anirudh; Zhong, Hao; Eleish, Ahmed; Meyer, Michael B.; Fox, Peter; Hazen, Robert M.; Knoll, Andrew H.

    2018-01-01

    Mass extinctions documented by the fossil record provide critical benchmarks for assessing changes through time in biodiversity and ecology. Efforts to compare biotic crises of the past and present, however, encounter difficulty because taxonomic and ecological changes are decoupled, and although various metrics exist for describing taxonomic turnover, no methods have yet been proposed to quantify the ecological impacts of extinction events. To address this issue, we apply a network-based approach to exploring the evolution of marine animal communities over the Phanerozoic Eon. Network analysis of fossil co-occurrence data enables us to identify nonrandom associations of interrelated paleocommunities. These associations, or evolutionary paleocommunities, dominated total diversity during successive intervals of relative community stasis. Community turnover occurred largely during mass extinctions and radiations, when ecological reorganization resulted in the decline of one association and the rise of another. Altogether, we identify five evolutionary paleocommunities at the generic and familial levels in addition to three ordinal associations that correspond to Sepkoski’s Cambrian, Paleozoic, and Modern evolutionary faunas. In this context, we quantify magnitudes of ecological change by measuring shifts in the representation of evolutionary paleocommunities over geologic time. Our work shows that the Great Ordovician Biodiversification Event had the largest effect on ecology, followed in descending order by the Permian–Triassic, Cretaceous–Paleogene, Devonian, and Triassic–Jurassic mass extinctions. Despite its taxonomic severity, the Ordovician extinction did not strongly affect co-occurrences of taxa, affirming its limited ecological impact. Network paleoecology offers promising approaches to exploring ecological consequences of extinctions and radiations. PMID:29686079

  7. Quantifying ecological impacts of mass extinctions with network analysis of fossil communities.

    PubMed

    Muscente, A D; Prabhu, Anirudh; Zhong, Hao; Eleish, Ahmed; Meyer, Michael B; Fox, Peter; Hazen, Robert M; Knoll, Andrew H

    2018-05-15

    Mass extinctions documented by the fossil record provide critical benchmarks for assessing changes through time in biodiversity and ecology. Efforts to compare biotic crises of the past and present, however, encounter difficulty because taxonomic and ecological changes are decoupled, and although various metrics exist for describing taxonomic turnover, no methods have yet been proposed to quantify the ecological impacts of extinction events. To address this issue, we apply a network-based approach to exploring the evolution of marine animal communities over the Phanerozoic Eon. Network analysis of fossil co-occurrence data enables us to identify nonrandom associations of interrelated paleocommunities. These associations, or evolutionary paleocommunities, dominated total diversity during successive intervals of relative community stasis. Community turnover occurred largely during mass extinctions and radiations, when ecological reorganization resulted in the decline of one association and the rise of another. Altogether, we identify five evolutionary paleocommunities at the generic and familial levels in addition to three ordinal associations that correspond to Sepkoski's Cambrian, Paleozoic, and Modern evolutionary faunas. In this context, we quantify magnitudes of ecological change by measuring shifts in the representation of evolutionary paleocommunities over geologic time. Our work shows that the Great Ordovician Biodiversification Event had the largest effect on ecology, followed in descending order by the Permian-Triassic, Cretaceous-Paleogene, Devonian, and Triassic-Jurassic mass extinctions. Despite its taxonomic severity, the Ordovician extinction did not strongly affect co-occurrences of taxa, affirming its limited ecological impact. Network paleoecology offers promising approaches to exploring ecological consequences of extinctions and radiations. Copyright © 2018 the Author(s). Published by PNAS.

  8. DO PERIODICITIES IN EXTINCTION-WITH POSSIBLE ASTRONOMICAL CONNECTIONS-SURVIVE A REVISION OF THE GEOLOGICAL TIMESCALE?

    SciTech Connect

    Melott, Adrian L.; Bambach, Richard K.

    A major revision of the geological timescale was published in 2012. We re-examine our past finding of a 27 Myr periodicity in marine extinction rates by re-assigning dates to the extinction data used previously. We find that the spectral power in this period is somewhat increased, and persists at a narrow bandwidth, which supports our previous contention that the Nemesis hypothesis is untenable as an explanation for the periodicity that was first noted by Raup and Sepkoski in the 1980s. We enumerate a number of problems in a recent study comparing extinction rates with time series models.

  9. A Cretaceous-Tertiary mass extinction? Were most of Earth's species killed off?

    NASA Technical Reports Server (NTRS)

    Briggs, J. C.

    1991-01-01

    For the past decade, the scientific and popular press have carried frequent articles about a catastrophic mass extinction that supposedly destroyed the majority of the earth's species, including the dinosaurs, approximately 65 million years ago. Since 1980, more than 2000 papers and books have dealt with some aspect of a mass extinction at the Cretaceous-Tertiary (K/T) boundary. One authoritative estimate of the severity of the extinctions is that 60-80% of all the living species became extinct at this boundary (Raup 1988). There appears to be a general acceptance of the fact that such a great catastrophe did occur. Most of the argument among scientists now is devoted to the determination of the cause. In this article, I argue that the species changes at the K/T boundary were neither sudden nor catastrophic. They were most likely caused by a regression of sea level that led to a decrease in primary production.

  10. Triassic–Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs

    PubMed Central

    Toljagić, Olja; Butler, Richard J.

    2013-01-01

    Pseudosuchia, one of the two main clades of Archosauria (Reptilia: Diapsida), suffered a major decline in lineage diversity during the Triassic–Jurassic (TJ) mass extinction (approx. 201 Ma). Crocodylomorpha, including living crocodilians and their extinct relatives, is the only group of pseudosuchians that survived into the Jurassic. We reassess changes in pseudosuchian morphological diversity (disparity) across this time interval, using considerably larger sample sizes than in previous analyses. Our results show that metrics of pseudosuchian disparity did not change significantly across the TJ boundary, contrasting with previous work suggesting low pseudosuchian disparity in the Early Jurassic following the TJ mass extinction. However, a significant shift in morphospace occupation between Late Triassic and Early Jurassic taxa is recognized, suggesting that the TJ extinction of many pseudosuchian lineages was followed by a major and geologically rapid adaptive radiation of crocodylomorphs. This marks the onset of the spectacularly successful evolutionary history of crocodylomorphs in Jurassic and Cretaceous ecosystems. PMID:23536443

  11. Body size reductions in nonmammalian eutheriodont therapsids (Synapsida) during the end-Permian mass extinction.

    PubMed

    Huttenlocker, Adam K

    2014-01-01

    The extent to which mass extinctions influence body size evolution in major tetrapod clades is inadequately understood. For example, the 'Lilliput effect,' a common feature of mass extinctions, describes a temporary decrease in body sizes of survivor taxa in post-extinction faunas. However, its signature on existing patterns of body size evolution in tetrapods and the persistence of its impacts during post-extinction recoveries are virtually unknown, and rarely compared in both geologic and phylogenetic contexts. Here, I evaluate temporal and phylogenetic distributions of body size in Permo-Triassic therocephalian and cynodont therapsids (eutheriodonts) using a museum collections-based approach and time series model fitting on a regional stratigraphic sequence from the Karoo Basin, South Africa. I further employed rank order correlation tests on global age and clade rank data from an expanded phylogenetic dataset, and performed evolutionary model testing using Brownian (passive diffusion) models. Results support significant size reductions in the immediate aftermath of the end-Permian mass extinction (ca. 252.3 Ma) consistent with some definitions of Lilliput effects. However, this temporal succession reflects a pattern that was underscored largely by Brownian processes and constructive selectivity. Results also support two recent contentions about body size evolution and mass extinctions: 1) active, directional evolution in size traits is rare over macroevolutionary time scales and 2) geologically brief size reductions may be accomplished by the ecological removal of large-bodied species without rapid originations of new small-bodied clades or shifts from long-term evolutionary patterns.

  12. Global microbial carbonate proliferation after the end-Devonian mass extinction: Mainly controlled by demise of skeletal bioconstructors

    PubMed Central

    Yao, Le; Aretz, Markus; Chen, Jitao; Webb, Gregory E.; Wang, Xiangdong

    2016-01-01

    Microbial carbonates commonly flourished following mass extinction events. The end-Devonian (Hangenberg) mass extinction event is a first-order mass extinction on the scale of the ‘Big Five’ extinctions. However, to date, it is still unclear whether global microbial carbonate proliferation occurred after the Hangenberg event. The earliest known Carboniferous stromatolites on tidal flats are described from intertidal environments of the lowermost Tournaisian (Qianheishan Formation) in northwestern China. With other early Tournaisian microbe-dominated bioconstructions extensively distributed on shelves, the Qianheishan stromatolites support microbial carbonate proliferation after the Hangenberg extinction. Additional support comes from quantitative analysis of the abundance of microbe-dominated bioconstructions through the Famennian and early Tournaisian, which shows that they were globally distributed (between 40° latitude on both sides of the palaeoequator) and that their abundance increased distinctly in the early Tournaisian compared to the latest Devonian (Strunian). Comparison of variations in the relative abundance of skeleton- versus microbe-dominated bioconstructions across the Hangenberg and ‘Big Five’ extinctions suggests that changes in abundance of skeletal bioconstructors may play a first-order control on microbial carbonate proliferation during extinction transitions but that microbial proliferation is not a general necessary feature after mass extinctions. PMID:28009013

  13. Impact-driven ocean acidification as a mechanism of the Cretaceous-Palaeogene mass extinction

    NASA Astrophysics Data System (ADS)

    Ohno, S.; Kadono, T.; Kurosawa, K.; Hamura, T.; Sakaiya, T.; Shigemori, K.; Hironaka, Y.; Sano, T.; Watari, T.; Otani, K.; Matsui, T.; Sugita, S.

    2014-12-01

    The Cretaceous-Paleogene (K-Pg) mass extinction event at 66 Ma triggered by a meteorite impact is one of the most drastic events in the history of life on the Earth. Many hypotheses have been proposed as killing mechanisms induced by the impact, including global darkness due to high concentrations of atmospheric silicate dust particles, global wildfires, greenhouse warming due to CO2 release, and global acid rain. However, the actual mechanism of extinction remains highly controversial. One of the most important clues for understanding the extinction mechanism is the marine plankton record, which indicates that plankton foraminifera, living in the near-surface ocean, suffered very severe extinction in contrast to the high survival ratio of benthic foraminifera. No proposed extinction mechanism can account for this globally observed marine extinction pattern. Here, we show that SO3-rich impact vapor was released in the K-Pg impact and resulted in the occurrence of global acid rain and sudden severe ocean acidification at the end of the Cretaceous, based on the new results of impact experiments at velocities much higher than previous works (> 10 km/s) and theoretical calculations on aerosol coagulation processes. Sudden severe ocean acidification can account for many of the features of various geologic records at the K?Pg boundary, including severe extinction of plankton foraminifera. This extinction mechanism requires impact degassing of SO3-rich vapor, which is not necessarily found at impact sites other than Chicxulub, suggesting that the degree of mass extinction was controlled greatly by target lithology.

  14. Body Size Reductions in Nonmammalian Eutheriodont Therapsids (Synapsida) during the End-Permian Mass Extinction

    PubMed Central

    Huttenlocker, Adam K.

    2014-01-01

    The extent to which mass extinctions influence body size evolution in major tetrapod clades is inadequately understood. For example, the ‘Lilliput effect,’ a common feature of mass extinctions, describes a temporary decrease in body sizes of survivor taxa in post-extinction faunas. However, its signature on existing patterns of body size evolution in tetrapods and the persistence of its impacts during post-extinction recoveries are virtually unknown, and rarely compared in both geologic and phylogenetic contexts. Here, I evaluate temporal and phylogenetic distributions of body size in Permo-Triassic therocephalian and cynodont therapsids (eutheriodonts) using a museum collections-based approach and time series model fitting on a regional stratigraphic sequence from the Karoo Basin, South Africa. I further employed rank order correlation tests on global age and clade rank data from an expanded phylogenetic dataset, and performed evolutionary model testing using Brownian (passive diffusion) models. Results support significant size reductions in the immediate aftermath of the end-Permian mass extinction (ca. 252.3 Ma) consistent with some definitions of Lilliput effects. However, this temporal succession reflects a pattern that was underscored largely by Brownian processes and constructive selectivity. Results also support two recent contentions about body size evolution and mass extinctions: 1) active, directional evolution in size traits is rare over macroevolutionary time scales and 2) geologically brief size reductions may be accomplished by the ecological removal of large-bodied species without rapid originations of new small-bodied clades or shifts from long-term evolutionary patterns. PMID:24498335

  15. A Unified Theory of Impact Crises and Mass Extinctions: Quantitative Tests

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Haggerty, Bruce M.; Pagano, Thomas C.

    1997-01-01

    Several quantitative tests of a general hypothesis linking impacts of large asteroids and comets with mass extinctions of life are possible based on astronomical data, impact dynamics, and geological information. The waiting of large-body impacts on the Earth derive from the flux of Earth-crossing asteroids and comets, and the estimated size of impacts capable of causing large-scale environmental disasters, predict that impacts of objects greater than or equal to 5 km in diameter (greater than or equal to 10 (exp 7) Mt TNT equivalent) could be sufficient to explain the record of approximately 25 extinction pulses in the last 540 Myr, with the 5 recorded major mass extinctions related to impacts of the largest objects of greater than or equal to 10 km in diameter (greater than or equal to 10(exp 8) Mt Events). Smaller impacts (approximately 10 (exp 6) Mt), with significant regional environmental effects, could be responsible for the lesser boundaries in the geologic record.

  16. Flood-Basalt Eruptions and Extraterrestrial Impacts Linked to Mass-Extinction Events and Times of Ocean Anoxia of the Past 260 Myr

    NASA Astrophysics Data System (ADS)

    Rampino, M. R.

    2017-12-01

    Correlations among impacts, flood-basalt episodes, extinctions and ocean anoxic events have been proposed. A closer look at the data, shows 13 documented extinction events over the last 260 Myr, 12 of which coincide, within errors, with the ages of flood-basalt eruptions (8 events) or large impacts (6 events) (Figure 1). The null hypothesis that this could occur by chance can be rejected with >99.99% confidence. Large impacts (craters >70 km in diameter) coincide with extinction events at 36 (two impacts), 66, 145, 168 (?) and 215 Myr ago. The ages of flood basalts coincide with extinctions at 66, 94, 118, 133 (?), 183, 201, 252, and 259 Myr ago (Figure 1). Only the age of the K-Pg boundary at 66 Myr is known to correlate with both a large impact and a flood-basalt province, which may help explain the severity of that mass extinction. The age of the North Atlantic Volcanic Province Basalts (56 Myr ago), while not marked by an extinction event, coincides with the PETM climatic episode. Furthermore, at least 7 periods with evidence of anoxia in the oceans in the last 260 Myr coincide with the ages of flood-basalt eruptions (with >99.99% confidence), and are also coeval with extinction events, suggesting a causal connection (Figure 1). These statistical relationships argue that most mass extinction events are related to environmental catastrophes produced by large-volume flood-basalt eruptions and large asteroid or comet impacts.

  17. Flourishing ocean drives the end-Permian marine mass extinction

    PubMed Central

    Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

    2015-01-01

    The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian−Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth’s history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness. PMID:26240323

  18. Flourishing ocean drives the end-Permian marine mass extinction.

    PubMed

    Schobben, Martin; Stebbins, Alan; Ghaderi, Abbas; Strauss, Harald; Korn, Dieter; Korte, Christoph

    2015-08-18

    The end-Permian mass extinction, the most severe biotic crisis in the Phanerozoic, was accompanied by climate change and expansion of oceanic anoxic zones. The partitioning of sulfur among different exogenic reservoirs by biological and physical processes was of importance for this biodiversity crisis, but the exact role of bioessential sulfur in the mass extinction is still unclear. Here we show that globally increased production of organic matter affected the seawater sulfate sulfur and oxygen isotope signature that has been recorded in carbonate rock spanning the Permian-Triassic boundary. A bifurcating temporal trend is observed for the strata spanning the marine mass extinction with carbonate-associated sulfate sulfur and oxygen isotope excursions toward decreased and increased values, respectively. By coupling these results to a box model, we show that increased marine productivity and successive enhanced microbial sulfate reduction is the most likely scenario to explain these temporal trends. The new data demonstrate that worldwide expansion of euxinic and anoxic zones are symptoms of increased biological carbon recycling in the marine realm initiated by global warming. The spatial distribution of sulfidic water column conditions in shallow seafloor environments is dictated by the severity and geographic patterns of nutrient fluxes and serves as an adequate model to explain the scale of the marine biodiversity crisis. Our results provide evidence that the major biodiversity crises in Earth's history do not necessarily implicate an ocean stripped of (most) life but rather the demise of certain eukaryotic organisms, leading to a decline in species richness.

  19. Mercury anomalies and the timing of biotic recovery following the end-Triassic mass extinction

    PubMed Central

    Thibodeau, Alyson M.; Ritterbush, Kathleen; Yager, Joyce A.; West, A. Joshua; Ibarra, Yadira; Bottjer, David J.; Berelson, William M.; Bergquist, Bridget A.; Corsetti, Frank A.

    2016-01-01

    The end-Triassic mass extinction overlapped with the eruption of the Central Atlantic Magmatic Province (CAMP), and release of CO2 and other volcanic volatiles has been implicated in the extinction. However, the timing of marine biotic recovery versus CAMP eruptions remains uncertain. Here we use Hg concentrations and isotopes as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. In Triassic–Jurassic strata, Muller Canyon, Nevada, Hg levels rise in the extinction interval, peak before the appearance of the first Jurassic ammonite, remain above background in association with a depauperate fauna, and fall to pre-extinction levels during significant pelagic and benthic faunal recovery. Hg isotopes display no significant mass independent fractionation within the extinction and depauperate intervals, consistent with a volcanic origin for the Hg. The Hg and palaeontological evidence from the same archive indicate that significant biotic recovery did not begin until CAMP eruptions ceased. PMID:27048776

  20. Earth's biggest 'whodunnit': unravelling the clues in the case of the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    White, Rosalind V.

    2002-12-01

    The mass extinction that occurred at the end of the Permian period, 250 million years ago, was the most devastating loss of life that Earth has ever experienced. It is estimated that ca.96% of marine species were wiped out and land plants, reptiles, amphibians and insects also suffered. The causes of this catastrophic event are currently a topic of intense debate. The geological record points to significant environmental disturbances, for example, global warming and stagnation of ocean water. A key issue is whether the Earth's feedback mechanisms can become unstable on their own, or whether some forcing is required to precipitate a catastrophe of this magnitude. A prime suspect for pushing Earth's systems into a critical condition is massive end-Permian Siberian volcanism, which would have pumped large quantities of carbon dioxide and toxic gases into the atmosphere. Recently, it has been postulated that Earth was also the victim of a bolide impact at this time. If further research substantiates this claim, it raises some intriguing questions. The Cretaceous-Tertiary mass extinction, 65 million years ago, was contemporaneous with both an impact and massive volcanism. Are both types of calamity necessary to drive Earth to the brink of faunal cataclysm? We do not presently have enough pieces of the jigsaw to solve the mystery of the end-Permian extinction, but the forensic work continues.

  1. Causes of the great mass extinction of marine organisms in the Late Devonian

    NASA Astrophysics Data System (ADS)

    Barash, M. S.

    2016-11-01

    The second of the five great mass extinctions of the Phanerozoic occurred in the Late Devonian. The number of species decreased by 70-82%. Major crises occurred at the Frasnian-Famennian and Devonian-Carboniferous boundary. The lithological and geochemical compositions of sediments, volcanic deposits, impactites, carbon and oxygen isotope ratios, evidence of climate variability, and sea level changes reflect the processes that led the critical conditions. Critical intervals are marked by layers of black shales, which were deposited in euxinic or anoxic environments. These conditions were the main direct causes of the extinctions. The Late Devonian mass extinction was determined by a combination of impact events and extensive volcanism. They produced similar effects: emissions of harmful chemical compounds and aerosols to cause greenhouse warming; darkening of the atmosphere, which prevented photosynthesis; and stagnation of oceans and development of anoxia. Food chains collapsed and biological productivity decreased. As a result, all vital processes were disturbed and a large portion of the biota became extinct.

  2. A stochastic model for the probability of malaria extinction by mass drug administration.

    PubMed

    Pemberton-Ross, Peter; Chitnis, Nakul; Pothin, Emilie; Smith, Thomas A

    2017-09-18

    Mass drug administration (MDA) has been proposed as an intervention to achieve local extinction of malaria. Although its effect on the reproduction number is short lived, extinction may subsequently occur in a small population due to stochastic fluctuations. This paper examines how the probability of stochastic extinction depends on population size, MDA coverage and the reproduction number under control, R c . A simple compartmental model is developed which is used to compute the probability of extinction using probability generating functions. The expected time to extinction in small populations after MDA for various scenarios in this model is calculated analytically. The results indicate that mass drug administration (Firstly, R c must be sustained at R c  < 1.2 to avoid the rapid re-establishment of infections in the population. Secondly, the MDA must produce effective cure rates of >95% to have a non-negligible probability of successful elimination. Stochastic fluctuations only significantly affect the probability of extinction in populations of about 1000 individuals or less. The expected time to extinction via stochastic fluctuation is less than 10 years only in populations less than about 150 individuals. Clustering of secondary infections and of MDA distribution both contribute positively to the potential probability of success, indicating that MDA would most effectively be administered at the household level. There are very limited circumstances in which MDA will lead to local malaria elimination with a substantial probability.

  3. Mid Pleistocene foraminiferal mass extinction coupled with phytoplankton evolution

    PubMed Central

    Kender, Sev; McClymont, Erin L.; Elmore, Aurora C.; Emanuele, Dario; Leng, Melanie J.; Elderfield, Henry

    2016-01-01

    Understanding the interaction between climate and biotic evolution is crucial for deciphering the sensitivity of life. An enigmatic mass extinction occurred in the deep oceans during the Mid Pleistocene, with a loss of over 100 species (20%) of sea floor calcareous foraminifera. An evolutionarily conservative group, benthic foraminifera often comprise >50% of eukaryote biomass on the deep-ocean floor. Here we test extinction hypotheses (temperature, corrosiveness and productivity) in the Tasman Sea, using geochemistry and micropalaeontology, and find evidence from several globally distributed sites that the extinction was caused by a change in phytoplankton food source. Coccolithophore evolution may have enhanced the seasonal ‘bloom' nature of primary productivity and fundamentally shifted it towards a more intra-annually variable state at ∼0.8 Ma. Our results highlight intra-annual variability as a potential new consideration for Mid Pleistocene global biogeochemical climate models, and imply that deep-sea biota may be sensitive to future changes in productivity. PMID:27311937

  4. Exposure to a fearful context during periods of memory plasticity impairs extinction via hyperactivation of frontal-amygdalar circuits

    PubMed Central

    Stafford, James M.; Maughan, DeeAnna K.; Ilioi, Elena C.; Lattal, K. Matthew

    2013-01-01

    An issue of increasing theoretical and translational importance is to understand the conditions under which learned fear can be suppressed, or even eliminated. Basic research has pointed to extinction, in which an organism is exposed to a fearful stimulus (such as a context) in the absence of an expected aversive outcome (such as a shock). This extinction process results in the suppression of fear responses, but is generally thought to leave the original fearful memory intact. Here, we investigate the effects of extinction during periods of memory lability on behavioral responses and on expression of the immediate–early gene c-Fos within fear conditioning and extinction circuits. Our results show that long-term extinction is impaired when it occurs during time periods during which the memory should be most vulnerable to disruption (soon after conditioning or retrieval). These behavioral effects are correlated with hyperactivation of medial prefrontal cortex and amygdala subregions associated with fear expression rather than fear extinction. These findings demonstrate that behavioral experiences during periods of heightened fear prevent extinction and prolong the conditioned fear response. PMID:23422280

  5. Evolutionary and Ecological Sequelae of Mass Extinctions: Examples From the Continental Triassic-Jurassic Boundary

    NASA Astrophysics Data System (ADS)

    Olsen, P. E.; Whiteside, J. H.

    2003-12-01

    The Triassic-Jurassic boundary at ˜200 Ma marks one of the five major mass-extinctions of the Phanerozoic and, depending on the metrics used, was similar in magnitude to the K-T mass extinction. In continental environments about 50% of all tetrapod families are eliminated and although floral diversity change is difficult to gauge, a similar proportion of palynomorph taxa disappear at the boundary. The extinction event appears to have been very abrupt, followed by a roughly 900 ky super-greenhouse period characterized by increased precipitation. We hypothesize a series of biological consequences of the drop in diversity and associated super-greenhouse based on observations of the earliest Jurassic assemblages, largely from eastern North America. 1) The drop in diversity results in a collapse of ecological interactions that tend to stabilize the composition of regional biotas and buffer them from invading forms. Triassic assemblages show considerable biogeographic provinciality despite the existence of Pangea, but the earliest Jurassic assemblages were extraordinarily homogenous with many vertebrate genera being essentially global in distribution. 2) Initially the post-boundary terrestrial assemblages were comprised of eurytopic trophic generalists, with animal communities with few herbivores, but abundant carnivores and detritivores subsisting on aquatic-based food webs. The earliest Jurassic tetrapod footprint record is overwhelmingly dominated by the footprints of ceratosaurian theropod dinosaurs, the latter having skull characteristics usually associated at least in part with piscivory. 3) The dramatic size changes over very short periods of time were likely due to an absence of competition (i.e., ecological release). The maximum size of theropod dinosaur footprints increased by about 25% within 10 ky following the boundary, corresponding to a doubling of mass. 4) Representatives of clades with intrinsically high rates of speciation tend to form species flocks

  6. Severe environmental effects of Chicxulub impact imply key role in end-Cretaceous mass extinction

    NASA Astrophysics Data System (ADS)

    Brugger, Julia; Feulner, Georg; Petri, Stefan

    2017-04-01

    66 million years ago, during the most recent of the five severe mass extinctions in Earth's history, non-avian dinosaurs and many other organisms became extinct. The cause of this end-Cretaceous mass extinction is seen in either flood-basalt eruptions or an asteroid impact. Modeling the climatic changes after the Chicxulub asteroid impact allow to assess its contribution to the extinction event and to analyze the short-term and long-term response of the climate and the biosphere to the impact. Existing studies either investigated the effect of dust, which is now believed to play a minor role, or used one-dimensional, non-coupled models. In contrast, we use a coupled climate model to explore the longer lasting cooling due to sulfate aerosols. Based on data from geophysical impact modeling, we set up simulations with different stratospheric residence times for sulfate aerosols. Depending on this residence time, global surface air temperature decreased by at least 26°C, with 3 to 16 years subfreezing temperatures and a recovery time larger than 30 years. Vigorous ocean mixing, caused by the fast cooling of the surface ocean, might have perturbed marine ecosystems by the upwelling of nutrients. The dramatic climatic changes seen in our simulations imply severe environmental effects and therefore a significant contribution of the impact in the end-Cretaceous mass extinction.

  7. The Arches Cluster Out to its Tidal Radius: Dynamical Mass Segregation and the Effect of the Extinction Law on the - Lar Mass Function

    NASA Astrophysics Data System (ADS)

    Habibi, Maryam; Stolte, Andrea; Brandner, Wolfgang; Hussman, Benjamin

    2013-07-01

    The Galactic Center is the most active site of star formation in the Milky Way Galaxy, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic Center through the Galactic disk, knowledge of extinction is crucial to study this region. The Arches cluster is a young, massive starburst cluster near the Galactic Center. We observed the Arches cluster out to its tidal radius using Ks-band imaging obtained with NAOS/CONICA at the VLT combined with Subaro/Cisco J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper-mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and ∆AKs˜1 magnitude in acquired Ks-band extinction, while the present mass function slope changes by ˜0.17 dex. The present-day mass function slope derived assuming the Nishiyama et al. (2009) extinction law increases from a flat slope of α-Nishi = 1.50 ± 0.35 in the core (r<0.2 pc) to α-Nishi = 2.21±0.27 in the intermediate annulus (0.2

  8. Macrofossil evidence for a rapid and severe Cretaceous-Paleogene mass extinction in Antarctica.

    PubMed

    Witts, James D; Whittle, Rowan J; Wignall, Paul B; Crame, J Alistair; Francis, Jane E; Newton, Robert J; Bowman, Vanessa C

    2016-05-26

    Debate continues about the nature of the Cretaceous-Paleogene (K-Pg) mass extinction event. An abrupt crisis triggered by a bolide impact contrasts with ideas of a more gradual extinction involving flood volcanism or climatic changes. Evidence from high latitudes has also been used to suggest that the severity of the extinction decreased from low latitudes towards the poles. Here we present a record of the K-Pg extinction based on extensive assemblages of marine macrofossils (primarily new data from benthic molluscs) from a highly expanded Cretaceous-Paleogene succession: the López de Bertodano Formation of Seymour Island, Antarctica. We show that the extinction was rapid and severe in Antarctica, with no significant biotic decline during the latest Cretaceous, contrary to previous studies. These data are consistent with a catastrophic driver for the extinction, such as bolide impact, rather than a significant contribution from Deccan Traps volcanism during the late Maastrichtian.

  9. Macrofossil evidence for a rapid and severe Cretaceous-Paleogene mass extinction in Antarctica

    NASA Astrophysics Data System (ADS)

    Witts, James D.; Whittle, Rowan J.; Wignall, Paul B.; Crame, J. Alistair; Francis, Jane E.; Newton, Robert J.; Bowman, Vanessa C.

    2016-05-01

    Debate continues about the nature of the Cretaceous-Paleogene (K-Pg) mass extinction event. An abrupt crisis triggered by a bolide impact contrasts with ideas of a more gradual extinction involving flood volcanism or climatic changes. Evidence from high latitudes has also been used to suggest that the severity of the extinction decreased from low latitudes towards the poles. Here we present a record of the K-Pg extinction based on extensive assemblages of marine macrofossils (primarily new data from benthic molluscs) from a highly expanded Cretaceous-Paleogene succession: the López de Bertodano Formation of Seymour Island, Antarctica. We show that the extinction was rapid and severe in Antarctica, with no significant biotic decline during the latest Cretaceous, contrary to previous studies. These data are consistent with a catastrophic driver for the extinction, such as bolide impact, rather than a significant contribution from Deccan Traps volcanism during the late Maastrichtian.

  10. Extinction and the fossil record

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; Sepkoski JJ, ,. J. r. (Principal Investigator)

    1994-01-01

    The author examines evidence of mass extinctions in the fossil record and searches for reasons for such large extinctions. Five major mass extinctions eliminated at least 40 percent of animal genera in the oceans and from 65 to 95 percent of ocean species. Questions include the occurrence of gradual or catastrophic extinctions, causes, environment, the capacity of a perturbation to cause extinctions each time it happens, and the possibility and identification of complex events leading to a mass extinction.

  11. Stellar orbits in the Galaxy and mass extinctions on the Earth: a connection?

    NASA Astrophysics Data System (ADS)

    Porto de Mello, G. F.; Dias, W. S.; Lepine, J.; Lorenzo-Oliveira, D.; Kazu, R. S.

    2014-03-01

    The orbits of the stars in the disk of the Galaxy, and their passages through the Galactic spiral arms, are a rarely mentioned factor of biosphere stability which might be important for long-term planetary climate evolution, with a possible bearing on mass extinctions. The Sun lies very near the co-rotation radius, where stars revolve around the Galaxy in the same period as the density wave perturbations of the spiral arms (Dias & Lepine 2005). Conventional wisdom generally considers that this status makes for few passages through the spiral arms. Controversy still surrounds whether time spent inside or around spiral arms is dangerous to biospheres and conducive to mass extinctions (Bailer-Jones 2009). Possible threats include giant molecular clouds disturbing the Oort comet cloud and provoking heavy bombardment (Clube & Napier 1982); a higher exposure to cosmic rays near star forming regions triggering increased cloudiness in Earth's atmosphere and ice ages (Gies & Helsel 2005); and the destruction of Earth's ozone layer posed by supernova explosions (Gehrels et al 2003). We present detailed calculations of the history of spiral arm passages for all 212 solartype stars nearer than 20 parsecs, including the total time spent inside the spiral arms in the last 500 million years, when the spiral arm position can be traced with good accuracy. There is a very large diversity of stellar orbits amongst solar neighborhood solar-type stars, and the time fraction spent inside spiral arms can vary from a few percent to nearly half the time. The Sun, despite its proximity to the galactic co-rotation radius, has exceptionally low eccentricity and a low vertical velocity component, and therefore spends 40% of its lifetime crossing the spiral arms, more than nearly all nearby stars. We discuss the possible implications of this fact to the long-term habitability of the Earth, and possible correlations of the Sun's passage through the spiral arms with the five great mass

  12. Mass extinctions, galactic orbits in the solar neighborhood and the Sun: a connection?

    NASA Astrophysics Data System (ADS)

    Porto de Mello, G. F.; Dias, W. S.; Lépine, J. R. D.; Lorenzo-Oliveira, D.; Siqueira, R. K.

    2014-10-01

    The orbits of the stars in the disk of the Galaxy, and their passages through the Galactic spiral arms, are a rarely mentioned factor of biosphere stability which might be important for long-term planetary climate evolution, with a possible bearing on mass extinctions. The Sun lies very near the co-rotation radius, where stars revolve around the Galaxy in the same period as the density wave perturbations of the spiral arms. Conventional wisdom generally considers that this status makes for few passages through the spiral arms. Controversy still surrounds whether time spent inside or around spiral arms is dangerous to biospheres and conducive to mass extinctions. Possible threats include giant molecular clouds disturbing the Oort comet cloud and provoking heavy bombardment; a higher exposure to cosmic rays near star forming regions triggering increased cloudiness in Earth's atmosphere and ice ages; and the destruction of Earth's ozone layer posed by supernova explosions. We present detailed calculations of the history of spiral arm passages for all 212 solar-type stars nearer than 20 parsecs, including the total time spent inside the spiral arms in the last 500 Myr, when the spiral arm position can be traced with good accuracy. We found that there is a large diversity of stellar orbits in the solar neighborhood, and the time fraction spent inside spiral arms can vary from a few percent to nearly half the time. The Sun, despite its proximity to the galactic co-rotation radius, has exceptionally low eccentricity and a low vertical velocity component, and therefore spends 30% of its lifetime crossing the spiral arms, more than most nearby stars. We discuss the possible implications of this fact to the long-term habitability of the Earth, and possible correlations of the Sun's passage through the spiral arms with the five great mass extinctions of the Earth's biosphere from the Late Ordovician to the Cretaceous-Tertiary.

  13. A general theory of impacts and mass extinctions, and the consequences of large-body impact on the Earth

    NASA Technical Reports Server (NTRS)

    Rampino, M. R.

    1994-01-01

    The theory that large-body impacts are the primary cause of mass extinctions of life on the Earth now has a sound theoretical and observational foundation. A convergence of evidence suggests that the biosphere may be a sensitive detector of large impact events, which result in the recorded global mass extinction pulses. The astronomically observed flux of asteroids and comets in the neighborhood of the Earth, and the threshold impact size calculated to produce a global environment catastrophe, can be used to predict a time history of large impact events and related mass extinctions of life that agrees well with the record of approx. 24 extinction events in the last 540 m.y.

  14. Macrofossil evidence for a rapid and severe Cretaceous–Paleogene mass extinction in Antarctica

    PubMed Central

    Witts, James D.; Whittle, Rowan J.; Wignall, Paul B.; Crame, J. Alistair; Francis, Jane E.; Newton, Robert J.; Bowman, Vanessa C.

    2016-01-01

    Debate continues about the nature of the Cretaceous–Paleogene (K–Pg) mass extinction event. An abrupt crisis triggered by a bolide impact contrasts with ideas of a more gradual extinction involving flood volcanism or climatic changes. Evidence from high latitudes has also been used to suggest that the severity of the extinction decreased from low latitudes towards the poles. Here we present a record of the K–Pg extinction based on extensive assemblages of marine macrofossils (primarily new data from benthic molluscs) from a highly expanded Cretaceous–Paleogene succession: the López de Bertodano Formation of Seymour Island, Antarctica. We show that the extinction was rapid and severe in Antarctica, with no significant biotic decline during the latest Cretaceous, contrary to previous studies. These data are consistent with a catastrophic driver for the extinction, such as bolide impact, rather than a significant contribution from Deccan Traps volcanism during the late Maastrichtian. PMID:27226414

  15. Evaluating the temporal link between Siberian Traps magmatism and the end-Permian mass extinction (Invited)

    NASA Astrophysics Data System (ADS)

    Burgess, S. D.; Bowring, S. A.

    2013-12-01

    Interest in Large Igneous Provinces as agents for massive climatic and biological change is steadily increasing, though the temporal constraints on both are seldom precise enough to allow detailed testing of a causal relationship. The end-Permian mass extinction is one of the most biologically important and intensely studied events in Earth history and has been linked to many possible trigger mechanisms, from voluminous volcanism to bolide impact. Proposed kill mechanisms range from acidic and/or anoxic oceans to a cocktail of toxic gases, although the link between trigger and kill mechanisms is unconstrained due to the lack of a high-precision timeline. Critical to assessing the plausibility of different trigger and kill mechanisms is an accurate age model for the biotic crisis and the perturbations to the global carbon cycle and ocean chemistry. Recent work using the EARTHTIME U/Pb tracer solution has refined the timing of the onset and duration of the marine mass extinction event and the earliest Triassic recovery at the GSSP for the Permian-Triassic boundary in Meishan, China. This work constrains the mass extinction duration to less than 100 kyr and provides an accurate and precise time point for the onset of extinction, against which the timing of potential trigger mechanisms may be compared. For more than two decades, eruption and emplacement of the Siberian traps has been implicated as a potential trigger of the end-Permian extinction. In this scenario, magmatism drives the biotic crisis through mobilization of volatiles from the sedimentary rock with which intruding and erupting magmas interact. Massive volatile release is believed to trigger major changes in atmospheric chemistry and temperature, both of which have been proposed as kill mechanisms. Current temporal constrains on the timing and duration of the Siberian magmatism are an order of magnitude less precise than those for the mass extinction event and associated environmental perturbations

  16. Mass extinction in poorly known taxa.

    PubMed

    Régnier, Claire; Achaz, Guillaume; Lambert, Amaury; Cowie, Robert H; Bouchet, Philippe; Fontaine, Benoît

    2015-06-23

    Since the 1980s, many have suggested we are in the midst of a massive extinction crisis, yet only 799 (0.04%) of the 1.9 million known recent species are recorded as extinct, questioning the reality of the crisis. This low figure is due to the fact that the status of very few invertebrates, which represent the bulk of biodiversity, have been evaluated. Here we show, based on extrapolation from a random sample of land snail species via two independent approaches, that we may already have lost 7% (130,000 extinctions) of the species on Earth. However, this loss is masked by the emphasis on terrestrial vertebrates, the target of most conservation actions. Projections of species extinction rates are controversial because invertebrates are essentially excluded from these scenarios. Invertebrates can and must be assessed if we are to obtain a more realistic picture of the sixth extinction crisis.

  17. Mass extinction in poorly known taxa

    PubMed Central

    Régnier, Claire; Achaz, Guillaume; Lambert, Amaury; Cowie, Robert H.; Bouchet, Philippe; Fontaine, Benoît

    2015-01-01

    Since the 1980s, many have suggested we are in the midst of a massive extinction crisis, yet only 799 (0.04%) of the 1.9 million known recent species are recorded as extinct, questioning the reality of the crisis. This low figure is due to the fact that the status of very few invertebrates, which represent the bulk of biodiversity, have been evaluated. Here we show, based on extrapolation from a random sample of land snail species via two independent approaches, that we may already have lost 7% (130,000 extinctions) of the species on Earth. However, this loss is masked by the emphasis on terrestrial vertebrates, the target of most conservation actions. Projections of species extinction rates are controversial because invertebrates are essentially excluded from these scenarios. Invertebrates can and must be assessed if we are to obtain a more realistic picture of the sixth extinction crisis. PMID:26056308

  18. Evidence of constant diversification punctuated by a mass extinction in the African cycads

    PubMed Central

    Yessoufou, Kowiyou; Bamigboye, Samuel O; Daru, Barnabas H; van der Bank, Michelle

    2014-01-01

    The recent evidence that extant cycads are not living fossils triggered a renewed search for a better understanding of their evolutionary history. In this study, we investigated the evolutionary diversification history of the genus Encephalartos, a monophyletic cycad endemic to Africa. We found an antisigmoidal pattern with a plateau and punctual explosive radiation. This pattern is typical of a constant radiation with mass extinction. The rate shift that we found may therefore be a result of a rapid recolonization of niches that have been emptied owing to mass extinction. Because the explosive radiation occurred during the transition Pliocene–Pleistocene, we argued that the processes might have been climatically mediated. PMID:24455160

  19. Repeated Carbon-Cycle Disturbances at the Permian-Triassic Boundary Separate two Mass Extinctions

    NASA Astrophysics Data System (ADS)

    Nicol, J. A.; Watson, L.; Claire, M.; Buick, R.; Catling, D. C.

    2004-12-01

    Non-marine organic matter in Permian-Triassic sediments from the Blue Mountains, eastern Australia shows seven negative δ13C excursions of up to 7%, terminating with a positive excursion of 4%. Fluctuations start at the late Permian Glossopteris floral extinction and continue until just above the palynological Permian-Triassic boundary, correlated with the peak of marine mass extinction. The isotopic fluctuations are not linked to changes in depositional setting, kerogen composition or plant community, so they evidently resulted from global perturbations in atmospheric δ13C and/or CO2. The pattern was not produced by a single catastrophe such as a meteorite impact, and carbon-cycle calculations indicate that gas release during flood-basalt volcanism was insufficient. Methane-hydrate melting can generate a single -7% shift, but cannot produce rapid multiple excursions without repeated reservoir regeneration and release. However, the data are consistent with repeated overturning of a stratified ocean, expelling toxic gases that promoted sequential mass extinctions in the terrestrial and marine realms.

  20. Organic-Chemical Clues to the Theory of Impacts as a Cause of Mass Extinctions

    NASA Astrophysics Data System (ADS)

    Sack, N. J.

    1988-11-01

    The reasons for the mass extinctions, which occur from time to time in Earth's history-as, e.g., the dinosaur extinction at the Cretaceous/Tertiary boundary 65 myr ago - are still not satisfactorily cleared up. A possible reason might be the impact of one or several comets of several kilometers in diameter. In this paper the astrophysical background of this hypothesis and organic-chemical processes during an impact will be discussed. Quantitative estimations are given, which show that the amount of organic substances brought to the Earth may be of the same order of magnitude as the normal biological production of organic material. Investigations are proposed to examine the organic-chemical composition of profiles of the Cretaceous/Tertiary boundary and other boundaries, at which mass extinction had occurred, in order to find anomalies as consequences of impacts.

  1. Timing and pacing of the Late Devonian mass extinction event regulated by eccentricity and obliquity.

    PubMed

    De Vleeschouwer, David; Da Silva, Anne-Christine; Sinnesael, Matthias; Chen, Daizhao; Day, James E; Whalen, Michael T; Guo, Zenghui; Claeys, Philippe

    2017-12-22

    The Late Devonian envelops one of Earth's big five mass extinction events at the Frasnian-Famennian boundary (374 Ma). Environmental change across the extinction severely affected Devonian reef-builders, besides many other forms of marine life. Yet, cause-and-effect chains leading to the extinction remain poorly constrained as Late Devonian stratigraphy is poorly resolved, compared to younger cataclysmic intervals. In this study we present a global orbitally calibrated chronology across this momentous interval, applying cyclostratigraphic techniques. Our timescale stipulates that 600 kyr separate the lower and upper Kellwasser positive δ 13 C excursions. The latter excursion is paced by obliquity and is therein similar to Mesozoic intervals of environmental upheaval, like the Cretaceous Ocean-Anoxic-Event-2 (OAE-2). This obliquity signature implies coincidence with a minimum of the 2.4 Myr eccentricity cycle, during which obliquity prevails over precession, and highlights the decisive role of astronomically forced "Milankovitch" climate change in timing and pacing the Late Devonian mass extinction.

  2. Dynamics of origination and extinction in the marine fossil record

    PubMed Central

    Alroy, John

    2008-01-01

    The discipline-wide effort to database the fossil record at the occurrence level has made it possible to estimate marine invertebrate extinction and origination rates with much greater accuracy. The new data show that two biotic mechanisms have hastened recoveries from mass extinctions and confined diversity to a relatively narrow range over the past 500 million years (Myr). First, a drop in diversity of any size correlates with low extinction rates immediately afterward, so much so that extinction would almost come to a halt if diversity dropped by 90%. Second, very high extinction rates are followed by equally high origination rates. The two relationships predict that the rebound from the current mass extinction will take at least 10 Myr, and perhaps 40 Myr if it rivals the Permo-Triassic catastrophe. Regardless, any large event will result in a dramatic ecological and taxonomic restructuring of the biosphere. The data also confirm that extinction and origination rates both declined through the Phanerozoic and that several extinctions in addition to the Permo-Triassic event were particularly severe. However, the trend may be driven by taxonomic biases and the rates vary in accord with a simple log normal distribution, so there is no sharp distinction between background and mass extinctions. Furthermore, the lack of any significant autocorrelation in the data is inconsistent with macroevolutionary theories of periodicity or self-organized criticality. PMID:18695240

  3. Contrasting microbial community changes during mass extinctions at the Middle/Late Permian and Permian/Triassic boundaries

    NASA Astrophysics Data System (ADS)

    Xie, Shucheng; Algeo, Thomas J.; Zhou, Wenfeng; Ruan, Xiaoyan; Luo, Genming; Huang, Junhua; Yan, Jiaxin

    2017-02-01

    Microbial communities are known to expand as a result of environmental deterioration during mass extinctions, but differences in microbial community changes between extinction events and their underlying causes have received little study to date. Here, we present a systematic investigation of microbial lipid biomarkers spanning ∼20 Myr (Middle Permian to Early Triassic) at Shangsi, South China, to contrast microbial changes associated with the Guadalupian-Lopingian boundary (GLB) and Permian-Triassic boundary (PTB) mass extinctions. High-resolution analysis of the PTB crisis interval reveals a distinct succession of microbial communities based on secular variation in moretanes, 2-methylhopanes, aryl isoprenoids, steranes, n-alkyl cyclohexanes, and other biomarkers. The first episode of the PTB mass extinction (ME1) was associated with increases in red algae and nitrogen-fixing bacteria along with evidence for enhanced wildfires and elevated soil erosion, whereas the second episode was associated with expansions of green sulfur bacteria, nitrogen-fixing bacteria, and acritarchs coinciding with climatic hyperwarming, ocean stratification, and seawater acidification. This pattern of microbial community change suggests that marine environmental deterioration was greater during the second extinction episode (ME2). The GLB shows more limited changes in microbial community composition and more limited environmental deterioration than the PTB, consistent with differences in species-level extinction rates (∼71% vs. 90%, respectively). Microbial biomarker records have the potential to refine our understanding of the nature of these crises and to provide insights concerning possible outcomes of present-day anthropogenic stresses on Earth's ecosystems.

  4. Influence of Feeding and Body Mass on IUCN Extinction Threat of Extant Marine and Terrestrial Mammals

    NASA Astrophysics Data System (ADS)

    Lam, G.; Wang, I. M.; Heim, N.; Payne, J.

    2016-12-01

    Extinction is a fundamental phenomenon that has been occurring for millions of years and is critical to the development of new organisms and niches. However, the current extinction rate is now one hundred to a thousand times the past background extinction rate due to human influences and rapidly changing environments. Research on geographic range and life history has been performed in extinction analyses, but rarely any on feeding type and trophic level. We compiled data from the IUCN Red List Database, Paleobiology database and diets from Pauly et al. (1998) to explore the possible correlation between various aspects of ecology and extinction threat. By doing so, we can better understand where to focus our conservation efforts, and what type of approach will reap the best results. We discovered that terrestrial carnivores are slightly less at risk than herbivores and omnivores, and that the feeding and tiering of marine mammals have minimal effect on their IUCN threat level. Body mass is the most influential factor on risk level, with larger adult body masses being most at risk.

  5. The tree balance signature of mass extinction is erased by continued evolution in clades of constrained size with trait-dependent speciation

    PubMed Central

    Yang, Guan-Dong; Agapow, Paul-Michael

    2017-01-01

    The kind and duration of phylogenetic topological “signatures” left in the wake of macroevolutionary events remain poorly understood. To this end, we examined a broad range of simulated phylogenies generated using trait-biased, heritable speciation probabilities and mass extinction that could be either random or selective on trait value, but also using background extinction and diversity-dependence to constrain clade sizes. In keeping with prior results, random mass extinction increased imbalance of clades that recovered to pre-extinction size, but was a relatively weak effect. Mass extinction that was selective on trait values tended to produce clades of similar or greater balance compared to random extinction or controls. Allowing evolution to continue past the point of clade-size recovery resulted in erosion and eventual erasure of this signal, with all treatments converging on similar values of imbalance, except for very intense extinction regimes targeted at taxa with high speciation rates. Return to a more balanced state with extended post-extinction evolution was also associated with loss of the previous phylogenetic root in most treatments. These results further demonstrate that while a mass extinction event can produce a recognizable phylogenetic signal, its effects become increasingly obscured the further an evolving clade gets from that event, with any sharp imbalance due to unrelated evolutionary factors. PMID:28644846

  6. Pre- versus post-mass extinction divergence of Mesozoic marine reptiles dictated by time-scale dependence of evolutionary rates.

    PubMed

    Motani, Ryosuke; Jiang, Da-Yong; Tintori, Andrea; Ji, Cheng; Huang, Jian-Dong

    2017-05-17

    The fossil record of a major clade often starts after a mass extinction even though evolutionary rates, molecular or morphological, suggest its pre-extinction emergence (e.g. squamates, placentals and teleosts). The discrepancy is larger for older clades, and the presence of a time-scale-dependent methodological bias has been suggested, yet it has been difficult to avoid the bias using Bayesian phylogenetic methods. This paradox raises the question of whether ecological vacancies, such as those after mass extinctions, prompt the radiations. We addressed this problem by using a unique temporal characteristic of the morphological data and a high-resolution stratigraphic record, for the oldest clade of Mesozoic marine reptiles, Ichthyosauromorpha. The evolutionary rate was fastest during the first few million years of ichthyosauromorph evolution and became progressively slower over time, eventually becoming six times slower. Using the later slower rates, estimates of divergence time become excessively older. The fast, initial rate suggests the emergence of ichthyosauromorphs after the end-Permian mass extinction, matching an independent result from high-resolution stratigraphic confidence intervals. These reptiles probably invaded the sea as a new ecosystem was formed after the end-Permian mass extinction. Lack of information on early evolution biased Bayesian clock rates. © 2017 The Author(s).

  7. Pre- versus post-mass extinction divergence of Mesozoic marine reptiles dictated by time-scale dependence of evolutionary rates

    PubMed Central

    Ji, Cheng; Huang, Jian-dong

    2017-01-01

    The fossil record of a major clade often starts after a mass extinction even though evolutionary rates, molecular or morphological, suggest its pre-extinction emergence (e.g. squamates, placentals and teleosts). The discrepancy is larger for older clades, and the presence of a time-scale-dependent methodological bias has been suggested, yet it has been difficult to avoid the bias using Bayesian phylogenetic methods. This paradox raises the question of whether ecological vacancies, such as those after mass extinctions, prompt the radiations. We addressed this problem by using a unique temporal characteristic of the morphological data and a high-resolution stratigraphic record, for the oldest clade of Mesozoic marine reptiles, Ichthyosauromorpha. The evolutionary rate was fastest during the first few million years of ichthyosauromorph evolution and became progressively slower over time, eventually becoming six times slower. Using the later slower rates, estimates of divergence time become excessively older. The fast, initial rate suggests the emergence of ichthyosauromorphs after the end-Permian mass extinction, matching an independent result from high-resolution stratigraphic confidence intervals. These reptiles probably invaded the sea as a new ecosystem was formed after the end-Permian mass extinction. Lack of information on early evolution biased Bayesian clock rates. PMID:28515201

  8. Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction

    NASA Astrophysics Data System (ADS)

    Ruhl, Micha; Bonis, Nina R.; Reichart, Gert-Jan; Damsté, Jaap S. Sinninghe; Kürschner, Wolfram M.

    2011-07-01

    The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 103 gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change.

  9. Atmospheric carbon injection linked to end-Triassic mass extinction.

    PubMed

    Ruhl, Micha; Bonis, Nina R; Reichart, Gert-Jan; Sinninghe Damsté, Jaap S; Kürschner, Wolfram M

    2011-07-22

    The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 10(3) gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change.

  10. Extinction from a paleontological perspective

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1993-01-01

    Extinction of widespread species is common in evolutionary time (millions of years) but rare in ecological time (hundreds or thousands of years). In the fossil record, there appears to be a smooth continuum between background and mass extinction; and the clustering of extinctions at mass extinctions cannot be explained by the chance coincidence of independent events. Although some extinction is selective, much is apparently random in that survivors have no recognizable superiority over victims. Extinction certainly plays an important role in evolution, but whether it is constructive or destructive has not yet been determined.

  11. Strangelove Ocean and Deposition of Unusual Shallow-Water Carbonates After the End-Permian Mass Extinction

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Caldeira, Ken

    2003-01-01

    The severe mass extinction of marine and terrestrial organisms at the end of the Permian Period (approx. 251 Ma) was accompanied by a rapid negative excursion of approx. 3 to 4 per mil in the carbon-isotope ratio of the global surface oceans and atmosphere that persisted for some 500,000 into the Early Triassic. Simulations with an ocean-atmosphere/carbon-cycle model suggest that the isotope excursion can be explained by collapse of ocean primary productivity (a Strangelove Ocean) and changes in the delivery and cycling of carbon in the ocean and on land. Model results also suggest that perturbations of the global carbon cycle resulting from the extinctions led to short-term fluctuations in atmospheric pCO2 and ocean carbonate deposition, and to a long-term (>1 Ma) decrease in sedimentary burial of organic carbon in the Triassic. Deposition of calcium carbonate is a major sink of river-derived ocean alkalinity and for CO2 from the ocean/atmosphere system. The end of the Permian was marked by extinction of most calcium carbonate secreting organisms. Therefore, the reduction of carbonate accumulation made the oceans vulnerable to a build-up of alkalinity and related fluctuations in atmospheric CO2. Our model results suggest that an increase in ocean carbonate-ion concentration should cause increased carbonate accumulation rates in shallow-water settings. After the end-Permian extinctions, early Triassic shallow-water sediments show an abundance of abiogenic and microbial carbonates that removed CaCO3 from the ocean and may have prevented a full 'ocean-alkalinity crisis' from developing.

  12. Science observed: The mass-extinction debates

    NASA Technical Reports Server (NTRS)

    Glen, W.

    1994-01-01

    The upheaval triggered in 1980 by the Alvarez-Berkeley group impact hypothesis transformed the literature of mass extinctions from an unfocused, sporadic collection of papers that virtually ignored extraterrestrial causes and treated endogenous ones only sparingly better to an integrated, diverse body of literature. Research programs organized seemingly overnight spawned collaborative teams whose members, often from distant, isolated disciplines, redirected their careers in order to address the captivating, high-stakes issues. The initial, generally skeptical, cool reception of the impact hypothesis might have been predicted for any of a number of reasons: such an instantaneous catastrophe contravened earth science's reigning philosophy of uniformitarianism; it was formulated from a form of evidence - siderophile element anomalies - alien to the community charged with its appraisal; it advanced a causal mechanism that was improbable in terms of canonical knowledge; and it was proffered mainly by specialists alien to earth and biological science, especially paleobiology. Early on it became clear that irrespective of which causal hypothesis was chosen, the chosen one would be the strongest predictor of how the chooser would select and apply standards in assessing evidence bearing on all such hypothesis. Less strong correlation also appeared between disciplinary speciality and the assessment of evidence. Such correlations varied with the level of specialization; the most robust correlations appeared in the broadest areas of science practice. The gestalt (mindset) seemingly engendered by the embrace of an extinction hypothesis overrode, or was stronger than, the intellectual predispositions attributable to disciplinary specialty.

  13. Science observed: The mass-extinction debates

    NASA Astrophysics Data System (ADS)

    Glen, W.

    The upheaval triggered in 1980 by the Alvarez-Berkeley group impact hypothesis transformed the literature of mass extinctions from an unfocused, sporadic collection of papers that virtually ignored extraterrestrial causes and treated endogenous ones only sparingly better to an integrated, diverse body of literature. Research programs organized seemingly overnight spawned collaborative teams whose members, often from distant, isolated disciplines, redirected their careers in order to address the captivating, high-stakes issues. The initial, generally skeptical, cool reception of the impact hypothesis might have been predicted for any of a number of reasons: such an instantaneous catastrophe contravened earth science's reigning philosophy of uniformitarianism; it was formulated from a form of evidence - siderophile element anomalies - alien to the community charged with its appraisal; it advanced a causal mechanism that was improbable in terms of canonical knowledge; and it was proffered mainly by specialists alien to earth and biological science, especially paleobiology. Early on it became clear that irrespective of which causal hypothesis was chosen, the chosen one would be the strongest predictor of how the chooser would select and apply standards in assessing evidence bearing on all such hypothesis. Less strong correlation also appeared between disciplinary speciality and the assessment of evidence. Such correlations varied with the level of specialization; the most robust correlations appeared in the broadest areas of science practice. The gestalt (mindset) seemingly engendered by the embrace of an extinction hypothesis overrode, or was stronger than, the intellectual predispositions attributable to disciplinary specialty.

  14. Comparative Earth history and Late Permian mass extinction

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Bambach, R. K.; Canfield, D. E.; Grotzinger, J. P.

    1996-01-01

    The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

  15. A scale of greatness and causal classification of mass extinctions: Implications for mechanisms

    PubMed Central

    Şengör, A. M. Celâl; Atayman, Saniye; Özeren, Sinan

    2008-01-01

    A quantitative scale for measuring greatness, G, of mass extinctions is proposed on the basis of rate of biodiversity diminution expressed as the product of the loss of biodiversity, called magnitude (M), and the inverse of time in which that loss occurs, designated as intensity (I). On this scale, the catastrophic Cretaceous–Tertiary (K-T) extinction appears as the greatest since the Ordovician and the only one with a probable extraterrestrial cause. The end-Permian extinction was less great but with a large magnitude (M) and smaller intensity (I); only some of its individual episodes involved some semblance of catastrophe. Other extinctions during the Phanerozoic, with the possible exception of the end-Silurian diversity plunge, were parts of a forced oscillatory phenomenon and seem caused by marine- and land-habitat destruction during continental assemblies that led to elimination of shelves and (after the Devonian) rain forests and enlargement of deserts. Glaciations and orogenies that shortened and thickened the continental crust only exacerbated these effects. During the Mesozoic and Cainozoic, the evolution of life was linearly progressive, interrupted catastrophically only at the K-T boundary. The end-Triassic extinction was more like the Paleozoic extinctions in nature and probably also in its cause. By contrast, the current extinction resembles none of the earlier ones and may end up being the greatest of all. PMID:18779562

  16. Environmental conditions as the cause of the great mass extinction of marine organisms in the Late Devonian

    NASA Astrophysics Data System (ADS)

    Barash, M. S.

    2017-08-01

    During the Late Devonian extinction, 70-82% of all marine species disappeared. The main causes of this mass extinction include tectonic activity, climate and sea-level fluctuations, volcanism, and the collision of the Earth with cosmic bodies (impact events). The major causes are considered to be volcanism accompanying formation of the Viluy traps and, probably, basaltic magmatism in the Southern Urals, alkaline magmatism within the East European platform, and volcanism in northern Iran and northern and southern China. Several large impact craters of Late Devonian age have been documented in different parts of the world. The available data indicate that this time period on the Earth was marked by two major sequences of events: terrestrial events that resulted in extensive volcanism and cosmic (or impact) events. They produced similar effects such as emissions of harmful chemical compounds and aerosols to cause greenhouse warming and the darkening of the atmosphere, which prevented photosynthesis and cause ocean stagnation and anoxia. This disrupted the food chain and reduced ecosystem productivity. As a result, all vital processes were disturbed and a large part of the marine biota became extinct.

  17. Lognormals for SETI, Evolution and Mass Extinctions

    NASA Astrophysics Data System (ADS)

    Maccone, Claudio

    2014-12-01

    In a series of recent papers (Refs. [1-5,7,8]) and in a book (Ref. [6]), this author suggested a new mathematical theory capable of merging Darwinian Evolution and SETI into a unified statistical framework. In this new vision, Darwinian Evolution, as it unfolded on Earth over the last 3.5 billion years, is defined as just one particular realization of a certain lognormal stochastic process in the number of living species on Earth, whose mean value increased in time exponentially. SETI also may be brought into this vision since the number of communicating civilizations in the Galaxy is given by a lognormal distribution (Statistical Drake Equation). Now, in this paper we further elaborate on all that particularly with regard to two important topics: The introduction of the general lognormal stochastic process L(t) whose mean value may be an arbitrary continuous function of the time, m(t), rather than just the exponential mGBM (t) =N0eμt typical of the Geometric Brownian Motion (GBM). This is a considerable generalization of the GBM-based theory used in Refs. [1-8]. The particular application of the general stochastic process L(t) to the understanding of Mass Extinctions like the K-Pg one that marked the dinosaurs' end 65 million years ago. We first model this Mass Extinction as a decreasing Geometric Brownian Motion (GBM) extending from the asteroid's impact time all through the ensuing 'nuclear winter'. However, this model has a flaw: the 'final value' of the GBM cannot have a horizontal tangent, as requested to enable the recovery of life again after this 'final extinction value'. That flaw, however, is removed if the rapidly decreasing mean value function of L(t) is the left branch of a parabola extending from the asteroid's impact time all through the ensuing 'nuclear winter' and up to the time when the number of living species on Earth started growing up again, as we show mathematically in Section 3. In conclusion, we have uncovered an important generalization

  18. Could a nearby supernova explosion have caused a mass extinction?

    PubMed

    Ellis, J; Schramm, D N

    1995-01-03

    We examine the possibility that a nearby supernova explosion could have caused one or more of the mass extinctions identified by paleontologists. We discuss the possible rate of such events in the light of the recent suggested identification of Geminga as a supernova remnant less than 100 parsec (pc) away and the discovery of a millisecond pulsar about 150 pc away and observations of SN 1987A. The fluxes of gamma-radiation and charged cosmic rays on the Earth are estimated, and their effects on the Earth's ozone layer are discussed. A supernova explosion of the order of 10 pc away could be expected as often as every few hundred million years and could destroy the ozone layer for hundreds of years, letting in potentially lethal solar ultraviolet radiation. In addition to effects on land ecology, this could entail mass destruction of plankton and reef communities, with disastrous consequences for marine life as well. A supernova extinction should be distinguishable from a meteorite impact such as the one that presumably killed the dinosaurs at the "KT boundary." The recent argument that the KT event was exceedingly large and thus quite rare supports the need for other catastrophic events.

  19. The Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function

    NASA Astrophysics Data System (ADS)

    Habibi, M.; Stolte, A.; Brandner, W.; Hußmann, B.; Motohara, K.

    2013-08-01

    The Galactic center is the most active site of star formation in the Milky Way, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic center through the Galactic disk, knowledge of extinction is crucial when studying this region. The Arches cluster is a young, massive starburst cluster near the Galactic center. We observed the Arches cluster out to its tidal radius using Ks-band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/CISCO J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and ΔAKs ~ 1 magnitude in acquired Ks-band extinction, while the present-day mass function slope changes by ~ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law increases from a flat slope of αNishi = -1.50 ± 0.35 in the core (r < 0.2 pc) to αNishi = -2.21 ± 0.27 in the intermediate annulus (0.2 < r < 0.4 pc), where the Salpeter slope is -2.3. The mass function steepens to αNishi = -3.21 ± 0.30 in the outer annulus (0.4 < r < 1.5 pc), indicating that the outer cluster region is depleted of high-mass stars. This picture is consistent with mass segregation owing to the dynamical evolution of the cluster. Based on observations collected at the ESO/VLT under Program ID 081.D-0572(B) (PI: Brandner) and ID 71.C-0344(A) (PI: Eisenhauer, retrieved from the ESO archive). Also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.Full Table 5 is

  20. Body Size Preference of Marine Animals in Relation to Extinction Selectivity

    NASA Astrophysics Data System (ADS)

    Sriram, A.; Idgunji, S.; Heim, N. A.; Payne, J.

    2014-12-01

    Our project encompasses an extremely specific aspect in relation to the five mass extinctions in geologic history. We asked ourselves whether larger or smaller body sizes would be better suited for surviving a mass extinction. To conduct research for our project, we used the body sizes of 17,172 marine animal genera as our primary data. These animals include echinoderms, arthropods, chordates, mollusks, and brachiopods. These creatures are perfect model organisms in terms of finding data on them because they have an excellent fossil record, and are well documented. We focused on the mean body size of these animals before and after each of the five mass extinctions (end-Ordovician, Late Devonian, end-Permian, end-Triassic, and end-Cretaceous). Our hypothesis was that the average biovolume of animals increased after each of the extinctions, with the mean size being greater after than it was before. Our size data is from the Ellis & Messina Catalogue of Ostracoda and the Treatise on Invertebrate Paleontology. We obtained stratigraphic range data The Treatise and Sepkoski (2002). In our analyses, we compared the mean size of the different animal genera before and after each extinction event. We further partitioned size change across mass extinction boundaries into three categories: the surviving genera, the extinct genera, and the newly originating genera that came about after the extinction. According to our analyses, the mean sizes did not change significantly from the genera living during the stages before the extinctions and after the extinctions. From our results, we can assume that there were not enough major increases in the overall volume of the organisms to warrant a definite conclusion that extinctions lead to larger body sizes. Further support for our findings came from the T-tests in our R code. Only the Cretaceous period showed true evidence for size changing because of the extinction; in this case, the mean size decreased. T-tests for the Cretaceous

  1. Earth history. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction.

    PubMed

    Schoene, Blair; Samperton, Kyle M; Eddy, Michael P; Keller, Gerta; Adatte, Thierry; Bowring, Samuel A; Khadri, Syed F R; Gertsch, Brian

    2015-01-09

    The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply uranium-lead (U-Pb) zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million cubic kilometers of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions. Copyright © 2015, American Association for the Advancement of Science.

  2. Mercury evidence for pulsed volcanism during the end-Triassic mass extinction

    PubMed Central

    Percival, Lawrence M. E.; Ruhl, Micha; Hesselbo, Stephen P.; Jenkyns, Hugh C.; Mather, Tamsin A.; Whiteside, Jessica H.

    2017-01-01

    The Central Atlantic Magmatic Province (CAMP) has long been proposed as having a causal relationship with the end-Triassic extinction event (∼201.5 Ma). In North America and northern Africa, CAMP is preserved as multiple basaltic units interbedded with uppermost Triassic to lowermost Jurassic sediments. However, it has been unclear whether this apparent pulsing was a local feature, or if pulses in the intensity of CAMP volcanism characterized the emplacement of the province as a whole. Here, six geographically widespread Triassic–Jurassic records, representing varied paleoenvironments, are analyzed for mercury (Hg) concentrations and Hg/total organic carbon (Hg/TOC) ratios. Volcanism is a major source of mercury to the modern environment. Clear increases in Hg and Hg/TOC are observed at the end-Triassic extinction horizon, confirming that a volcanically induced global Hg cycle perturbation occurred at that time. The established correlation between the extinction horizon and lowest CAMP basalts allows this sedimentary Hg excursion to be stratigraphically tied to a specific flood basalt unit, strengthening the case for volcanic Hg as the driver of sedimentary Hg/TOC spikes. Additional Hg/TOC peaks are also documented between the extinction horizon and the Triassic–Jurassic boundary (separated by ∼200 ky), supporting pulsatory intensity of CAMP volcanism across the entire province and providing direct evidence for episodic volatile release during the initial stages of CAMP emplacement. Pulsatory volcanism, and associated perturbations in the ocean–atmosphere system, likely had profound implications for the rate and magnitude of the end-Triassic mass extinction and subsequent biotic recovery. PMID:28630294

  3. Mercury evidence for pulsed volcanism during the end-Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Percival, Lawrence M. E.; Ruhl, Micha; Hesselbo, Stephen P.; Jenkyns, Hugh C.; Mather, Tamsin A.; Whiteside, Jessica H.

    2017-07-01

    The Central Atlantic Magmatic Province (CAMP) has long been proposed as having a causal relationship with the end-Triassic extinction event (˜201.5 Ma). In North America and northern Africa, CAMP is preserved as multiple basaltic units interbedded with uppermost Triassic to lowermost Jurassic sediments. However, it has been unclear whether this apparent pulsing was a local feature, or if pulses in the intensity of CAMP volcanism characterized the emplacement of the province as a whole. Here, six geographically widespread Triassic-Jurassic records, representing varied paleoenvironments, are analyzed for mercury (Hg) concentrations and Hg/total organic carbon (Hg/TOC) ratios. Volcanism is a major source of mercury to the modern environment. Clear increases in Hg and Hg/TOC are observed at the end-Triassic extinction horizon, confirming that a volcanically induced global Hg cycle perturbation occurred at that time. The established correlation between the extinction horizon and lowest CAMP basalts allows this sedimentary Hg excursion to be stratigraphically tied to a specific flood basalt unit, strengthening the case for volcanic Hg as the driver of sedimentary Hg/TOC spikes. Additional Hg/TOC peaks are also documented between the extinction horizon and the Triassic-Jurassic boundary (separated by ˜200 ky), supporting pulsatory intensity of CAMP volcanism across the entire province and providing direct evidence for episodic volatile release during the initial stages of CAMP emplacement. Pulsatory volcanism, and associated perturbations in the ocean-atmosphere system, likely had profound implications for the rate and magnitude of the end-Triassic mass extinction and subsequent biotic recovery.

  4. Redox chemistry changes in the Panthalassic Ocean linked to the end-Permian mass extinction and delayed Early Triassic biotic recovery

    NASA Astrophysics Data System (ADS)

    Zhang, Guijie; Zhang, Xiaolin; Hu, Dongping; Li, Dandan; Algeo, Thomas J.; Farquhar, James; Henderson, Charles M.; Qin, Liping; Shen, Megan; Shen, Danielle; Schoepfer, Shane D.; Chen, Kefan; Shen, Yanan

    2017-02-01

    The end-Permian mass extinction represents the most severe biotic crisis for the last 540 million years, and the marine ecosystem recovery from this extinction was protracted, spanning the entirety of the Early Triassic and possibly longer. Numerous studies from the low-latitude Paleotethys and high-latitude Boreal oceans have examined the possible link between ocean chemistry changes and the end-Permian mass extinction. However, redox chemistry changes in the Panthalassic Ocean, comprising ˜85-90% of the global ocean area, remain under debate. Here, we report multiple S-isotopic data of pyrite from Upper Permian-Lower Triassic deep-sea sediments of the Panthalassic Ocean, now present in outcrops of western Canada and Japan. We find a sulfur isotope signal of negative Δ33S with either positive δ34S or negative δ34S that implies mixing of sulfide sulfur with different δ34S before, during, and after the end-Permian mass extinction. The precise coincidence of the negative Δ33S anomaly with the extinction horizon in western Canada suggests that shoaling of H2S-rich waters may have driven the end-Permian mass extinction. Our data also imply episodic euxinia and oscillations between sulfidic and oxic conditions during the earliest Triassic, providing evidence of a causal link between incursion of sulfidic waters and the delayed recovery of the marine ecosystem.

  5. 2MASS wide-field extinction maps. V. Corona Australis

    NASA Astrophysics Data System (ADS)

    Alves, João; Lombardi, Marco; Lada, Charles J.

    2014-05-01

    We present a near-infrared extinction map of a large region (~870 deg2) covering the isolated Corona Australis complex of molecular clouds. We reach a 1-σ error of 0.02 mag in the K-band extinction with a resolution of 3 arcmin over the entire map. We find that the Corona Australis cloud is about three times as large as revealed by previous CO and dust emission surveys. The cloud consists of a 45 pc long complex of filamentary structure from the well known star forming Western-end (the head, N ≥ 1023 cm-2) to the diffuse Eastern-end (the tail, N ≤ 1021 cm-2). Remarkably, about two thirds of the complex both in size and mass lie beneath AV ~ 1 mag. We find that the probability density function (PDF) of the cloud cannot be described by a single log-normal function. Similar to prior studies, we found a significant excess at high column densities, but a log-normal + power-law tail fit does not work well at low column densities. We show that at low column densities near the peak of the observed PDF, both the amplitude and shape of the PDF are dominated by noise in the extinction measurements making it impractical to derive the intrinsic cloud PDF below AK < 0.15 mag. Above AK ~ 0.15 mag, essentially the molecular component of the cloud, the PDF appears to be best described by a power-law with index -3, but could also described as the tail of a broad and relatively low amplitude, log-normal PDF that peaks at very low column densities. FITS files of the extinction maps are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/565/A18

  6. Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle

    PubMed Central

    Irmis, Randall B.; Whiteside, Jessica H.

    2012-01-01

    During the end-Permian mass extinction, marine ecosystems suffered a major drop in diversity, which was maintained throughout the Early Triassic until delayed recovery during the Middle Triassic. This depressed diversity in the Early Triassic correlates with multiple major perturbations to the global carbon cycle, interpreted as either intrinsic ecosystem or external palaeoenvironmental effects. In contrast, the terrestrial record of extinction and recovery is less clear; the effects and magnitude of the end-Permian extinction on non-marine vertebrates are particularly controversial. We use specimen-level data from southern Africa and Russia to investigate the palaeodiversity dynamics of non-marine tetrapods across the Permo-Triassic boundary by analysing sample-standardized generic richness, evenness and relative abundance. In addition, we investigate the potential effects of sampling, geological and taxonomic biases on these data. Our analyses demonstrate that non-marine tetrapods were severely affected by the end-Permian mass extinction, and that these assemblages did not begin to recover until the Middle Triassic. These data are congruent with those from land plants and marine invertebrates. Furthermore, they are consistent with the idea that unstable low-diversity post-extinction ecosystems were subject to boom–bust cycles, reflected in multiple Early Triassic perturbations of the carbon cycle. PMID:22031757

  7. Evolution and extinction in the marine realm: some constraints imposed by phytoplankton

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.

    1989-01-01

    The organic and mineralized remains of planktonic algae provide a rich record of microplankton evolution extending over nearly half of the preserved geological record. In general, Phanerozoic patterns of phytoplankton radiation and extinction parallel those documented for skeletonized marine invertebrates, both augmenting and constraining thought about evolution in the oceans. Rapidly increasing knowledge of Proterozoic plankton is making possible the recognition of additional episodes of diversification and extinction that antedate the Ediacaran radiation of macroscopic animals. In contrast to earlier phytoplankton history, the late Mesozoic and Cainozoic record is documented in sufficient detail to constrain theories of mass extinction in more than a general way. Broad patterns of diversity change in planktonic algae show similarities across the Cretaceous-Tertiary and Eocene-Oligocene boundaries, but detailed comparisons of origination and extinction rates in calcareous nannoplankton, as well as other algae and skeletonized protozoans, suggest that the two episodes were quite distinct. Common causation appears unlikely, casting doubt on monolithic theories of mass extinction, whether periodic or not. Studies of mass extinction highlight a broader class of insights that paleontologists can contribute to evolutionary biology: the evaluation of evolutionary change in the context of evolving Earth-surface environments.

  8. Could a nearby supernova explosion have caused a mass extinction?

    SciTech Connect

    Ellis, J.; Schramm, D.N.

    1995-01-03

    We examine the possibility that a nearby supernova explosion could have caused one or more of the mass extinctions identified by paleontologists. We discuss the possible rate of such events in the light of the recent suggested identification of Geminga as a supernova remnant less than 100 parsec (pc) away and the discovery of a millisecond pulsar about 150 pc away and observations of SN 1987A. The fluxes of {gamma}-radiation and charged cosmic rays on the Earth are estimated, and their effects on the Earth`s ozone layer are discussed. A supernova explosion of the order of 10 pc away couldmore » be expected as often as every few hundred million years and could destroy the ozone layer for hundreds of years, letting in potentially lethal solar ultraviolet radiation. In addition to effects on land ecology, this could entail mass destruction of plankton and reef communities, with disastrous consequences for marine life as well. A supernova extinction should be distinguishable from a meteorite impact such as the one that presumably killed the dinosaurs at the {open_quotes}KT boundary.{close_quotes} The recent argument that the KT event was exceedingly large and thus quite rare supports the need for other catastrophic events. 24 refs.« less

  9. Could a nearby supernova explosion have caused a mass extinction?

    PubMed Central

    Ellis, J; Schramm, D N

    1995-01-01

    We examine the possibility that a nearby supernova explosion could have caused one or more of the mass extinctions identified by paleontologists. We discuss the possible rate of such events in the light of the recent suggested identification of Geminga as a supernova remnant less than 100 parsec (pc) away and the discovery of a millisecond pulsar about 150 pc away and observations of SN 1987A. The fluxes of gamma-radiation and charged cosmic rays on the Earth are estimated, and their effects on the Earth's ozone layer are discussed. A supernova explosion of the order of 10 pc away could be expected as often as every few hundred million years and could destroy the ozone layer for hundreds of years, letting in potentially lethal solar ultraviolet radiation. In addition to effects on land ecology, this could entail mass destruction of plankton and reef communities, with disastrous consequences for marine life as well. A supernova extinction should be distinguishable from a meteorite impact such as the one that presumably killed the dinosaurs at the "KT boundary." The recent argument that the KT event was exceedingly large and thus quite rare supports the need for other catastrophic events. PMID:11607506

  10. The Permian-Triassic boundary & mass extinction in China

    USGS Publications Warehouse

    Metcalfe, I.; Nicoll, R.S.; Mundil, R.; Foster, C.; Glen, J.; Lyons, J.; Xiaofeng, W.; Cheng-Yuan, W.; Renne, P.R.; Black, L.; Xun, Q.; Xiaodong, M.

    2001-01-01

    The first appearance of Hindeodus parvus (Kozur & Pjatakova) at the Permian-Triassic (P-T) GSSP level (base of Bed 27c) at Meishan is here confirmed. Hindeodus changxingensis Wang occurs from Beds 26 to 29 at Meishan and appears to be restricted to the narrow boundary interval immediately above the main mass extinction level in Bed 25. It is suggested that this species is therefore a valuable P-T boundary interval index taxon. Our collections from the Shangsi section confirm that the first occurrence of Hindeodus parvus in that section is about 5 in above the highest level from which a typical Permian fauna is recovered. This may suggest that that some section may be missing at Meishan. The age of the currently defined Permian-Triassic Boundary is estimated by our own studies and a reassessment of previous worker's data at c. 253 Ma, slightly older than our IDTIMS 206Pb/238U age of 252.5 ??0.3 Ma for Bed 28, just 8 cm above the GSSP boundary (Mundil et al., 2001). The age of the main mass extinction, at the base of Bed 25 at Meishan, is estimated at slightly older than 254 Ma based on an age of >254 Ma for the Bed 25 ash. Regardless of the absolute age of the boundary, it is evident that the claimed <165,000 y short duration for the negative carbon isotope excursion at the P-T boundary (Bowring et al., 1998) cannot be confirmed. Purportedly extraterrestrial fullerenes at the boundary (Hecker et al., 2001) have equivocal significance due to their chronostratigraphic non-uniqueness and their occurrence in a volcanic ash.

  11. Periodic cometary showers: Real or imaginary?

    NASA Technical Reports Server (NTRS)

    Grieve, R. A. F.; Sharpton, V. L.; Goodacre, A. K.; Garvin, J. B.

    1985-01-01

    Since the initial reports in 1980, a considerable body of chemical and physical evidence has been accumulated to indicate that a major impact event occurred on earth 65 million years ago. The effects of this event were global in extent and have been suggested as the cause of the sudden demise or mass extinction of a large percentage of life, including the dinosaurs, at the end of the geologic time period known as the Cretaceous. Recent statistical analyses of extinctions in the marine faunal record for the last 250 million years have suggested that mass extinctions may occur with a periodicity of every 26 to 30 million years. Following these results, other workers have attempted to demonstrate that these extinction events, like that at the end of the Cretaceous, are temporally correlated with large impact events. A recent scenario suggests that they are the result of periodic showers of comets produced by either the passage of the solar system through the galactic plane or by perturbations of the cometary cloud in the outer solar system by a, as yet unseen, solar companion. This hypothesized solar companion has been given the name Nemesis.

  12. The visible extinction peaks of Ag nanohelixes: A periodic effective dipole model

    SciTech Connect

    Zhang, Z.-Y.; Zhao, Y.-P.

    2011-02-21

    Using the discrete dipole approximation method, two visible extinction peaks are found for Ag nanohelixes. Both of them redshift periodically in an approximate half pitch with the helix height and redshift linearly with the helix diameter and pitch height. At the two absorbance peaks, an integer number of E-field maxima occur along the helix. These field maxima could be treated as results of collective electron oscillations by periodic effective dipoles within a half pitch along the helix. The wavelengths of the absorbance peaks are found to scale with the effective dipole length, which is consistent with the periodic structure ofmore » the helix.« less

  13. Unusual Deep Water sponge assemblage in South China—Witness of the end-Ordovician mass extinction

    NASA Astrophysics Data System (ADS)

    Li, Lixia; Feng, Hongzhen; Janussen, Dorte; Reitner, Joachim

    2015-11-01

    There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China.

  14. Unusual Deep Water sponge assemblage in South China—Witness of the end-Ordovician mass extinction

    PubMed Central

    Li, Lixia; Feng, Hongzhen; Janussen, Dorte; Reitner, Joachim

    2015-01-01

    There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China. PMID:26538179

  15. Unusual Deep Water sponge assemblage in South China-Witness of the end-Ordovician mass extinction.

    PubMed

    Li, Lixia; Feng, Hongzhen; Janussen, Dorte; Reitner, Joachim

    2015-11-05

    There are few sponges known from the end-Ordovician to early-Silurian strata all over the world, and no records of sponge fossils have been found yet in China during this interval. Here we report a unique sponge assemblage spanning the interval of the end-Ordovician mass extinction from the Kaochiapien Formation (Upper Ordovician-Lower Silurian) in South China. This assemblage contains a variety of well-preserved siliceous sponges, including both Burgess Shale-type and modern type taxa. It is clear that this assemblage developed in deep water, low energy ecosystem with less competitors and more vacant niches. Its explosion may be related to the euxinic and anoxic condition as well as the noticeable transgression during the end-Ordovician mass extinction. The excellent preservation of this assemblage is probably due to the rapid burial by mud turbidites. This unusual sponge assemblage provides a link between the Burgess Shale-type deep water sponges and the modern forms. It gives an excellent insight into the deep sea palaeoecology and the macroevolution of Phanerozoic sponges, and opens a new window to investigate the marine ecosystem before and after the end-Ordovician mass extinction. It also offers potential to search for exceptional fossil biota across the Ordovician-Silurian boundary interval in China.

  16. Compound-specific carbon isotopes from Earth’s largest flood basalt eruptions directly linked to the end-Triassic mass extinction

    PubMed Central

    Whiteside, Jessica H.; Olsen, Paul E.; Eglinton, Timothy; Brookfield, Michael E.; Sambrotto, Raymond N.

    2010-01-01

    A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO2. The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie’s Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date. PMID:20308590

  17. Testing the limits in a greenhouse ocean: Did low nitrogen availability limit marine productivity during the end-Triassic mass extinction?

    NASA Astrophysics Data System (ADS)

    Schoepfer, Shane D.; Algeo, Thomas J.; Ward, Peter D.; Williford, Kenneth H.; Haggart, James W.

    2016-10-01

    The end-Triassic mass extinction has been characterized as a 'greenhouse extinction', related to rapid atmospheric warming and associated changes in ocean circulation and oxygenation. The response of the marine nitrogen cycle to these oceanographic changes, and the extent to which mass extinction intervals represent a deviation in nitrogen cycling from other ice-free 'greenhouse' periods of Earth history, remain poorly understood. The well-studied Kennecott Point section in Haida Gwaii, British Columbia, Canada, was deposited in the open Panthalassic Ocean, and is used here as a test case to better understand changes in the nitrogen cycle and marine productivity from the pre-crisis greenhouse of the Rhaetian to the latest-Rhaetian crisis interval. We estimated marine productivity from the late Norian to the early Hettangian using TOC- and P-based paleoproductivity transform equations, and then compared these estimates to records of sedimentary nitrogen isotopes, redox-sensitive trace elements, and biomarker data. Major negative excursions in δ15N (to ≤ 0 ‰) correspond to periods of depressed marine productivity. During these episodes, the development of a stable pycnocline below the base of the photic zone suppressed vertical mixing and limited N availability in surface waters, leading to low productivity and increased nitrogen fixation, as well as ecological stresses in the photic zone. The subsequent shoaling of euxinic waters into the ocean surface layer was fatal for most Triassic marine fauna, although the introduction of regenerated NH4+ into the photic zone may have allowed phytoplankton productivity to recover. These results indicate that the open-ocean nitrogen cycle was influenced by climatic changes during the latest Triassic, despite having existed in a greenhouse state for over 50 million years previously, and that low N availability limited marine productivity for hundreds of thousands of years during the end-Triassic crisis.

  18. Rebuilding Biodiversity of Patagonian Marine Molluscs after the End-Cretaceous Mass Extinction

    PubMed Central

    Aberhan, Martin; Kiessling, Wolfgang

    2014-01-01

    We analysed field-collected quantitative data of benthic marine molluscs across the Cretaceous–Palaeogene boundary in Patagonia to identify patterns and processes of biodiversity reconstruction after the end-Cretaceous mass extinction. We contrast diversity dynamics from nearshore environments with those from offshore environments. In both settings, Early Palaeogene (Danian) assemblages are strongly dominated by surviving lineages, many of which changed their relative abundance from being rare before the extinction event to becoming the new dominant forms. Only a few of the species in the Danian assemblages were newly evolved. In offshore environments, however, two newly evolved Danian bivalve species attained ecological dominance by replacing two ecologically equivalent species that disappeared at the end of the Cretaceous. In both settings, the total number of Danian genera at a locality remained below the total number of late Cretaceous (Maastrichtian) genera at that locality. We suggest that biotic interactions, in particular incumbency effects, suppressed post-extinction diversity and prevented the compensation of diversity loss by originating and invading taxa. Contrary to the total number of genera at localities, diversity at the level of individual fossiliferous horizons before and after the boundary is indistinguishable in offshore environments. This indicates an evolutionary rapid rebound to pre-extinction values within less than ca 0.5 million years. In nearshore environments, by contrast, diversity of fossiliferous horizons was reduced in the Danian, and this lowered diversity lasted for the entire studied post-extinction interval. In this heterogeneous environment, low connectivity among populations may have retarded the recolonisation of nearshore habitats by survivors. PMID:25028930

  19. Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines.

    PubMed

    Ceballos, Gerardo; Ehrlich, Paul R; Dirzo, Rodolfo

    2017-07-25

    The population extinction pulse we describe here shows, from a quantitative viewpoint, that Earth's sixth mass extinction is more severe than perceived when looking exclusively at species extinctions. Therefore, humanity needs to address anthropogenic population extirpation and decimation immediately. That conclusion is based on analyses of the numbers and degrees of range contraction (indicative of population shrinkage and/or population extinctions according to the International Union for Conservation of Nature) using a sample of 27,600 vertebrate species, and on a more detailed analysis documenting the population extinctions between 1900 and 2015 in 177 mammal species. We find that the rate of population loss in terrestrial vertebrates is extremely high-even in "species of low concern." In our sample, comprising nearly half of known vertebrate species, 32% (8,851/27,600) are decreasing; that is, they have decreased in population size and range. In the 177 mammals for which we have detailed data, all have lost 30% or more of their geographic ranges and more than 40% of the species have experienced severe population declines (>80% range shrinkage). Our data indicate that beyond global species extinctions Earth is experiencing a huge episode of population declines and extirpations, which will have negative cascading consequences on ecosystem functioning and services vital to sustaining civilization. We describe this as a "biological annihilation" to highlight the current magnitude of Earth's ongoing sixth major extinction event.

  20. Determining the Central Atlantic Magmatic Province (CAMPS)'s Role in the Increased Flux of CO2 in the end-Triassic Mass Extinction

    NASA Astrophysics Data System (ADS)

    Srinivasan, P. S.; Bachan, A.; Stanford School of Earth Sciences Department of Paleobiology

    2011-12-01

    The Central Atlantic Magmatic Province (CAMP) is one of the largest flood basalt provinces known. Its empacement coincided with a period of major plant and animal extinctions-the end-Triassic mass extinction. It is postulated that the release of large amounts of carbon dioxide into the atmosphere from the volcanics was one of the causes of this mass extinction. However,the magnitude of impact on ocean chemistry, and timescales involved remain unclear. To determine CAMP's role in this increased flux of CO2, we studied the geochemistry of samples of rock from the Triassic-Jurassic boundary, in northern Italy. Specifically, by observing the ratios of carbon isotopes 12 and 13 in the organic carbon found in these limestone sedimentary rocks, we could determine the ratio of carbonate to organic burial fluxes globally. We drilled limestone rocks from two different sections in the Southern Alps-- Pozzo Glaciale and Val Adrara. Once they were drilled to a fine powder-like form, we acidified the CaCO3 with HCl to isolate the organic carbon. Then, the organic matter was cleaned to rid the acid, and eventually was placed into tin foil to be placed into the Elemental Analyzer, which determined the percent Carbon in each sample. We tested about 200 samples, and placed them into the Mass Spectrometer machine to determine the isotopic ratios of C12 and C13. According to the data, there was a positive excursion for both sample sets, which means that there was an increase in the amount of C13 in the organic matter. The duration of this excursion was at least a few hundred thousand years. This suggests a protracted increase in the burial flux of organic carbon globally, which is consistent with the hypothesized volcanically driven increase in CO2. This further bolsters the contention that CAMP was responsible, in part, for this mass extinction. By studying the earth's recovery from increased carbon fluxes in the past, we can predict the recovery path that our anthropogenically

  1. Are periodic bombardments real?

    NASA Technical Reports Server (NTRS)

    Weissman, Paul R.

    1990-01-01

    Consideration is given to the hypothesis that showers of comets or asteroids strike the earth every 26 m yrs, causing climatic castastrophes and mass extinctions (Raup and Sepkoski, 1984). Possible explanations for the alleged periodicity are discussed, including the possibility that the sun has a small faint companion star and perturbations of the Oort cloud as the solar system passes through the Galactic plane. Also, the possible causes of the extinction at the K-T boundary are examined. The implications of these theories are noted and evidence suggesting that impacts do not have periodicity is presented.

  2. Post-Extinction Ecological Recovery of Marine Life Modes

    NASA Astrophysics Data System (ADS)

    Park, C.; de la Torre, N. G.; Heim, N.; Payne, J.

    2016-12-01

    A mass extinction is defined by a substantial increase in extinction rates, resulting in a loss of taxonomic and ecological diversity. Bush et al. (2007) defined ecological life modes as the feeding, motility, and tiering habits and organized them in a six-by-six "eco-cube" in which each section represented a life mode. In our research, we analyzed the ecological recovery of each life mode after the five mass extinctions. Using a fossil marine genera database, we compiled five heat maps that depict the recovery of the life modes by plotting the diversity of genera in each life mode two intervals before and five intervals after each mass extinction interval. New life modes seem to appear either immediately following or three or more intervals after a mass extinction, which indicates that ecological recovery is not a gradual process, but rather occurs in a punctuated manner. Furthermore, the "filling order" of new life modes differ in each extinction. However, some seem to have defined patterns, such as the Ordovician, where earlier post-extinction intervals experienced an increase in the diversity of erect (tiering) ecospaces, followed by that of surficial and shallow infaunal life modes. The Devonian mass extinction followed a similar pattern as the end Ordovician where erect organisms came first followed by surficial, deep-infaunal, and pelagic life modes. Conversely, intervals following the end-Permian mass extinction experienced a recovery in pelagic, freely-moving life modes, followed by a recovery in infaunal organisms and an explosion in semi-infaunal, erect, surficial, and pelagic ecospaces in the Ladinian. New life modes in the Triassic and Cretaceous mass extinctions did not seem to generate in a distinct pattern. Overall, we conclude that recovery patterns are unique depending on the cause of each mass extinction, and that any general tendency in post-extinction ecological recovery was most likely overridden by the environmental condition of the recovery

  3. Rewinding the process of mammalian extinction.

    PubMed

    Saragusty, Joseph; Diecke, Sebastian; Drukker, Micha; Durrant, Barbara; Friedrich Ben-Nun, Inbar; Galli, Cesare; Göritz, Frank; Hayashi, Katsuhiko; Hermes, Robert; Holtze, Susanne; Johnson, Stacey; Lazzari, Giovanna; Loi, Pasqualino; Loring, Jeanne F; Okita, Keisuke; Renfree, Marilyn B; Seet, Steven; Voracek, Thomas; Stejskal, Jan; Ryder, Oliver A; Hildebrandt, Thomas B

    2016-07-01

    With only three living individuals left on this planet, the northern white rhinoceros (Ceratotherium simum cottoni) could be considered doomed for extinction. It might still be possible, however, to rescue the (sub)species by combining novel stem cell and assisted reproductive technologies. To discuss the various practical options available to us, we convened a multidisciplinary meeting under the name "Conservation by Cellular Technologies." The outcome of this meeting and the proposed road map that, if successfully implemented, would ultimately lead to a self-sustaining population of an extremely endangered species are outlined here. The ideas discussed here, while centered on the northern white rhinoceros, are equally applicable, after proper adjustments, to other mammals on the brink of extinction. Through implementation of these ideas we hope to establish the foundation for reversal of some of the effects of what has been termed the sixth mass extinction event in the history of Earth, and the first anthropogenic one. Zoo Biol. 35:280-292, 2016. © 2016 The Authors. Zoo Biology published by Wiley Periodicals, Inc. © 2016 The Authors. Zoo Biology published by Wiley Periodicals, Inc.

  4. New Age of Fishes initiated by the Cretaceous-Paleogene mass extinction

    NASA Astrophysics Data System (ADS)

    Sibert, Elizabeth C.; Norris, Richard D.

    2015-07-01

    Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous-Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern "age of fishes."

  5. New Age of Fishes initiated by the Cretaceous-Paleogene mass extinction.

    PubMed

    Sibert, Elizabeth C; Norris, Richard D

    2015-07-14

    Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous-Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern "age of fishes."

  6. New Age of Fishes initiated by the Cretaceous−Paleogene mass extinction

    PubMed Central

    Sibert, Elizabeth C.; Norris, Richard D.

    2015-01-01

    Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous−Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern “age of fishes.” PMID:26124114

  7. Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines

    PubMed Central

    Ceballos, Gerardo; Ehrlich, Paul R.; Dirzo, Rodolfo

    2017-01-01

    The population extinction pulse we describe here shows, from a quantitative viewpoint, that Earth’s sixth mass extinction is more severe than perceived when looking exclusively at species extinctions. Therefore, humanity needs to address anthropogenic population extirpation and decimation immediately. That conclusion is based on analyses of the numbers and degrees of range contraction (indicative of population shrinkage and/or population extinctions according to the International Union for Conservation of Nature) using a sample of 27,600 vertebrate species, and on a more detailed analysis documenting the population extinctions between 1900 and 2015 in 177 mammal species. We find that the rate of population loss in terrestrial vertebrates is extremely high—even in “species of low concern.” In our sample, comprising nearly half of known vertebrate species, 32% (8,851/27,600) are decreasing; that is, they have decreased in population size and range. In the 177 mammals for which we have detailed data, all have lost 30% or more of their geographic ranges and more than 40% of the species have experienced severe population declines (>80% range shrinkage). Our data indicate that beyond global species extinctions Earth is experiencing a huge episode of population declines and extirpations, which will have negative cascading consequences on ecosystem functioning and services vital to sustaining civilization. We describe this as a “biological annihilation” to highlight the current magnitude of Earth’s ongoing sixth major extinction event. PMID:28696295

  8. Climatic changes resulting from mass extinctions at the K-T boundary (and other bio-events)

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Volk, Tyler

    1988-01-01

    The mass extinctions at the Cretaceous-Tertiary (K-T) boundary include about 90 percent of marine calcareous nannoplankton (coccoliths), and carbon-isotope data show that marine primary productivity was drastically reduced for about 500,000 years after the boundary event, the so-called Strangelove Ocean effect. One result of the elimination of most marine phytoplankton would have been a severe reduction in production of dimethyl sulfide (DMS), a biogenic gas that is believed to be the major precursor of cloud condensation nuclei (CCN) over the oceans. A drastic reduction in marine CCN should lead to a cloud canopy with significantly lower reflectivity, and hence cause a significant warming at the earth's surface. Calculations suggest that, all other things being held constant, a reduction in CCN of more than 80 percent (a reasonable value for the K-T extinctions) could have produced a rapid global warming of 6 C or more. Oxygen-isotope analyses of marine sediments, and other kinds of paleoclimatic data, have provided for a marked warming, and a general instability of climate coincident with the killoff of marine plankton at the K-T boundary. Similar reductions in phytoplankton abundance at other boundaries, as indicated by marked shifts in carbon-isotope curves, suggest that severe temperature changes may have accompanied other mass extinctions, and raises the intriguing possibility that the extinction events themselves could have contributed to the climatic instabilities at critical bio-events in the geologic record.

  9. The rise of the ruling reptiles and ecosystem recovery from the Permo-Triassic mass extinction.

    PubMed

    Ezcurra, Martín D; Butler, Richard J

    2018-06-13

    One of the key faunal transitions in Earth history occurred after the Permo-Triassic mass extinction ( ca 252.2 Ma), when the previously obscure archosauromorphs (which include crocodylians, dinosaurs and birds) become the dominant terrestrial vertebrates. Here, we place all known middle Permian-early Late Triassic archosauromorph species into an explicit phylogenetic context, and quantify biodiversity change through this interval. Our results indicate the following sequence of diversification: a morphologically conservative and globally distributed post-extinction 'disaster fauna'; a major but cryptic and poorly sampled phylogenetic diversification with significantly elevated evolutionary rates; and a marked increase in species counts, abundance, and disparity contemporaneous with global ecosystem stabilization some 5 million years after the extinction. This multiphase event transformed global ecosystems, with far-reaching consequences for Mesozoic and modern faunas. © 2018 The Author(s).

  10. Biospheric Effects of the Chicxulub Impact and Their Role in the Cretaceous/Tertiary Mass Extinction

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.

    1997-01-01

    A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous/Tertiary (K/T) boundary. The crater size, meteoritic content of the K/T boundary clay, and impact models indicate that the Chicxulub crater was formed by a short period comet or an asteroid impact that released 0.7-3.4 x 10(exp 31) ergs of energy. Impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons (Gt) each of SO2 and water vapor, and over 500 Gt of CO2, were globally distributed in the stratosphere by the impact.

  11. EARTH SCIENCE: Did Volcanoes Drive Ancient Extinctions?

    PubMed

    Kerr, R A

    2000-08-18

    With the publication in recent weeks of two papers on a mass extinction 183 million years ago, researchers can add five suggestive cases to the list of extinctions with known causes. These extinctions coincide with massive outpourings of lava, accompanied by signs that global warming threw the ocean-atmosphere system out of whack. Although no one can yet pin any of these mass extinctions with certainty on the volcanic eruptions, scientists say it's unlikely that they're all coincidences.

  12. Are we in the midst of the sixth mass extinction? A view from the world of amphibians

    PubMed Central

    Wake, David B.; Vredenburg, Vance T.

    2008-01-01

    Many scientists argue that we are either entering or in the midst of the sixth great mass extinction. Intense human pressure, both direct and indirect, is having profound effects on natural environments. The amphibians—frogs, salamanders, and caecilians—may be the only major group currently at risk globally. A detailed worldwide assessment and subsequent updates show that one-third or more of the 6,300 species are threatened with extinction. This trend is likely to accelerate because most amphibians occur in the tropics and have small geographic ranges that make them susceptible to extinction. The increasing pressure from habitat destruction and climate change is likely to have major impacts on narrowly adapted and distributed species. We show that salamanders on tropical mountains are particularly at risk. A new and significant threat to amphibians is a virulent, emerging infectious disease, chytridiomycosis, which appears to be globally distributed, and its effects may be exacerbated by global warming. This disease, which is caused by a fungal pathogen and implicated in serious declines and extinctions of >200 species of amphibians, poses the greatest threat to biodiversity of any known disease. Our data for frogs in the Sierra Nevada of California show that the fungus is having a devastating impact on native species, already weakened by the effects of pollution and introduced predators. A general message from amphibians is that we may have little time to stave off a potential mass extinction. PMID:18695221

  13. Selectivity of end-Cretaceous marine bivalve extinctions

    NASA Technical Reports Server (NTRS)

    Jablonski, D.; Raup, D. M.

    1995-01-01

    Analyses of the end-Cretaceous or Cretaceous-Tertiary mass extinction show no selectivity of marine bivalve genera by life position (burrowing versus exposed), body size, bathymetric position on the continental shelf, or relative breadth of bathymetric range. Deposit-feeders as a group have significantly lower extinction intensities than suspension-feeders, but this pattern is due entirely to low extinction in two groups (Nuculoida and Lucinoidea), which suggests that survivorship was not simply linked to feeding mode. Geographically widespread genera have significantly lower extinction intensities than narrowly distributed genera. These results corroborate earlier work suggesting that some biotic factors that enhance survivorship during times of lesser extinction intensities are ineffectual during mass extinctions.

  14. Using the Theme of Mass Extinctions to Teach Science to Non-Science Major College and University Students

    NASA Astrophysics Data System (ADS)

    Boness, D. A.

    2013-12-01

    The general public is heavily exposed to "news" and commentary---and arts and entertainment---that either inadvertently misrepresents science or even acts to undermine it. Climate change denial and evolution denial is well funded and pervasive. Even university-educated people get little exposure to the aims, methods, debates, and results of scientific inquiry because unless they earn degrees in science they typically only take one or two introductory science courses at the university level. This presentation reports the development of a new, non-science major Seattle University course on mass extinctions throughout earth history. Seattle University is an urban, Jesuit Catholic university. The topic of mass extinctions was chosen for several reasons: (1) To expose the students to a part of current science that has rich historical roots yet by necessity uses methods and reasoning from geology, geophysics, oceanography, physics, chemistry, biology, and astronomy. This multidisciplinary course provides some coverage of sciences that the student would not typically ever see beyond secondary school. (2) To enable the students to learn enough to follow some of the recent and current debates within science (e.g., mass extinctions by asteroid impact versus massive volcanism, ocean anoxia, and ocean acidification), with the students reading some of the actual literature, such as articles in Science, Nature, or Nature Geoscience. (3) To emphasize the importance of "deep time" as evolutionary biological processes interact with massive environmental change over time scales from hundreds of millions of years down to the seconds and hours of an asteroid or comet strike. (4) To show the effects of climate change in the past, present, and future, due to both natural and anthropogenic causes. (5) To help the student critically evaluate the extent to which their future involves a human-caused mass extinction.

  15. Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction

    PubMed Central

    Guex, Jean; Pilet, Sebastien; Müntener, Othmar; Bartolini, Annachiara; Spangenberg, Jorge; Schoene, Blair; Sell, Bryan; Schaltegger, Urs

    2016-01-01

    The temporal coincidence between large igneous provinces (LIPs) and mass extinctions has led many to pose a causal relationship between the two. However, there is still no consensus on a mechanistic model that explains how magmatism leads to the turnover of terrestrial and marine plants, invertebrates and vertebrates. Here we present a synthesis of ammonite biostratigraphy, isotopic data and high precision U-Pb zircon dates from the Triassic-Jurassic (T-J) and Pliensbachian-Toarcian (Pl-To) boundaries demonstrating that these biotic crises are both associated with rapid change from an initial cool period to greenhouse conditions. We explain these transitions as a result of changing gas species emitted during the progressive thermal erosion of cratonic lithosphere by plume activity or internal heating of the lithosphere. Our petrological model for LIP magmatism argues that initial gas emission was dominated by sulfur liberated from sulfide-bearing cratonic lithosphere before CO2 became the dominant gas. This model offers an explanation of why LIPs erupted through oceanic lithosphere are not associated with climatic and biotic crises comparable to LIPs emitted through cratonic lithosphere. PMID:27009463

  16. New theories about ancient extinctions

    USGS Publications Warehouse

    Spall, H.

    1986-01-01

    But all this may be changing. Mass extinctions have been very much in the news in the last few years, triggered in large part by the proposal that the extinction of the dinosaurs and marine animals was caused by a catastrophic collision between the Earth and an extra-terrestrial body (bolide). Recently an equally contentious suggestion has been made that mass extinctions have swept the Earth every 26 to 31 million years for at least the last 250 million years-caused by encounters with some kind of extra-terrestrial object such as one of the asteroids or the comets. 

  17. High-precision U-Pb zircon geochronological constraints on the End-Triassic Mass Extinction, the late Triassic Astronomical Time Scale and geochemical evolution of CAMP magmatism

    NASA Astrophysics Data System (ADS)

    Blackburn, T. J.; Olsen, P. E.; Bowring, S. A.; McLean, N. M.; Kent, D. V.; Puffer, J. H.; McHone, G.; Rasbury, T.

    2012-12-01

    Mass extinction events that punctuate Earth's history have had a large influence on the evolution, diversity and composition of our planet's biosphere. The approximate temporal coincidence between the five major extinction events over the last 542 million years and the eruption of Large Igneous Provinces (LIPs) has led to the speculation that climate and environmental perturbations generated by the emplacement of a large volume of magma in a short period of time triggered each global biologic crisis. Establishing a causal link between extinction and the onset and tempo of LIP eruption has proved difficult because of the geographic separation between LIP volcanic deposits and stratigraphic sequences preserving evidence of the extinction. In most cases, the uncertainties on available radioisotopic dates used to correlate between geographically separated study areas often exceed the duration of both the extinction interval and LIP volcanism by an order of magnitude. The "end-Triassic extinction" (ETE) is one of the "big five" and is characterized by the disappearance of several terrestrial and marine species and dominance of Dinosaurs for the next 134 million years. Speculation on the cause has centered on massive climate perturbations thought to accompany the eruption of flood basalts related to the Central Atlantic Magmatic Province (CAMP), the most aerially extensive and volumetrically one of the largest LIPs on Earth. Despite an approximate temporal coincidence between extinction and volcanism, there lacks evidence placing the eruption of CAMP prior to or at the initiation of the extinction. Estimates of the timing and/or duration of CAMP volcanism provided by astrochronology and Ar-Ar geochronology differ by an order of magnitude, precluding high-precision tests of the relationship between LIP volcanism and the mass extinction, the causes of which are dependent upon the rate of magma eruption. Here we present high precision zircon U-Pb ID-TIMS geochronologic data

  18. Cumulative frequency distribution of past species extinctions

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1991-01-01

    Analysis of Sepkoski's compendium of the time ranges of 30,000+ taxa yields a mean duration of 28.4 ma for genera of fossil invertebrates. This converts to an average extinction rate of 3.5 percent per million years or about one percent every 286,000 years. Using survivorship techniques, these estimates can be converted to the species level, yielding a Phanerozoic average of one percent species extinction every 40,000 years. Variation in extinction rates through time is far greater than the null expectation of a homogeneous birth-death model and this reflects the well-known episodicity of extinction ranging from a few large mass extinctions to so-called background extinction. The observed variation in rates can be used to construct a cumulative frequency distribution of extinction intensity, and this distribution, in the form of a kill curve for species, shows the expected waiting times between extinction events of a given intensity. The kill curve is an average description of the extinction events of a given intensity. The kill curve is an average description of the extinction record and does not imply any cause or causes of extinction. The kill curve shows, among other things, that only about five percent of total species extinctions in the Phanerozoic were involved in the five largest mass extinctions. The other 95 percent were distributed among large and small events not normally called mass extinctions. As an exploration of the possibly absurd proposition that most past extinctions were produced by the effects of large-body impact, the kill curve for species was mapped on the comparable distribution for comet and asteroid impacts. The result is a curve predicting the species kill for a given size of impacting object (expressed as crater size). The results are reasonable in that impacts producing craters less than 30 km (diameter) cause negligible extinction but those producing craters 100-150 km (diameter) cause extinction of species in the range of 45

  19. Recovery and diversification of marine communities following the late Permian mass extinction event in the western Palaeotethys

    NASA Astrophysics Data System (ADS)

    Foster, William J.; Sebe, Krisztina

    2017-08-01

    The recovery of benthic invertebrates following the late Permian mass extinction event is often described as occurring in the Middle Triassic associated with the return of Early Triassic Lazarus taxa, increased body sizes, platform margin metazoan reefs, and increased tiering. Most quantitative palaeoecological studies, however, are limited to the Early Triassic and the timing of the final phase of recovery is rarely quantified. Here, quantitative abundance data of benthic invertebrates were collected from the Middle Triassic (Anisian) succession of the Mecsek Mountains (Hungary), and analysed with univariate and multivariate statistics to investigate the timing of recovery following the late Permian mass extinction. These communities lived in a mixed siliciclastic-carbonate ramp setting on the western margin of the Palaeotethys Ocean. The new data presented here is combined with the previously studied Lower Triassic succession of the Aggtelek Karst (Hungary), which records deposition of comparable facies and in the same region of the Palaeotethys Ocean. The Middle Triassic benthic fauna can be characterised by three distinct ecological states. The first state is recorded in the Viganvár Limestone Formation representing mollusc-dominated communities restricted to above wave base, which are comparable to the lower and mid-Spathian Szin Marl Formation faunas. The second state is recorded in the Lapis Limestone Formation and records extensive bioturbation that is not limited to wave base and is comparable to the upper Spathian Szinpetri Limestone Formation. The third ecological state occurs in the Zuhánya Limestone Formation which was deposited in the Pelsonian Binodosus Zone, and has a more 'Palaeozoic' structure with sessile brachiopods dominating assemblages for the first time in the Mesozoic. The return of community-level characteristics to pre-extinction levels and the diversification of invertebrates suggests that the final stages of recovery and the radiation

  20. Uranium isotope evidence for the abrupt onset of oceanic anoxia during the end-Guadalupian mass extinction

    NASA Astrophysics Data System (ADS)

    Song, H.; Algeo, T. J.; Romaniello, S. J.; Tong, J.; Du, Y.; Wei, H.; Shen, S.; Anbar, A. D.

    2016-12-01

    The end-Guadalupian (Middle/Late Permian) mass extinction was one of the major crises of the Phanerozoic, resulting in the disappearance of numerous shallow-marine taxa. Several hypotheses have been proposed for this catastrophe but are still under debate. Here, we undertook a high-resolution carbonate U isotopic (δ238/235U) study of the Guadalupian-Lopingian boundary (GLB) at the Penglaitan section (Guadalupian/ Lopingian GSSP) to explore the causal relationship between ocean redox changes and the mass extinction event. The Penglaitan δ238U profile shows two abrupt negative excursions, one in the uppermost Guadalupian (Beds 6j-6k) and the other in the lowermost Lopingian (lower Bed 7). The first excursion (from ‒0.30 ‰ to ‒0.50 ‰) coincided with the main extinction event, suggesting that rapid expansion of oceanic anoxia may have been a contributor to the biotic crisis. The second, larger excursion (from ‒0.25 ‰ to ‒0.65 ‰) demonstrates that the crisis interval was marked by multiple phases of expanded oceanic anoxia. A U-isotope mass balance model shows that, during these excursions, the anoxic/euxinic sink flux increased to 40 % of the total sink flux of seawater U, which is three times of the modern ocean value of 13 %. This study thus provides circumstantial evidence for a causal relationship between expansion of oceanic anoxia and the end-Guadalupian biotic crisis.

  1. What can experimental geobiology tell us about mass extinctions, past, present and future?

    NASA Astrophysics Data System (ADS)

    Bond, David

    2017-04-01

    We know more than ever about the causes and consequences of Earth's greatest mass extinctions thanks to much improved resolution in the fossil record, dating, and proxies for palaeoenvironmental change. Despite much progress, there is no consensus on what drives ecosystems to collapse. The realisation that Earth is again facing stresses implicated in its past crises (e.g. proximal kill mechanisms such as global warming, ocean acidification and anoxia) has intensified research on the ultimate cause(s) of extinctions (e.g. large igneous provinces and bolide impacts). However, the links between proximal kill mechanisms and their drivers remains poorly understood. Here I evaluate environmental factors implicated in major episodes of species extinctions and explores the mechanistic links by which they did their damage. Experimental geobiology is beginning to unlock the secrets of past crises by examining responses of species to change. Reduced pH, for instance alters the efficacy of fishes' chemical receptors, leaving them less equipped to detect prey, predators and mates - invoking "death-by-celibacy" scenarios. Elevated atmospheric CO2 induces hypercapnic stress (as well as being the root cause of ocean acidification). Prolonged exposure to anoxia causes death without selectivity. Global warming induces a multitude of stresses, primarily linked to increased metabolic rate according to the Q10 law. Experimental geobiologists and Earth scientists could together unravel the causes of past extinctions, better inform understanding of the modern crisis and our approach to the future.

  2. The Effect of Size and Ecology on Extinction Susceptibility

    NASA Astrophysics Data System (ADS)

    Huynh, C.; Yuan, A.; Heim, N.; Payne, J.

    2015-12-01

    Although life on Earth first emerged as prokaryotic organisms, it eventually evolved into billions of different species. However, extinctions on Earth, especially the five mass extinctions, have decimated species. So what leads to a species survival or demise during a mass extinction? Are certain species more susceptible to extinctions based on their size and ecology? For this project, we focused on the data of marine animals. To examine the impact of size and ecology on a species's likelihood of survival, we compared the sizes and ecologies of the survivors and victims of the five mass extinctions. The ecology, or life mode, of a genus consists of the combination of tiering, motility, and feeding mechanism. Tiering refers to the animal's typical location in the water column and sediments, motility refers to its ability to move, and feeding mechanism describes the way the organism eats; together, they describe the animal's behavior. We analyzed the effect of ecology on survival using logistic regression, which compares life mode to the success or failure of a genus during each mass extinction interval. For organism size, we found the extinct organisms' mean size (both volume and length) and compared it with the average size of survivors on a graph. Our results show that while surviving genera of mass extinctions tended to be slightly larger than those that went extinct, there was no significant difference. Even though the Permian (Changhsingian) and Triassic (Rhaetian) extinctions had larger surviving species, likewise the difference was small. Ecology had a more obvious impact on the likelihood of survival; fast-moving, predatory pelagic organisms were the most likely to go extinct, while sedentary, infaunal suspension feeders had the greatest chances of survival. Overall, ecology played a greater role than size in determining the survival of a species. With this information, we can use ecology to predict which species would survive future extinctions.

  3. End-Permian Mass Extinction in the Oceans: An Ancient Analog for the Twenty-First Century?

    NASA Astrophysics Data System (ADS)

    Payne, Jonathan L.; Clapham, Matthew E.

    2012-05-01

    The greatest loss of biodiversity in the history of animal life occurred at the end of the Permian Period (˜252 million years ago). This biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of Earth's largest continental flood basalt provinces, the Siberian Traps. Volatile release from basaltic magma and sedimentary strata during emplacement of the Siberian Traps can account for most end-Permian paleontological and geochemical observations. Climate change and, perhaps, destruction of the ozone layer can explain extinctions on land, whereas changes in ocean oxygen levels, CO2, pH, and temperature can account for extinction selectivity across marine animals. These emerging insights from geology, geochemistry, and paleobiology suggest that the end-Permian extinction may serve as an important ancient analog for twenty-first century oceans.

  4. Is IR going extinct?

    PubMed

    Mitchell, Audra

    2017-03-01

    A global extinction crisis may threaten the survival of most existing life forms. Influential discourses of 'existential risk' suggest that human extinction is a real possibility, while several decades of evidence from conservation biology suggests that the Earth may be entering a 'sixth mass extinction event'. These conditions threaten the possibilities of survival and security that are central to most branches of International Relations. However, this discipline lacks a framework for addressing (mass) extinction. From notions of 'nuclear winter' and 'omnicide' to contemporary discourses on catastrophe, International Relations thinking has treated extinction as a superlative of death. This is a profound category mistake: extinction needs to be understood not in the ontic terms of life and death, but rather in the ontological context of be(com)ing and negation. Drawing on the work of theorists of the 'inhuman' such as Quentin Meillassoux, Claire Colebrook, Ray Brassier, Jean-Francois Lyotard and Nigel Clark, this article provides a pathway for thinking beyond existing horizons of survival and imagines a profound transformation of International Relations. Specifically, it outlines a mode of cosmopolitics that responds to the element of the inhuman and the forces of extinction. Rather than capitulating to narratives of tragedy, this cosmopolitics would make it possible to think beyond the restrictions of existing norms of 'humanity' to embrace an ethics of gratitude and to welcome the possibility of new worlds, even in the face of finitude.

  5. Is IR going extinct?

    PubMed Central

    Mitchell, Audra

    2016-01-01

    A global extinction crisis may threaten the survival of most existing life forms. Influential discourses of ‘existential risk’ suggest that human extinction is a real possibility, while several decades of evidence from conservation biology suggests that the Earth may be entering a ‘sixth mass extinction event’. These conditions threaten the possibilities of survival and security that are central to most branches of International Relations. However, this discipline lacks a framework for addressing (mass) extinction. From notions of ‘nuclear winter’ and ‘omnicide’ to contemporary discourses on catastrophe, International Relations thinking has treated extinction as a superlative of death. This is a profound category mistake: extinction needs to be understood not in the ontic terms of life and death, but rather in the ontological context of be(com)ing and negation. Drawing on the work of theorists of the ‘inhuman’ such as Quentin Meillassoux, Claire Colebrook, Ray Brassier, Jean-Francois Lyotard and Nigel Clark, this article provides a pathway for thinking beyond existing horizons of survival and imagines a profound transformation of International Relations. Specifically, it outlines a mode of cosmopolitics that responds to the element of the inhuman and the forces of extinction. Rather than capitulating to narratives of tragedy, this cosmopolitics would make it possible to think beyond the restrictions of existing norms of ‘humanity’ to embrace an ethics of gratitude and to welcome the possibility of new worlds, even in the face of finitude. PMID:29708126

  6. Are marine and nonmarine extinctions correlated?

    NASA Astrophysics Data System (ADS)

    Rampino, Michael R.

    Recent papers in Eos have debated the possible relationships between marine mass extinctions, comet showers, and volcanism [Alvarez, 1986; Officer and Grieve, 1986], and ail three might be linked [Rampino, 1987]. Moreover, as Officer and Grieve [ 1986] point out, various other causes have been suggested for given extinction events, including changes in climate, ocean circulation, and sea level fluctuations, possibly related to plate tectonics and continental positions. Also under debate is the issue of whether mass extinctions were gradual, stepped, or geologically sudden events (see, for example, Hut et al. [1987]). A missing ingredient thus far in these debates has been the record of faunal diversity of nonmarine animals. Does this show any agreement with the marine extinction record?

  7. Chemical compositions and reconstructed light extinction coefficients of particulate matter in a mega-city in the western Yangtze River Delta, China

    NASA Astrophysics Data System (ADS)

    Shen, Guofeng; Xue, Miao; Yuan, Siyu; Zhang, Jie; Zhao, Qiuyue; Li, Bing; Wu, Haisuo; Ding, Aijun

    2014-02-01

    Ambient particulate matter was collected in a megacity, Nanjing in western YRD during the spring and summer periods. Chemical compositions of fine PM including organic carbon, elemental carbon, elements and water soluble ions were analyzed. The light extinction coefficients were reconstructed following the IMPROVE formula. Organic matter was the most abundant composition in PM2.5 (20-25% of total mass), followed by the inorganic ions. During the spring time, geological materials contributed 25% of the total PM2.5. Estimated light extinction coefficient ranged from 133 to 560 Mm-1 with the deciview haze index value of 26-40 dv, indicating strong light extinction by PM and subsequently low visibility in the city. Reconstructed ammonium sulfate, ammonium nitrate, organic matter and light absorption carbon in fine PM contributed significantly (37 ± 10, 16 ± 6, 15 ± 4 and 10 ± 3%, respectively) to the total light extinction of PM, while soil (5-7%) and sea salt fractions (2-4%) in fine PM and coarse PM (6-11%) had relatively minor influences. The results of backward air trajectory showed that the site was strongly influenced by the air from the eastern (39%) and southeastern (29%) areas during the sampling period. Air plumes from the Southeastern had both high PM mass pollution and large light extinction, while the air mass originating from the Northwestern resulted in high PM mass loading but relatively lower light extinction.

  8. Bioessential element-depleted ocean following the euxinic maximum of the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Takahashi, Satoshi; Yamasaki, Shin-ichi; Ogawa, Yasumasa; Kimura, Kazuhiko; Kaiho, Kunio; Yoshida, Takeyoshi; Tsuchiya, Noriyoshi

    2014-05-01

    We describe variations in trace element compositions that occurred on the deep seafloor of palaeo-superocean Panthalassa during the end-Permian mass extinction based on samples of sedimentary rock from one of the most continuous Permian-Triassic boundary sections of the pelagic deep sea exposed in north-eastern Japan. Our measurements revealed low manganese (Mn) enrichment factor (normalised by the composition of the average upper continental crust) and high cerium anomaly values throughout the section, suggesting that a reducing condition already existed in the depositional environment in the Changhsingian (Late Permian). Other redox-sensitive trace-element (vanadium [V], chromium [Cr], molybdenum [Mo], and uranium [U]) enrichment factors provide a detailed redox history ranging from the upper Permian to the end of the Permian. A single V increase (representing the first reduction state of a two-step V reduction process) detected in uppermost Changhsingian chert beds suggests development into a mildly reducing deep-sea condition less than 1 million years before the end-Permian mass extinction. Subsequently, a more reducing condition, inferred from increases in Cr, V, and Mo, developed in overlying Changhsingian grey siliceous claystone beds. The most reducing sulphidic condition is recognised by the highest peaks of Mo and V (second reduction state) in the uppermost siliceous claystone and overlying lowermost black claystone beds, in accordance with the end-Permian mass extinction event. This significant increase in Mo in the upper Changhsingian led to a high Mo/U ratio, much larger than that of modern sulphidic ocean regions. This trend suggests that sulphidic water conditions developed both at the sediment-water interface and in the water column. Above the end-Permian mass extinction horizon, Mo, V and Cr decrease significantly. On this trend, we provide an interpretation of drawdown of these elements in seawater after the massive element precipitation event

  9. Giant comets and mass extinctions of life

    NASA Astrophysics Data System (ADS)

    Napier, W. M.

    2015-03-01

    I find evidence for clustering in age of well-dated impact craters over the last 500 Myr. At least nine impact episodes are identified, with durations whose upper limits are set by the dating accuracy of the craters. Their amplitudes and frequency are inconsistent with an origin in asteroid breakups or Oort cloud disturbances, but are consistent with the arrival and disintegration in near-Earth orbits of rare, giant comets, mainly in transit from the Centaur population into the Jupiter family and Encke regions. About 1 in 10 Centaurs in Chiron-like orbits enter Earth-crossing epochs, usually repeatedly, each such epoch being generally of a few thousand years' duration. On time-scales of geological interest, debris from their breakup may increase the mass of the near-Earth interplanetary environment by two or three orders of magnitude, yielding repeated episodes of bombardment and stratospheric dusting. I find a strong correlation between these bombardment episodes and major biostratigraphic and geological boundaries, and propose that episodes of extinction are most effectively driven by prolonged encounters with meteoroid streams during bombardment episodes. Possible mechanisms are discussed.

  10. Explosive eruption of coal and basalt and the end-Permian mass extinction

    PubMed Central

    Ogden, Darcy E.; Sleep, Norman H.

    2012-01-01

    The end-Permian extinction decimated up to 95% of carbonate shell-bearing marine species and 80% of land animals. Isotopic excursions, dissolution of shallow marine carbonates, and the demise of carbonate shell-bearing organisms suggest global warming and ocean acidification. The temporal association of the extinction with the Siberia flood basalts at approximately 250 Ma is well known, and recent evidence suggests these flood basalts may have mobilized carbon in thick deposits of organic-rich sediments. Large isotopic excursions recorded in this period are potentially explained by rapid venting of coal-derived methane, which has primarily been attributed to metamorphism of coal by basaltic intrusion. However, recently discovered contemporaneous deposits of fly ash in northern Canada suggest large-scale combustion of coal as an additional mechanism for rapid release of carbon. This massive coal combustion may have resulted from explosive interaction with basalt sills of the Siberian Traps. Here we present physical analysis of explosive eruption of coal and basalt, demonstrating that it is a viable mechanism for global extinction. We describe and constrain the physics of this process including necessary magnitudes of basaltic intrusion, mixing and mobilization of coal and basalt, ascent to the surface, explosive combustion, and the atmospheric rise necessary for global distribution. PMID:22184229

  11. Greenhouse-icehouse transition in the Late Ordovician marks a step change in extinction regime in the marine plankton.

    PubMed

    Crampton, James S; Cooper, Roger A; Sadler, Peter M; Foote, Michael

    2016-02-09

    Two distinct regimes of extinction dynamic are present in the major marine zooplankton group, the graptolites, during the Ordovician and Silurian periods (486-418 Ma). In conditions of "background" extinction, which dominated in the Ordovician, taxonomic evolutionary rates were relatively low and the probability of extinction was highest among newly evolved species ("background extinction mode"). A sharp change in extinction regime in the Late Ordovician marked the onset of repeated severe spikes in the extinction rate curve; evolutionary turnover increased greatly in the Silurian, and the extinction mode changed to include extinction that was independent of species age ("high-extinction mode"). This change coincides with a change in global climate, from greenhouse to icehouse conditions. During the most extreme episode of extinction, the Late Ordovician Mass Extinction, old species were selectively removed ("mass extinction mode"). Our analysis indicates that selective regimes in the Paleozoic ocean plankton switched rapidly (generally in <0.5 My) from one mode to another in response to environmental change, even when restoration of the full ecosystem was much slower (several million years). The patterns observed are not a simple consequence of geographic range effects or of taxonomic changes from Ordovician to Silurian. Our results suggest that the dominant primary controls on extinction throughout the lifespan of this clade were abiotic (environmental), probably mediated by the microphytoplankton.

  12. Greenhouse−icehouse transition in the Late Ordovician marks a step change in extinction regime in the marine plankton

    PubMed Central

    Crampton, James S.; Cooper, Roger A.; Sadler, Peter M.; Foote, Michael

    2016-01-01

    Two distinct regimes of extinction dynamic are present in the major marine zooplankton group, the graptolites, during the Ordovician and Silurian periods (486−418 Ma). In conditions of “background” extinction, which dominated in the Ordovician, taxonomic evolutionary rates were relatively low and the probability of extinction was highest among newly evolved species (“background extinction mode”). A sharp change in extinction regime in the Late Ordovician marked the onset of repeated severe spikes in the extinction rate curve; evolutionary turnover increased greatly in the Silurian, and the extinction mode changed to include extinction that was independent of species age (“high-extinction mode”). This change coincides with a change in global climate, from greenhouse to icehouse conditions. During the most extreme episode of extinction, the Late Ordovician Mass Extinction, old species were selectively removed (“mass extinction mode”). Our analysis indicates that selective regimes in the Paleozoic ocean plankton switched rapidly (generally in <0.5 My) from one mode to another in response to environmental change, even when restoration of the full ecosystem was much slower (several million years). The patterns observed are not a simple consequence of geographic range effects or of taxonomic changes from Ordovician to Silurian. Our results suggest that the dominant primary controls on extinction throughout the lifespan of this clade were abiotic (environmental), probably mediated by the microphytoplankton. PMID:26811471

  13. [Reconstructed ambient light extinction coefficient and its contribution factors in Beijing in January, 2010].

    PubMed

    Zhu, Li-Hua; Tao, Jun; Chen, Zhong-Ming; Zhao, Yue; Zhang, Ren-Jian; Cao, Jun-Ji

    2012-01-01

    Aerosol samples for PM2.5 were collected from 1st January to 31st January 2010, in Beijing. The concentrations of organic carbon, elemental carbon, water-solubile ions and soil elements of all particle samples were determined by thermal/optical carbon analyzer, ion chromatography and X-ray fluorescence spectrometer, respectively. The scattering coefficients (b(sp)), absorbing coefficients (b(ap)) and meteorological parameters for this period were also measured. Ambient light extinction coefficients were reconstructed by IMPROVE formula and were compared with measured light extinction coefficients. The results showed that the average mass concentration of PM2.5 was (144.3 +/- 89.1) microg x m(-3) during campaigning period. The average values of measured b(ap), b(sp) and extinction coefficient (b(ext)) were (67.4 +/- 54.3), (328.5 +/- 353.8) and (395.9 +/- 405.2) Mm(-1), respectively. IMPROVE formula is suitable for source apportionment of light extinction coefficient in campaign period. The average value of calculated b'(ext) was (611 +/- 503) Mm(-1) in January, 2010. The major contributors to ambient light extinction coefficients included (NH4) 2SO4 (24.6%), NH4NO3 (11.6%), OM (45.5%), EC (11.9%) and FS (6.4%), respectively.

  14. High-precision timeline for Earth's most severe extinction.

    PubMed

    Burgess, Seth D; Bowring, Samuel; Shen, Shu-zhong

    2014-03-04

    The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms.

  15. Colloquium paper: are we in the midst of the sixth mass extinction? A view from the world of amphibians.

    PubMed

    Wake, David B; Vredenburg, Vance T

    2008-08-12

    Many scientists argue that we are either entering or in the midst of the sixth great mass extinction. Intense human pressure, both direct and indirect, is having profound effects on natural environments. The amphibians--frogs, salamanders, and caecilians--may be the only major group currently at risk globally. A detailed worldwide assessment and subsequent updates show that one-third or more of the 6,300 species are threatened with extinction. This trend is likely to accelerate because most amphibians occur in the tropics and have small geographic ranges that make them susceptible to extinction. The increasing pressure from habitat destruction and climate change is likely to have major impacts on narrowly adapted and distributed species. We show that salamanders on tropical mountains are particularly at risk. A new and significant threat to amphibians is a virulent, emerging infectious disease, chytridiomycosis, which appears to be globally distributed, and its effects may be exacerbated by global warming. This disease, which is caused by a fungal pathogen and implicated in serious declines and extinctions of >200 species of amphibians, poses the greatest threat to biodiversity of any known disease. Our data for frogs in the Sierra Nevada of California show that the fungus is having a devastating impact on native species, already weakened by the effects of pollution and introduced predators. A general message from amphibians is that we may have little time to stave off a potential mass extinction.

  16. Series cell light extinction monitor

    DOEpatents

    Novick, Vincent J.

    1990-01-01

    A method and apparatus for using the light extinction measurements from two or more light cells positioned along a gasflow chamber in which the gas volumetric rate is known to determine particle number concentration and mass concentration of an aerosol independent of extinction coefficient and to determine estimates for particle size and mass concentrations. The invention is independent of particle size. This invention has application to measurements made during a severe nuclear reactor fuel damage test.

  17. Structural changes of marine communities over the Permian-Triassic transition: Ecologically assessing the end-Permian mass extinction and its aftermath

    NASA Astrophysics Data System (ADS)

    Chen, Zhong-Qiang; Tong, Jinnan; Liao, Zhuo-Ting; Chen, Jing

    2010-08-01

    The Permian/Triassic (P/Tr) transition is ecologically assessed based on examining 23 shelly communities from five shallow platform, ramp and shelf basin facies Permian-Triassic boundary (PTB) sections in South China. The shelly communities have undergone two major collapses coinciding with the two episodes of the end-Permian mass extinction. The first P/Tr extinction event devastated shelly communities in all types of settings to some extent. The basin communities have been more severely impacted than both platform and ramp communities. The survival faunas have rebounded more rapidly in shallow niches than in relatively deep habitats. The second P/Tr crisis destroyed the survival communities in shallow setting and had little impact on the basin communities in terms of community structures. The early Griesbachian communities are overall low-diversity and high-dominance. The governorship switch from brachiopods to bivalves in marine communities has been facilitated by two pulses of the end-Permian mass extinction and the whole takeover process took about 200 ka across the P/Tr boundary. Bivalve ecologic takeover initially occurred immediately after the first P/Tr extinction in shallow water habitats and was eventually completed in all niches after the second P/Tr event. Some post-extinction communities have the irregular rarefaction curves due to the unusual community structures rather than sampling intensities.

  18. Biogeography of worm lizards (Amphisbaenia) driven by end-Cretaceous mass extinction

    PubMed Central

    Longrich, Nicholas R.; Vinther, Jakob; Pyron, R. Alexander; Pisani, Davide; Gauthier, Jacques A.

    2015-01-01

    Worm lizards (Amphisbaenia) are burrowing squamates that live as subterranean predators. Their underground existence should limit dispersal, yet they are widespread throughout the Americas, Europe and Africa. This pattern was traditionally explained by continental drift, but molecular clocks suggest a Cenozoic diversification, long after the break-up of Pangaea, implying dispersal. Here, we describe primitive amphisbaenians from the North American Palaeocene, including the oldest known amphisbaenian, and provide new and older molecular divergence estimates for the clade, showing that worm lizards originated in North America, then radiated and dispersed in the Palaeogene following the Cretaceous-Palaeogene (K-Pg) extinction. This scenario implies at least three trans-oceanic dispersals: from North America to Europe, from North America to Africa and from Africa to South America. Amphisbaenians provide a striking case study in biogeography, suggesting that the role of continental drift in biogeography may be overstated. Instead, these patterns support Darwin and Wallace's hypothesis that the geographical ranges of modern clades result from dispersal, including oceanic rafting. Mass extinctions may facilitate dispersal events by eliminating competitors and predators that would otherwise hinder establishment of dispersing populations, removing biotic barriers to dispersal. PMID:25833855

  19. Retrieval and Reconsolidation Accounts of Fear Extinction

    PubMed Central

    Ponnusamy, Ravikumar; Zhuravka, Irina; Poulos, Andrew M.; Shobe, Justin; Merjanian, Michael; Huang, Jeannie; Wolvek, David; O’Neill, Pia-Kelsey; Fanselow, Michael S.

    2016-01-01

    Extinction is the primary mode for the treatment of anxiety disorders. However, extinction memories are prone to relapse. For example, fear is likely to return when a prolonged time period intervenes between extinction and a subsequent encounter with the fear-provoking stimulus (spontaneous recovery). Therefore there is considerable interest in the development of procedures that strengthen extinction and to prevent such recovery of fear. We contrasted two procedures in rats that have been reported to cause such deepened extinction. One where extinction begins before the initial consolidation of fear memory begins (immediate extinction) and another where extinction begins after a brief exposure to the consolidated fear stimulus. The latter is thought to open a period of memory vulnerability similar to that which occurs during initial consolidation (reconsolidation update). We also included a standard extinction treatment and a control procedure that reversed the brief exposure and extinction phases. Spontaneous recovery was only found with the standard extinction treatment. In a separate experiment we tested fear shortly after extinction (i.e., within 6 h). All extinction procedures, except reconsolidation update reduced fear at this short-term test. The findings suggest that strengthened extinction can result from alteration in both retrieval and consolidation processes. PMID:27242459

  20. Isotopic evidence for an anomalously low oceanic sulfate concentration following end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Luo, Genming; Kump, Lee R.; Wang, Yongbiao; Tong, Jinnan; Arthur, Michael A.; Yang, Hao; Huang, Junhua; Yin, Hongfu; Xie, Shucheng

    2010-11-01

    The cataclysmic end-Permian mass extinction was immediately followed by a global expansion of microbial ecosystems, as demonstrated by widespread microbialite sequences (disaster facies) in shallow water settings. Here we present high-resolution carbonate carbon ( δ13C carb) and carbonate-associated sulfate-sulfur isotope ( δ34S CAS) records from the microbialite in the Cili Permian-Triassic (P-Tr) section in South China. A stepwise decline in δ13C carb begins in the underlying skeletal limestone, predating the main oceanic mass extinction and the first appearance of microbialite, and reaches its nadir in the upper part of the microbialite layer. The corresponding δ34S CAS, in the range of 17.4‰ to 27.4‰, is relatively stable in the underlying skeletal limestone, and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite. Two episodes of positive and negative shifts occurred within the microbialite layer, and exhibit a remarkable co-variance of sulfur and carbon isotope composition. The large amplitude of the variation in δ34S CAS, as high as 7‰ per 100 kiloyears, suggests a small oceanic sulfate reservoir size at this time. Furthermore, the δ13C carb and δ34S CAS records co-vary without phase lag throughout the microbialite interval, implying a marine-driven C cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations. On the basis of a non-steady-state box model, we argue that the oceanic sulfate concentration may have fallen to less than 15%, perhaps as low as 3%, of that in the modern oceans. Low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic/sulfidic conditions prior to the main mass extinction. By promoting methanogenesis and a build-up of atmospheric CH 4 and CO 2, low oceanic sulfate may have intensified global warming, exacerbating the inimical environmental conditions of the latest Permian.

  1. The extinct, giant giraffid Sivatherium giganteum: skeletal reconstruction and body mass estimation

    PubMed Central

    2016-01-01

    Sivatherium giganteum is an extinct giraffid from the Plio–Pleistocene boundary of the Himalayan foothills. To date, there has been no rigorous skeletal reconstruction of this unusual mammal. Historical and contemporary accounts anecdotally state that Sivatherium rivalled the African elephant in terms of its body mass, but this statement has never been tested. Here, we present a three-dimensional composite skeletal reconstruction and calculate a representative body mass estimate for this species using a volumetric method. We find that the estimated adult body mass of 1246 kg (857—1812 kg range) does not approach that of an African elephant, but confirms that Sivatherium was certainly a large giraffid, and may have been the largest ruminant mammal that has ever existed. We contrast this volumetric estimate with a bivariate scaling estimate derived from Sivatherium's humeral circumference and find that there is a discrepancy between the two. The difference implies that the humeral circumference of Sivatherium is greater than expected for an animal of this size, and we speculate this may be linked to a cranial shift in centre of mass. PMID:26763212

  2. The extinct, giant giraffid Sivatherium giganteum: skeletal reconstruction and body mass estimation.

    PubMed

    Basu, Christopher; Falkingham, Peter L; Hutchinson, John R

    2016-01-01

    Sivatherium giganteum is an extinct giraffid from the Plio-Pleistocene boundary of the Himalayan foothills. To date, there has been no rigorous skeletal reconstruction of this unusual mammal. Historical and contemporary accounts anecdotally state that Sivatherium rivalled the African elephant in terms of its body mass, but this statement has never been tested. Here, we present a three-dimensional composite skeletal reconstruction and calculate a representative body mass estimate for this species using a volumetric method. We find that the estimated adult body mass of 1246 kg (857-1812 kg range) does not approach that of an African elephant, but confirms that Sivatherium was certainly a large giraffid, and may have been the largest ruminant mammal that has ever existed. We contrast this volumetric estimate with a bivariate scaling estimate derived from Sivatherium's humeral circumference and find that there is a discrepancy between the two. The difference implies that the humeral circumference of Sivatherium is greater than expected for an animal of this size, and we speculate this may be linked to a cranial shift in centre of mass. © 2016 The Authors.

  3. Dinosaur bone beds and mass mortality: Implications for the K-T extinction

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth

    1988-01-01

    Mass accumulations of fossilized large terrestrial vertebrate skeletons (bone beds: BB) provide a test for K-T catastrophic extinction hypotheses. The two major factors contributing to BB formation are mode of death and sedimentation rate. Catastrophic mass mortality (CMM) is the sudden death of numerous individuals where species, age, health, gender, or social ranking offer no survivorship advantage. Noncatastrophic mass mortality (NCMM) occurs over time and is strongly influenced by species, age, or gender. In addition to cause of death, sedimentation rate is also important in BB formation. Models of BBs can be made. The CMM drops all individuals in their tracks, therefore, the BB should reflect the living population with respect to species, age, or gender. The NCMM results in monospecific BBs skewed in the direction of the less fit, usually the very young or very old, or towards a specific gender. The NCMM and AM BBs may become more similar the more spread out over time NCMM deaths occur because carcasses are widely scattered requiring hydraulic accumulation, and the greater time allows for more disarticulation and weathering. The CMM and NCMM BB appear to be dominated by social animals. Applying this and the characteristics of mortality patterns to the uppermost Cretaceous Hell Creek Formation indicates that only NCMM and AM BB occur. Furthermore, NCMM BB are rare in the upper third of the Hell Creek. Near the K-T boundary, only AM BB are known. The absence of CMM and NCMM BB appears to be real reflecting a decrease in population levels of some dinosaurs prior to the K-T event. The absence of CMM suggests that the K-T event did not lead to an instantaneous extinction of dinosaurs. Nor was there a protracted die-off due to an asteroid impact winter, because no NCMM BB are known at or near the K-T boundary.

  4. Anoxia, toxic metals and acidification: volcanically-driven causes of the Middle Permian (Capitanian) mass extinction in NW Pangaea?

    NASA Astrophysics Data System (ADS)

    Bond, David; Grasby, Stephen; Wignall, Paul

    2017-04-01

    The controversial Capitanian (Middle Permian, 262 Ma) mass extinction, mostly known from equatorial latitudes, has recently been identified in a Boreal setting in Spitsbergen. We now document this extinction in the record of brachiopods from the Sverdrup Basin in NW Pangaea (Ellesmere Island, Canada), confirming Middle Permian losses as a global crisis on par with the "Big Five". Redox proxies (pyrite framboids and trace metals) show that the high latitude crisis coincided with an intensification of oxygen-poor conditions - a potent killer that is not clearly developed in lower latitude sections. Mercury becomes briefly enriched in strata at the level of the Middle Permian extinction level in Spitsbergen and Ellesmere Island, indicating voluminous but short-lived volcanism that is likely to have been the emplacement of the Emeishan large igneous province (LIP) in SW China. A potent cocktail of poisons appears to have impacted across the Boreal Realm, whilst the near-total loss of carbonates near the extinction level is also consistent with reduced pH across the region. Multiple stresses, possibly with origins in low-latitude LIP volcanism, are therefore implicated in the Middle Permian extinction and there was no respite even in the far-distant Boreal Realm.

  5. Changes in environmental conditions as the cause of the marine biota Great Mass Extinction at the Triassic-Jurassic boundary

    NASA Astrophysics Data System (ADS)

    Barash, M. S.

    2016-02-01

    In the interval of the Triassic-Jurassic boundary, 80% of the marine species became extinct. Four main hypotheses about the causes of this mass extinction are considered: volcanism, climatic oscillations, sea level variations accompanied by anoxia, and asteroid impact events. The extinction was triggered by an extensive flooding of basalts in the Central Atlantic Magmatic Province. Furthermore, a number of meteoritic craters have been found. Under the effect of cosmic causes, two main sequences of events developed on the Earth: terrestrial ones, leading to intensive volcanism, and cosmic ones (asteroid impacts). Their aftermaths, however, were similar in terms of the chemical compounds and aerosols released. As a consequence, the greenhouse effect, dimming of the atmosphere (impeding photosynthesis), ocean stagnation, and anoxia emerged. Then, biological productivity decreased and food chains were destroyed. Thus, the entire ecosystem was disturbed and a considerable part of the biota became extinct.

  6. High-precision timeline for Earth’s most severe extinction

    PubMed Central

    Burgess, Seth D.; Bowring, Samuel; Shen, Shu-zhong

    2014-01-01

    The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms. PMID:24516148

  7. Biogeography of worm lizards (Amphisbaenia) driven by end-Cretaceous mass extinction.

    PubMed

    Longrich, Nicholas R; Vinther, Jakob; Pyron, R Alexander; Pisani, Davide; Gauthier, Jacques A

    2015-05-07

    Worm lizards (Amphisbaenia) are burrowing squamates that live as subterranean predators. Their underground existence should limit dispersal, yet they are widespread throughout the Americas, Europe and Africa. This pattern was traditionally explained by continental drift, but molecular clocks suggest a Cenozoic diversification, long after the break-up of Pangaea, implying dispersal. Here, we describe primitive amphisbaenians from the North American Palaeocene, including the oldest known amphisbaenian, and provide new and older molecular divergence estimates for the clade, showing that worm lizards originated in North America, then radiated and dispersed in the Palaeogene following the Cretaceous-Palaeogene (K-Pg) extinction. This scenario implies at least three trans-oceanic dispersals: from North America to Europe, from North America to Africa and from Africa to South America. Amphisbaenians provide a striking case study in biogeography, suggesting that the role of continental drift in biogeography may be overstated. Instead, these patterns support Darwin and Wallace's hypothesis that the geographical ranges of modern clades result from dispersal, including oceanic rafting. Mass extinctions may facilitate dispersal events by eliminating competitors and predators that would otherwise hinder establishment of dispersing populations, removing biotic barriers to dispersal. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  8. Adrenalectomy eliminates the extinction spike in autoshaping with rats.

    PubMed

    Thomas, B L; Papini, M R

    2001-03-01

    Experiment 1, using rats, investigated the effect of adrenalectomy (ADX) on the invigoration of lever-contact performance that occurs in the autoshaping situation after a shift from acquisition to extinction (called the extinction spike). Groups of rats with ADX or sham operations were trained under spaced and massed conditions [average intertrial intervals (ITI) of either 15 or 90 s] for 10 sessions and then shifted to extinction. ADX did not affect acquisition training but it eliminated the extinction spike. Plasma corticosterone levels during acquisition were shown in Experiment 2 to be similar in rats trained under spaced or massed conditions. Adrenal participation in the emotional arousal induced by conditions of surprising nonreward (e.g., extinction) is discussed.

  9. Evidence for local and global redox conditions at an Early Ordovician (Tremadocian) mass extinction

    NASA Astrophysics Data System (ADS)

    Edwards, Cole T.; Fike, David A.; Saltzman, Matthew R.; Lu, Wanyi; Lu, Zunli

    2018-01-01

    Profound changes in environmental conditions, particularly atmospheric oxygen levels, are thought to be important drivers of several major biotic events (e.g. mass extinctions and diversifications). The early Paleozoic represents a key interval in the oxygenation of the ocean-atmosphere system and evolution of the biosphere. Global proxies (e.g. carbon (δ13C) and sulfur (δ34S) isotopes) are used to diagnose potential changes in oxygenation and infer causes of environmental change and biotic turnover. The Cambrian-Ordovician contains several trilobite extinctions (some are apparently local, but others are globally correlative) that are attributed to anoxia based on coeval positive δ13C and δ34S excursions. These extinction and excursion events have yet to be coupled with more recently developed proxies thought to be more reflective of local redox conditions in the water column (e.g. I/Ca) to confirm whether these extinctions were associated with oxygen crises over a regional or global scale. Here we examine an Early Ordovician (Tremadocian Stage) extinction event previously interpreted to reflect a continuation of recurrent early Paleozoic anoxic events that expanded into nearshore environments. δ13C, δ34S, and I/Ca trends were measured from three sections in the Great Basin region to test whether I/Ca trends support the notion that anoxia was locally present in the water column along the Laurentian margin. Evidence for anoxia is based on coincident, but not always synchronous, positive δ13C and δ34S excursions (mainly from carbonate-associated sulfate and less so from pyrite data), a 30% extinction of standing generic diversity, and near-zero I/Ca values. Although evidence for local water column anoxia from the I/Ca proxy broadly agrees with intervals of global anoxia inferred from δ13C and δ34S trends, a more complex picture is evident where spatially and temporally variable local trends are superimposed on time-averaged global trends. Stratigraphic

  10. Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction

    NASA Astrophysics Data System (ADS)

    Kaiho, Kunio; Oshima, Naga; Adachi, Kouji; Adachi, Yukimasa; Mizukami, Takuya; Fujibayashi, Megumu; Saito, Ryosuke

    2016-07-01

    The mass extinction of life 66 million years ago at the Cretaceous/Paleogene boundary, marked by the extinctions of dinosaurs and shallow marine organisms, is important because it led to the macroevolution of mammals and appearance of humans. The current hypothesis for the extinction is that an asteroid impact in present-day Mexico formed condensed aerosols in the stratosphere, which caused the cessation of photosynthesis and global near-freezing conditions. Here, we show that the stratospheric aerosols did not induce darkness that resulted in milder cooling than previously thought. We propose a new hypothesis that latitude-dependent climate changes caused by massive stratospheric soot explain the known mortality and survival on land and in oceans at the Cretaceous/Paleogene boundary. The stratospheric soot was ejected from the oil-rich area by the asteroid impact and was spread globally. The soot aerosols caused sufficiently colder climates at mid-high latitudes and drought with milder cooling at low latitudes on land, in addition to causing limited cessation of photosynthesis in global oceans within a few months to two years after the impact, followed by surface-water cooling in global oceans in a few years. The rapid climate change induced terrestrial extinctions followed by marine extinctions over several years.

  11. Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction

    PubMed Central

    Kaiho, Kunio; Oshima, Naga; Adachi, Kouji; Adachi, Yukimasa; Mizukami, Takuya; Fujibayashi, Megumu; Saito, Ryosuke

    2016-01-01

    The mass extinction of life 66 million years ago at the Cretaceous/Paleogene boundary, marked by the extinctions of dinosaurs and shallow marine organisms, is important because it led to the macroevolution of mammals and appearance of humans. The current hypothesis for the extinction is that an asteroid impact in present-day Mexico formed condensed aerosols in the stratosphere, which caused the cessation of photosynthesis and global near-freezing conditions. Here, we show that the stratospheric aerosols did not induce darkness that resulted in milder cooling than previously thought. We propose a new hypothesis that latitude-dependent climate changes caused by massive stratospheric soot explain the known mortality and survival on land and in oceans at the Cretaceous/Paleogene boundary. The stratospheric soot was ejected from the oil-rich area by the asteroid impact and was spread globally. The soot aerosols caused sufficiently colder climates at mid–high latitudes and drought with milder cooling at low latitudes on land, in addition to causing limited cessation of photosynthesis in global oceans within a few months to two years after the impact, followed by surface-water cooling in global oceans in a few years. The rapid climate change induced terrestrial extinctions followed by marine extinctions over several years. PMID:27414998

  12. Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction.

    PubMed

    Kaiho, Kunio; Oshima, Naga; Adachi, Kouji; Adachi, Yukimasa; Mizukami, Takuya; Fujibayashi, Megumu; Saito, Ryosuke

    2016-07-14

    The mass extinction of life 66 million years ago at the Cretaceous/Paleogene boundary, marked by the extinctions of dinosaurs and shallow marine organisms, is important because it led to the macroevolution of mammals and appearance of humans. The current hypothesis for the extinction is that an asteroid impact in present-day Mexico formed condensed aerosols in the stratosphere, which caused the cessation of photosynthesis and global near-freezing conditions. Here, we show that the stratospheric aerosols did not induce darkness that resulted in milder cooling than previously thought. We propose a new hypothesis that latitude-dependent climate changes caused by massive stratospheric soot explain the known mortality and survival on land and in oceans at the Cretaceous/Paleogene boundary. The stratospheric soot was ejected from the oil-rich area by the asteroid impact and was spread globally. The soot aerosols caused sufficiently colder climates at mid-high latitudes and drought with milder cooling at low latitudes on land, in addition to causing limited cessation of photosynthesis in global oceans within a few months to two years after the impact, followed by surface-water cooling in global oceans in a few years. The rapid climate change induced terrestrial extinctions followed by marine extinctions over several years.

  13. Estimating How Often Mass Extinctions Due to Impacts Occur on the Earth

    NASA Technical Reports Server (NTRS)

    Buratti, Bonnie J.

    2013-01-01

    This hands-on, inquiry based activity has been taught at JPL's summer workshop "Teachers Touch the Sky" for the past two decades. Students act as mini-investigators as they gather and analyze data to estimate how often an impact large enough to cause a mass extinction occurs on the Earth. Large craters are counted on the Moon, and this number is extrapolated to the size of the Earth. Given the age of the Solar System, the students can then estimate how often large impacts occur on the Earth. This activity is based on an idea by Dr. David Morrison, NASA Ames Research Center.

  14. Flood basalts and extinction events

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1993-01-01

    The largest known effusive eruptions during the Cenozoic and Mesozoic Eras, the voluminous flood basalts, have long been suspected as being associated with major extinctions of biotic species. Despite the possible errors attached to the dates in both time series of events, the significance level of the suspected correlation is found here to be 1 percent to 4 percent. Statistically, extinctions lag eruptions by a mean time interval that is indistinguishable from zero, being much less than the average residual derived from the correlation analysis. Oceanic flood basalts, however, must have had a different biological impact, which is still uncertain owing to the small number of known examples and differing physical factors. Although not all continental flood basalts can have produced major extinction events, the noncorrelating eruptions may have led to smaller marine extinction events that terminated at least some of the less catastrophically ending geologic stages. Consequently, the 26 Myr quasi-periodicity seen in major marine extinctions may be only a sampling effect, rather than a manifestation of underlying periodicity.

  15. Dust extinction in the first galaxies

    NASA Astrophysics Data System (ADS)

    Jaacks, Jason; Finkelstein, Steven L.; Bromm, Volker

    2018-04-01

    Using cosmological volume simulations and a custom built sub-grid model for Population III (Pop III) star formation, we examine the baseline dust extinction in the first galaxies due to Pop III metal enrichment in the first billion years of cosmic history. We find that although the most enriched, high-density lines of sight in primordial galaxies can experience a measurable amount of extinction from Pop III dust [E(B - V)max = 0.07, AV, max ≈ 0.28], the average extinction is very low with ≲ 10-3. We derive a power-law relationship between dark matter halo mass and extinction of E(B-V)∝ M_halo^{0.80}. Performing a Monte Carlo parameter study, we establish the baseline reddening of the ultraviolet spectra of dwarf galaxies at high redshift due to Pop III enrichment only. With this method, we find <βUV> - 2.51 ± 0.07, which is both nearly halo mass and redshift independent.

  16. Impact as a general cause of extinction: A feasibility test

    NASA Technical Reports Server (NTRS)

    Raup, David M.

    1988-01-01

    Large body impact has been implicated as the possible cause of several extinction events. This is entirely plausible if one accepts two propositions: (1) that impacts of large comets and asteroids produce environmental effects severe enough to cause significant species extinctions and (2) that the estimates of comet and asteroid flux for the Phanerozoic are approximately correct. A resonable next step is to investigate the possibility that impact could be a significant factor in the broader Phanerozoic extinction record, not limited merely to a few events of mass extinction. Monte Carlo simulation experiments based on existing flux estimates and reasonable predictions of the relationship between bolide diameter and extinction are discussed. The simulation results raise the serious possibility that large body impact may be a more pervasive factor in extinction than has been assumed heretofore. At the very least, the experiments show that the comet and asteroid flux estimates combined with a reasonable kill curve produces a reasonable extinction record, complete with occasional mass extinctions and the irregular, lower intensity extinctions commonly called background extinction.

  17. Geography of end-Cretaceous marine bivalve extinctions

    NASA Technical Reports Server (NTRS)

    Raup, David M.; Jablonski, David

    1993-01-01

    Analysis of the end-Cretaceous mass extinction, based on 3514 occurrences of 340 genera of marine bivalves (Mollusca), suggests that extinction intensities were uniformly global; no latitudinal gradients or other geographic patterns are detected. Elevated extinction intensities in some tropical areas are entirely a result of the distribution of one extinct group of highly specialized bivalves, the rudists. When rudists are omitted, intensities at those localities are statistically indistinguishable from those of both the rudist-free tropics and extratropical localities.

  18. Changhsingian conodont succession and the end-Permian mass extinction event at the Daijiagou section in Chongqing, Southwest China

    NASA Astrophysics Data System (ADS)

    Yuan, Dong-xun; Chen, Jun; Zhang, Yi-chun; Zheng, Quan-feng; Shen, Shu-zhong

    2015-06-01

    Previous studies suggested rapid evolution of conodonts across the Permian-Triassic boundary (PTB), and the end-Permian mass extinction pattern varies in different sections in South China. Here we document a high-resolution conodont succession from a carbonate facies of the Changhsingian Stage and across the PTB at the Daijiagou section, about 35 km north to Chongqing City, Southwest China. Two genera and twelve species are identified. Seven conodont zones are recognized from the uppermost part of the Lungtan Formation to the lowest Feixianguan Formation. They are the Clarkina liangshanensis, C. wangi, C. subcarinata, C. changxingensis, C. yini, C. meishanensis, and Hindeodus parvus zones in ascending order. Based on the high-resolution biostratigraphical framework at Daijiagou, the end-Permian mass extinction was rapid and it began in the base of the Clarkina meishanensis Zone. Associated with the extinction, a negative excursion of δ13Ccarb started in the middle part of Clarkina yini Zone with a progressive shift of 1.6‰ to the middle part of the Clarkina meishanensis, followed by a sharp shift of 3.51‰ from the Clarkina meishanensis Zone to the Hindeodus parvus Zone. Our study also suggests that the Triassic index species Hindeodus parvus co-occurred with Hindeodus changxingensis and Clarkina zhejiangensis and directly overlies the Clarkina meishanensis Zone at the Daijiagou section. All these data from the Daijiagou section and some previous studies of other sections in Sichuan, Guizhou provinces and Chongqing City suggest that the first occurrences of Hindeodus parvus are slightly earlier than the sharp negative excursion of δ13Ccarb and the FAD at the Meishan GSSP section. We consider that the slight difference of the end-Permian mass extinction, chemostratigraphy and conodont biostratigraphy at Daijiagou and its adjacent areas is most likely subject to different lithofacies, fossil preservation, and the constraint on the stratigraphic resolution rather

  19. Historical and contingent factors affect re-evolution of a complex feature lost during mass extinction in communities of digital organisms.

    PubMed

    Yedid, G; Ofria, C A; Lenski, R E

    2008-09-01

    Re-evolution of complex biological features following the extinction of taxa bearing them remains one of evolution's most interesting phenomena, but is not amenable to study in fossil taxa. We used communities of digital organisms (computer programs that self-replicate, mutate and evolve), subjected to periods of low resource availability, to study the evolution, loss and re-evolution of a complex computational trait, the function EQU (bit-wise logical equals). We focused our analysis on cases where the pre-extinction EQU clade had surviving descendents at the end of the extinction episode. To see if these clades retained the capacity to re-evolve EQU, we seeded one set of multiple subreplicate 'replay' populations using the most abundant survivor of the pre-extinction EQU clade, and another set with the actual end-extinction ancestor of the organism in which EQU re-evolved following the extinction episode. Our results demonstrate that stochastic, historical, genomic and ecological factors can lead to constraints on further adaptation, and facilitate or hinder re-evolution of a complex feature.

  20. Star counts and visual extinctions in dark nebulae

    NASA Technical Reports Server (NTRS)

    Dickman, R. L.

    1978-01-01

    Application of star count techniques to the determination of visual extinctions in compact, fairly high-extinction dark nebulae is discussed. Particular attention is devoted to the determination of visual extinctions for a cloud having a possibly anomalous ratio of total to selective extinction. The techniques discussed are illustrated in application at two colors to four well-known compact dust clouds or Bok globules: Barnard 92, B 133, B 134, and B 335. Minimum masses and lower limits to the central extinction of these objects are presented.

  1. Extinction of Harrington's mountain goat

    PubMed Central

    Mead, Jim I.; Martin, Paul S.; Euler, Robert C.; Long, Austin; Jull, A. J. T.; Toolin, Laurence J.; Donahue, Douglas J.; Linick, T. W.

    1986-01-01

    Keratinous horn sheaths of the extinct Harrington's mountain goat, Oreamnos harringtoni, were recovered at or near the surface of dry caves of the Grand Canyon, Arizona. Twenty-three separate specimens from two caves were dated nondestructively by the tandem accelerator mass spectrometer (TAMS). Both the TAMS and the conventional dates indicate that Harrington's mountain goat occupied the Grand Canyon for at least 19,000 years prior to becoming extinct by 11,160 ± 125 radiocarbon years before present. The youngest average radiocarbon dates on Shasta ground sloths, Nothrotheriops shastensis, from the region are not significantly younger than those on extinct mountain goats. Rather than sequential extinction with Harrington's mountain goat disappearing from the Grand Canyon before the ground sloths, as one might predict in view of evidence of climatic warming at the time, the losses were concurrent. Both extinctions coincide with the regional arrival of Clovis hunters. Images PMID:16593655

  2. Mass extinctions caused by large bolide impacts

    SciTech Connect

    Alvarez, L.W.

    1987-07-01

    Evidence indicates that the collision of Earth and a large piece of Solar System derbris such as a meteoroid, asteroid or comet caused the great extinctions of 65 million years ago, leading to the transition from the age of the dinosaurs to the age of the mammals.

  3. Recovery after mass extinction: evolutionary assembly in large-scale biosphere dynamics.

    PubMed Central

    Solé, Ricard V; Montoya, José M; Erwin, Douglas H

    2002-01-01

    Biotic recoveries following mass extinctions are characterized by a process in which whole ecologies are reconstructed from low-diversity systems, often characterized by opportunistic groups. The recovery process provides an unexpected window to ecosystem dynamics. In many aspects, recovery is very similar to ecological succession, but important differences are also apparently linked to the innovative patterns of niche construction observed in the fossil record. In this paper, we analyse the similarities and differences between ecological succession and evolutionary recovery to provide a preliminary ecological theory of recoveries. A simple evolutionary model with three trophic levels is presented, and its properties (closely resembling those observed in the fossil record) are compared with characteristic patterns of ecological response to disturbances in continuous models of three-level ecosystems. PMID:12079530

  4. The silent mass extinction of insect herbivores in biodiversity hotspots.

    PubMed

    Fonseca, Carlos Roberto

    2009-12-01

    Habitat loss is silently leading numerous insects to extinction. Conservation efforts, however, have not been designed specifically to protect these organisms, despite their ecological and evolutionary significance. On the basis of species-host area equations, parameterized with data from the literature and interviews with botanical experts, I estimated the number of specialized plant-feeding insects (i.e., monophages) that live in 34 biodiversity hotspots and the number committed to extinction because of habitat loss. I estimated that 795,971-1,602,423 monophagous insect species live in biodiversity hotspots on 150,371 endemic plant species, which is 5.3-10.6 monophages per plant species. I calculated that 213,830-547,500 monophagous species are committed to extinction in biodiversity hotspots because of reduction of the geographic range size of their endemic hosts. I provided rankings of biodiversity hotspots on the basis of estimated richness of monophagous insects and on estimated number of extinctions of monophagous species. Extinction rates were predicted to be higher in biodiversity hotspots located along strong environmental gradients and on archipelagos, where high spatial turnover of monophagous species along the geographic distribution of their endemic plants is likely. The results strongly support the overall strategy of selecting priority conservation areas worldwide primarily on the basis of richness of endemic plants. To face the global decline of insect herbivores, one must expand the coverage of the network of protected areas and improve the richness of native plants on private lands.

  5. Recovery collapse coincident with ongoing carbon cycle perturbations following the Permian-Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Petsios, E.; Bottjer, D. J.

    2016-12-01

    The Permian-Triassic mass extinction, the largest extinction of the Phanerozoic, is attributed to volcanic outgassing from the Siberian Traps and the resulting climate change. Ongoing volcanism in the Early Triassic is implicated for continued carbon cycle instability following the initial event, reflected in large inorganic carbon isotope excursions throughout the 5 Mya interval. Recent paleoecological studies have shown that timing of recovery from the extinction in the Early Triassic is highly complex, differing between regions, with documented cases of "early" recovery in some environments. The importance of specific environmental factors, such as oxygen levels and sea surface temperatures, in aiding or hindering recovery following the extinction is the topic of ongoing study. Here we present an ecological survey of marine benthic communities from the Lower Triassic Blacktail Creek outcrop of the Dinwoody Formation, correlated bed-for-bed with inorganic carbon isotope values. We observe incipient recovery as communities show increasing richness and evenness throughout the section, followed by a `collapse' with a return of high dominance, low richness fauna coincident with large δ13Ccarb shifts. We observe a statistically significant correlation between the magnitude of δ13Ccarb excursions and benthic community complexity over a stratigraphic section, implying a shared causal mechanism acting at the local scale. The globally correlatable nature of these observed carbon isotope shifts, as well as an absence of lithologic evidence for oxygen limitation, points to thermal stress brought on by pulses of volcanism as the shared cause between recovery collapse and carbon cycle perturbations. We propose that the "early" recovery at Blacktail Creek was truncated by recurrent greenhouse gas induced thermal spikes, highlighting the interplay of local and global environmental conditions in expediting or hindering Early Triassic recovery.

  6. Observations of particle extinction, PM2.5 mass concentration profile and flux in north China based on mobile lidar technique

    NASA Astrophysics Data System (ADS)

    Lv, Lihui; Liu, Wenqing; Zhang, Tianshu; Chen, Zhenyi; Dong, Yunsheng; Fan, Guangqiang; Xiang, Yan; Yao, Yawei; Yang, Nan; Chu, Baolin; Teng, Man; Shu, Xiaowen

    2017-09-01

    Fine particle with diameter <2.5 μm (PM2.5) have important direct and indirect effects on human life and activities. However, the studies of fine particle were limited by the lack of monitoring data obtained with multiple fixed site sampling strategies. Mobile monitoring has provided a means for broad measurement of fine particles. In this research, the potential use of mobile lidar to map the distribution and transport of fine particles was discussed. The spatial and temporal distributions of particle extinction, PM2.5 mass concentration and regional transport flux of fine particle in the planetary boundary layer were investigated with the use of vehicle-based mobile lidar and wind field data from north China. Case studies under different pollution levels in Beijing were presented to evaluate the contribution of regional transport. A vehicle-based mobile lidar system was used to obtain the spatial and temporal distributions of particle extinction in the measurement route. Fixed point lidar and a particulate matter sampler were operated next to each other at the University of Chinese Academy of Science (UCAS) in Beijing to determine the relationship between the particle extinction coefficient and PM2.5 mass concentration. The correlation coefficient (R2) between the particle extinction coefficient and PM2.5 mass concentration was found to be over 0.8 when relative humidity (RH) was less than 90%. A mesoscale meteorological model, the Weather Research and Forecasting (WRF) model, was used to obtain profiles of the horizontal wind speed, wind direction and relative humidity. A vehicle-based mobile lidar technique was applied to estimate transport flux based on the PM2.5 profile and vertical profile of wind data. This method was applicable when hygroscopic growth can be neglected (relatively humidity<90%). Southwest was found to be the main pathway of Beijing during the experiments.

  7. Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary

    PubMed Central

    Martill, David M.; Andres, Brian

    2018-01-01

    Pterosaurs were the first vertebrates to evolve powered flight and the largest animals to ever take wing. The pterosaurs persisted for over 150 million years before disappearing at the end of the Cretaceous, but the patterns of and processes driving their extinction remain unclear. Only a single family, Azhdarchidae, is definitively known from the late Maastrichtian, suggesting a gradual decline in diversity in the Late Cretaceous, with the Cretaceous–Paleogene (K-Pg) extinction eliminating a few late-surviving species. However, this apparent pattern may simply reflect poor sampling of fossils. Here, we describe a diverse pterosaur assemblage from the late Maastrichtian of Morocco that includes not only Azhdarchidae but the youngest known Pteranodontidae and Nyctosauridae. With 3 families and at least 7 species present, the assemblage represents the most diverse known Late Cretaceous pterosaur assemblage and dramatically increases the diversity of Maastrichtian pterosaurs. At least 3 families—Pteranodontidae, Nyctosauridae, and Azhdarchidae—persisted into the late Maastrichtian. Late Maastrichtian pterosaurs show increased niche occupation relative to earlier, Santonian-Campanian faunas and successfully outcompeted birds at large sizes. These patterns suggest an abrupt mass extinction of pterosaurs at the K-Pg boundary. PMID:29534059

  8. The Complex Refractive Index of Volcanic Ash Aerosol Retrieved From Spectral Mass Extinction

    NASA Astrophysics Data System (ADS)

    Reed, Benjamin E.; Peters, Daniel M.; McPheat, Robert; Grainger, R. G.

    2018-01-01

    The complex refractive indices of eight volcanic ash samples, chosen to have a representative range of SiO2 contents, were retrieved from simultaneous measurements of their spectral mass extinction coefficient and size distribution. The mass extinction coefficients, at 0.33-19 μm, were measured using two optical systems: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter; values for the effective radius of ash particles measured in this study varied from 0.574 to 1.16 μm. Verification retrievals on high-purity silica aerosol demonstrated that the Rayleigh continuous distribution of ellipsoids (CDEs) scattering model significantly outperformed Mie theory in retrieving the complex refractive index, when compared to literature values. Assuming the silica particles provided a good analogue of volcanic ash, the CDE scattering model was applied to retrieve the complex refractive index of the eight ash samples. The Lorentz formulation of the complex refractive index was used within the retrievals as a convenient way to ensure consistency with the Kramers-Kronig relation. The short-wavelength limit of the electric susceptibility was constrained by using independently measured reference values of the complex refractive index of the ash samples at a visible wavelength. The retrieved values of the complex refractive indices of the ash samples showed considerable variation, highlighting the importance of using accurate refractive index data in ash cloud radiative transfer models.

  9. Redox conditions and marine microbial community changes during the end-Ordovician mass extinction event

    NASA Astrophysics Data System (ADS)

    Smolarek, Justyna; Marynowski, Leszek; Trela, Wiesław; Kujawski, Piotr; Simoneit, Bernd R. T.

    2017-02-01

    The end-Ordovician (Hirnantian) crisis is the first globally distinct extinction during the Phanerozoic, but its causes are still not fully known. Here, we present an integrated geochemical and petrographic analysis to understand the sedimentary conditions taking place before, during and after the Late Ordovician ice age. New data from the Zbrza (Holy Cross Mountains) and Gołdap (Baltic Depression) boreholes shows that, like in other worldwide sections, the total organic carbon (TOC) content is elevated in the upper Katian and uppermost Hirnantian to Rhudannian black shales, but depleted (below 1%) during most of the Hirnantian. Euxinic conditions occurred in the photic zone in both TOC-rich intervals. This is based on the maleimide distribution, occurrence of aryl isoprenoids and isorenieratane, as well as a dominance of tiny pyrite framboids. Euxinic conditions were interrupted by the Hirnantian regression caused by glaciation. Sedimentation on the deep shelf changed to aerobic probably due to intense thermohaline circulation. Euxinia in the water column occurred directly during the time associated with the second pulse of the mass extinction with a termination of the end-Ordovician glaciation and sea level rise just at the Ordovician/Silurian (O/S) boundary. In contrast, we suggest based on inorganic proxies that bottom water conditions were generally oxic to dysoxic due to upwelling in the Rheic Ocean. The only episode of seafloor anoxia in the Zbrza basin was found at the O/S boundary, where all inorganic indicators showed elevated values typical for anoxia (U/Th > 1.25; V/Cr > 4.25; V/(V + Ni): 0.54-0.82 and Mo > 10-25 ppm). Significant differences in hopanes to steranes ratio and in C27-C29 sterane distribution between the Katian, Rhudannian and Hirnantian deposits indicate changes in marine microbial communities triggered by sharp climate change and Gondwana glaciation. The increase from biomarkers of cyanobacteria (2α-methylhopanes) after the O

  10. Astrophysical implications of periodicity

    NASA Technical Reports Server (NTRS)

    Muller, Richard A.

    1988-01-01

    Two remarkable discoveries of the last decade have profound implications for astrophysics and for geophysics. These are the discovery by Alvarez et al., that certain mass extinctions are caused by the impact on the earth of a large asteroid or comet, and the discovery by Raup and Sepkoski that such extinctions are periodic, with a cycle time of 26 to 30 million years. The validity of both of these discoveries is assumed and the implications are examined. Most of the phenomena described depend not on periodicity, but just on the weaker assumption that the impacts on the earth take place primarily in showers. Proposed explanations for the periodicity include galactic oscillations, the Planet X model, and the possibility of Nemesis, a solar companion star. These hypotheses are critically examined. Results of the search for the solar companion are reported. The Deccan flood basalts of India have been proposed as the impact site for the Cretaceous impact, but this hypotheisis is in contradiction with the conclusion of Courtillot et al., that the magma flow began during a period of normal magnetic field. A possible resolution of this contradiction is proposed.

  11. Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction.

    PubMed

    Field, Daniel J; Bercovici, Antoine; Berv, Jacob S; Dunn, Regan; Fastovsky, David E; Lyson, Tyler R; Vajda, Vivi; Gauthier, Jacques A

    2018-06-04

    The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous-Paleogene (K-Pg) mass extinction [1-3]. However, questions remain regarding the mechanisms underlying the survival of the deepest lineages within crown birds across the K-Pg boundary, particularly since this global catastrophe eliminated even the closest stem-group relatives of Neornithes [4]. Here, ancestral state reconstructions of neornithine ecology reveal a strong bias toward taxa exhibiting predominantly non-arboreal lifestyles across the K-Pg, with multiple convergent transitions toward predominantly arboreal ecologies later in the Paleocene and Eocene. By contrast, ecomorphological inferences indicate predominantly arboreal lifestyles among enantiornithines, the most diverse and widespread Mesozoic avialans [5-7]. Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests [8, 9]. We suggest that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs (Avialae [10]) committed to arboreal ecologies, resulting in a predominantly non-arboreal post-extinction neornithine avifauna composed of total-clade Palaeognathae, Galloanserae, and terrestrial total-clade Neoaves that rapidly diversified into the broad range of avian ecologies familiar today. The explanation proposed here provides a unifying hypothesis for the K-Pg-associated mass extinction of arboreal stem birds, as well as for the post-K-Pg radiation of arboreal crown birds. It also provides a baseline hypothesis to be further refined pending the discovery of additional neornithine fossils from the Latest Cretaceous and earliest Paleogene. Copyright © 2018 Elsevier Ltd. All rights reserved.

  12. The ghosts of mammals past: biological and geographical patterns of global mammalian extinction across the Holocene.

    PubMed

    Turvey, Samuel T; Fritz, Susanne A

    2011-09-12

    Although the recent historical period is usually treated as a temporal base-line for understanding patterns of mammal extinction, mammalian biodiversity loss has also taken place throughout the Late Quaternary. We explore the spatial, taxonomic and phylogenetic patterns of 241 mammal species extinctions known to have occurred during the Holocene up to the present day. To assess whether our understanding of mammalian threat processes has been affected by excluding these taxa, we incorporate extinct species data into analyses of the impact of body mass on extinction risk. We find that Holocene extinctions have been phylogenetically and spatially concentrated in specific taxa and geographical regions, which are often not congruent with those disproportionately at risk today. Large-bodied mammals have also been more extinction-prone in most geographical regions across the Holocene. Our data support the extinction filter hypothesis, whereby regional faunas from which susceptible species have already become extinct now appear less threatened; they may also suggest that different processes are responsible for driving past and present extinctions. We also find overall incompleteness and inter-regional biases in extinction data from the recent fossil record. Although direct use of fossil data in future projections of extinction risk is therefore not straightforward, insights into extinction processes from the Holocene record are still useful in understanding mammalian threat.

  13. The ghosts of mammals past: biological and geographical patterns of global mammalian extinction across the Holocene

    PubMed Central

    Turvey, Samuel T.; Fritz, Susanne A.

    2011-01-01

    Although the recent historical period is usually treated as a temporal base-line for understanding patterns of mammal extinction, mammalian biodiversity loss has also taken place throughout the Late Quaternary. We explore the spatial, taxonomic and phylogenetic patterns of 241 mammal species extinctions known to have occurred during the Holocene up to the present day. To assess whether our understanding of mammalian threat processes has been affected by excluding these taxa, we incorporate extinct species data into analyses of the impact of body mass on extinction risk. We find that Holocene extinctions have been phylogenetically and spatially concentrated in specific taxa and geographical regions, which are often not congruent with those disproportionately at risk today. Large-bodied mammals have also been more extinction-prone in most geographical regions across the Holocene. Our data support the extinction filter hypothesis, whereby regional faunas from which susceptible species have already become extinct now appear less threatened; they may also suggest that different processes are responsible for driving past and present extinctions. We also find overall incompleteness and inter-regional biases in extinction data from the recent fossil record. Although direct use of fossil data in future projections of extinction risk is therefore not straightforward, insights into extinction processes from the Holocene record are still useful in understanding mammalian threat. PMID:21807737

  14. Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction.

    PubMed

    Zhang, Feifei; Romaniello, Stephen J; Algeo, Thomas J; Lau, Kimberly V; Clapham, Matthew E; Richoz, Sylvain; Herrmann, Achim D; Smith, Harrison; Horacek, Micha; Anbar, Ariel D

    2018-04-01

    Explaining the ~5-million-year delay in marine biotic recovery following the latest Permian mass extinction, the largest biotic crisis of the Phanerozoic, is a fundamental challenge for both geological and biological sciences. Ocean redox perturbations may have played a critical role in this delayed recovery. However, the lack of quantitative constraints on the details of Early Triassic oceanic anoxia (for example, time, duration, and extent) leaves the links between oceanic conditions and the delayed biotic recovery ambiguous. We report high-resolution U-isotope (δ 238 U) data from carbonates of the uppermost Permian to lowermost Middle Triassic Zal section (Iran) to characterize the timing and global extent of ocean redox variation during the Early Triassic. Our δ 238 U record reveals multiple negative shifts during the Early Triassic. Isotope mass-balance modeling suggests that the global area of anoxic seafloor expanded substantially in the Early Triassic, peaking during the latest Permian to mid-Griesbachian, the late Griesbachian to mid-Dienerian, the Smithian-Spathian transition, and the Early/Middle Triassic transition. Comparisons of the U-, C-, and Sr-isotope records with a modeled seawater PO 4 3- concentration curve for the Early Triassic suggest that elevated marine productivity and enhanced oceanic stratification were likely the immediate causes of expanded oceanic anoxia. The patterns of redox variation documented by the U-isotope record show a good first-order correspondence to peaks in ammonoid extinctions during the Early Triassic. Our results indicate that multiple oscillations in oceanic anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction.

  15. Geochemical and palynological records for the end-Triassic Mass-Extinction Event in the NE Paris Basin (Luxemburg)

    NASA Astrophysics Data System (ADS)

    Kuhlmann, Natascha; van de Schootbrugge, Bas; Thein, Jean; Fiebig, Jens; Franz, Sven-Oliver; Hanzo, Micheline; Colbach, Robert; Faber, Alain

    2016-04-01

    The End-Triassic mass-extinction event is one of the "big five" mass extinctions in Earth's history. Large scale flood basalt volcanism associated with the break-up of Pangaea, which resulted in the opening of the central Atlantic Ocean, is considered as the leading cause. In addition, an asteroid impact in Rochechouart (France; 201 ± 2 Ma) may have had a local influence on ecosystems and sedimentary settings. The Luxembourg Embayment, in the NE Paris Basin, offers a rare chance to study both effects in a range of settings from deltaic to lagoonal. A multidisciplinary study (sedimentology, geochemistry, palynology) has been carried out on a number of outcrops and cores that span from the Norian to lower Hettangian. Combined geochemical and palynological records from the Boust core drilled in the NE Paris Basin, provide evidence for paleoenvironmental changes associated with the end-Triassic mass-extinction event. The Triassic-Jurassic stratigraphy of the Boust core is well constrained by palynomorphs showing the disappaerance of typical Triassic pollen taxa (e.g. Ricciisporites tuberculates) and the occurrence of the marker species Polypodiisporites polymicroforatus within the uppermost Rhaetian, prior to the Hettangian dominance of Classopollis pollen. The organic carbon stable isotope record (δ13Corg) spanning the Norian to Hettangian, shows a series of prominent negative excursions within the middle Rhaetian, followed by a trend towards more positive values (approx -24 per mille) within the uppermost Rhaetian Argiles de Levallois Member. The lowermost Hettangian is characterized by a major negative excursion, reaching - 30 per mille that occurs in organic-rich sediments. This so-called "main negative excursion" is well-known from other locations, for example from Mariental in Northern Germany and from St Audrie's Bay in England, and Stenlille in Denmark. Based on redox-sensitive trace element records (V, Cr, Ni, Co, Th, U) the lowermost Hettangian in most of

  16. The fossil record of evolution: Data on diversification and extinction

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J., Jr.

    1991-01-01

    Understanding of the evolution of complex life, and of the roles that changing terrestrial and extraterrestrial environments played in life's history, is dependent upon synthetic knowledge of the fossil record. Paleontologists have been describing fossils for more that two centuries. However, much of this information is dispersed in monographs and journal articles published throughout the world. Over the past several years, this literature was surveyed, and a data base on times of origination and extinction of fossil genera was compiled. The data base, which now holds approximately 32,000 genera, covers all taxonomic groups of marine animals, incorporates the most recent taxonomic assignments, and uses a detailed global time framework that can resolve originations and extinctions to intervals averaging three million years in duration. These data can be used to compile patterns of global biodiversity, measure rates of taxic evolution, and test hypotheses concerning adaptive radiations, mass extinctions, etc. Thus far, considerable effort was devoted to using the data to test the hypothesis of periodicity of mass extinction. Rates of extinction measured from the data base have also been used to calibrate models of evolutionary radiations in marine environments. It was observed that new groups, or clades of animals (i.e., orders and classes) tend to reach appreciable diversity first in nearshore environments and then to radiate in more offshore environments; during decline, these clades may disappear from the nearshore while persisting in offshore, deep water habitats. These observations have led to suggestions that there is something special about stressful or perturbed environments that promotes the evolution of novel kinds of animals that can rapidly replace their predecessors. The numerical model that is being investigated to study this phenomenon treats environments along onshore-offshore gradients as if they were discrete habitats. Other aspects of this

  17. Mapping of the extinction in giant molecular clouds using optical star counts

    NASA Astrophysics Data System (ADS)

    Cambrésy, L.

    1999-05-01

    This paper presents large scale extinction maps of most nearby Giant Molecular Clouds of the Galaxy (Lupus, rho Ophiuchus, Scorpius, Coalsack, Taurus, Chamaeleon, Musca, Corona Australis, Serpens, IC 5146, Vela, Orion, Monoceros R1 and R2, Rosette, Carina) derived from a star count method using an adaptive grid and a wavelet decomposition applied to the optical data provided by the USNO-Precision Measuring Machine. The distribution of the extinction in the clouds leads to estimate their total individual masses M and their maximum of extinction. I show that the relation between the mass contained within an iso-extinction contour and the extinction is similar from cloud to cloud and allows the extrapolation of the maximum of extinction in the range 5.7 to 25.5 magnitudes. I found that about half of the mass is contained in regions where the visual extinction is smaller than 1 magnitude. The star count method used on large scale ( ~ 250 square degrees) is a powerful and relatively straightforward method to estimate the mass of molecular complexes. A systematic study of the all sky would lead to discover new clouds as I did in the Lupus complex for which I found a sixth cloud of about 10(4) M_⊙.

  18. Sources of variation in extinction rates, turnover, and diversity of marine invertebrate families during the Paleozoic

    USGS Publications Warehouse

    Nichols, J.D.; Morris, R.W.; Brownie, C.; Pollock, K.H.

    1986-01-01

    The authors present a new method that can be used to estimate taxonomic turnover in conjunction with stratigraphic range data for families in five phyla of Paleozoic marine invertebrates. Encounter probabilities varied among taxa and showed evidence of a decrease over time for the geologic series examined. The number of families varied substantially among the five phyla and showed some evidence of an increase over the series examined. There was no evidence of variation in extinction probabilities among the phyla. Although there was evidence of temporal variation in extinction probabilities within phyla, there was no evidence of a linear decrease in extinction probabilities over time, as has been reported by others. The authors did find evidence of high extinction probabilities for the two intervals that had been identified by others as periods of mass extinction. They found no evidence of variation in turnover among the five phyla. There was evidence of temporal variation in turnover, with greater turnover occurring in the older series.

  19. Elevated Extinction Rates as a Trigger for Diversification Rate Shifts: Early Amniotes as a Case Study

    PubMed Central

    Brocklehurst, Neil; Ruta, Marcello; Müller, Johannes; Fröbisch, Jörg

    2015-01-01

    Tree shape analyses are frequently used to infer the location of shifts in diversification rate within the Tree of Life. Many studies have supported a causal relationship between shifts and temporally coincident events such as the evolution of “key innovations”. However, the evidence for such relationships is circumstantial. We investigated patterns of diversification during the early evolution of Amniota from the Carboniferous to the Triassic, subjecting a new supertree to analyses of tree balance in order to infer the timing and location of diversification shifts. We investigated how uneven origination and extinction rates drive diversification shifts, and use two case studies (herbivory and an aquatic lifestyle) to examine whether shifts tend to be contemporaneous with evolutionary novelties. Shifts within amniotes tend to occur during periods of elevated extinction, with mass extinctions coinciding with numerous and larger shifts. Diversification shifts occurring in clades that possess evolutionary innovations do not coincide temporally with the appearance of those innovations, but are instead deferred to periods of high extinction rate. We suggest such innovations did not cause increases in the rate of cladogenesis, but allowed clades to survive extinction events. We highlight the importance of examining general patterns of diversification before interpreting specific shifts. PMID:26592209

  20. Ca and Sr isotope records support ocean acidification during end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Wang, J.; Jacobson, A. D.; Zhang, H.; Ramezani, J.; Sageman, B. B.; Hurtgen, M.; Bowring, S. A.; Shen, S.

    2017-12-01

    The end-Permian mass extinction represents the most devastating loss of biodiversity during the Phanerozoic. A negative carbon isotope (δ13C) excursion that accompanies the event suggests a significant perturbation to the global carbon cycle, likely induced by CO2 emissions during eruption of the Siberian Traps large igneous province. The carbon cycle is linked with the Ca and Sr cycles through chemical weathering and carbonate precipitation. Therefore, analyses of Ca (δ44/40Ca), radiogenic Sr (87Sr/86Sr), and stable Sr (δ88/86Sr) isotope abundance variations in marine carbonate rocks spanning the Permian-Triassic Boundary (PTB) can reveal key information about biogeochemical changes that occurred during this time. We report δ44/40Ca, 87Sr/86Sr, and δ88/86Sr records analyzed by TIMS for the Meishan and Dajiang sections in China. δ44/40Ca values exhibit similar patterns in both sections. The values remain unchanged across the extinction event layer (EXT) and then decrease by 0.20‰ before increasing by 0.20‰ to 0.40‰ around the PTB. In the Meishan section, 87Sr/86Sr ratios increase after the EXT and return to pre-excursion levels by the PTB. Simultaneously, δ88/86Sr values decrease by 0.12‰ across the EXT and increase by 0.08‰ by the PTB. The patterns of our data support the hypothesis that elevated atmospheric CO2 levels enhanced chemical weathering inputs and might have caused transient ocean acidification, with an "alkalinity overshoot" and increased carbonate deposition occurring after the extinction. Additional measurements and model calculations are underway to help refine and improve these preliminary interpretations.

  1. The role of extinction in evolution

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1994-01-01

    The extinction of species is not normally considered an important element of neodarwinian theory, in contrast to the opposite phenomenon, speciation. This is surprising in view of the special importance Darwin attached to extinction, and because the number of species extinctions in the history of life is almost the same as the number of originations; present-day biodiversity is the result of a trivial surplus of originations, cumulated over millions of years. For an evolutionary biologist to ignore extinction is probably as foolhardy as for a demographer to ignore mortality. The past decade has seen a resurgence of interest in extinction, yet research on the topic is still at a reconnaissance level, and our present understanding of its role in evolution is weak. Despite uncertainties, extinction probably contains three important elements. (i) For geographically widespread species, extinction is likely only if the killing stress is one so rare as to be beyond the experience of the species, and thus outside the reach of natural selection. (ii) The largest mass extinctions produce major restructuring of the biosphere wherein some successful groups are eliminated, allowing previously minor groups to expand and diversify. (iii) Except for a few cases, there is little evidence that extinction is selective in the positive sense argued by Darwin. It has generally been impossible to predict, before the fact, which species will be victims of an extinction event.

  2. PM2.5 mass, chemical composition, and light extinction before and during the 2008 Beijing Olympics

    NASA Astrophysics Data System (ADS)

    Li, Xinghua; He, Kebin; Li, Chengcai; Yang, Fumo; Zhao, Qing; Ma, Yongliang; Cheng, Yuan; Ouyang, Wenjuan; Chen, Gangcai

    2013-11-01

    contrast of air quality and visibility before and during the 2008 Beijing Olympic Games provides a rare opportunity to investigate the links between PM2.5 mass, chemical composition, and light extinction in this megacity. Twenty-four hour integrated PM2.5 samples were collected, and light scattering coefficients and the concentrations of black carbon were measured at urban Beijing for this purpose during a measurement campaign from 1 July to 20 September 2008, which was classed into four stages according to the levels of emission control measures. Daily PM2.5 concentrations ranged from 15.9 to 156.7 µg m-3 with an average of 66.0 ± 35.1 µg m-3. The average PM2.5 mass during the Olympics decreased by 49% from the second stage (20 July to 7 August), mainly due to the reduction of secondary inorganic aerosols (i.e., sulfate, nitrate, and ammonium (SNA)). The counterintuitive increase of PM2.5 mass (by 27% on average) during the second stage with two most serious haze episodes, although more rigorous emission control measures were in place, compared to the first stage (1-19 July), was mainly explained by the unfavorable meteorology and input of sulfate aerosols. A daily PM2.5 mass threshold of 50 µg m-3 was extracted for frequent haze occurrence. The extinction fractions of SNA and organic material were each approximately 30% during the 20% best visibility days but changed to 81.7% and 8.4%, respectively, during the 20% worst visibility days. The results indicated that the role of SNA was magnified in haze formation during the 2008 summer in Beijing.

  3. Subsequent biotic crises delayed marine recovery following the late Permian mass extinction event in northern Italy

    PubMed Central

    Danise, Silvia; Price, Gregory D.; Twitchett, Richard J.

    2017-01-01

    The late Permian mass extinction event was the largest biotic crisis of the Phanerozoic and has the longest recovery interval of any extinction event. It has been hypothesised that subsequent carbon isotope perturbations during the Early Triassic are associated with biotic crises that impeded benthic recovery. We test this hypothesis by undertaking the highest-resolution study yet made of the rock and fossil records of the entire Werfen Formation, Italy. Here, we show that elevated extinction rates were recorded not only in the Dienerian, as previously recognised, but also around the Smithian/Spathian boundary. Functional richness increases across the Smithian/Spathian boundary associated with elevated origination rates in the lower Spathian. The taxonomic and functional composition of benthic faunas only recorded two significant changes: (1) reduced heterogeneity in the Dienerian, and (2) and a faunal turnover across the Smithian/Spathian boundary. The elevated extinctions and compositional shifts in the Dienerian and across the Smithian/Spathian boundary are associated with a negative and positive isotope excursion, respectively, which supports the hypothesis that subsequent biotic crises are associated with carbon isotope shifts. The Spathian fauna represents a more advanced ecological state, not recognised in the previous members of the Werfen Formation, with increased habitat differentiation, a shift in the dominant modes of life, appearance of stenohaline taxa and the occupation of the erect and infaunal tiers. In addition to subsequent biotic crises delaying the recovery, therefore, persistent environmental stress limited the ecological complexity of benthic recovery prior to the Spathian. PMID:28296886

  4. Progress to extinction: increased specialisation causes the demise of animal clades.

    PubMed

    Raia, P; Carotenuto, F; Mondanaro, A; Castiglione, S; Passaro, F; Saggese, F; Melchionna, M; Serio, C; Alessio, L; Silvestro, D; Fortelius, M

    2016-08-10

    Animal clades tend to follow a predictable path of waxing and waning during their existence, regardless of their total species richness or geographic coverage. Clades begin small and undifferentiated, then expand to a peak in diversity and range, only to shift into a rarely broken decline towards extinction. While this trajectory is now well documented and broadly recognised, the reasons underlying it remain obscure. In particular, it is unknown why clade extinction is universal and occurs with such surprising regularity. Current explanations for paleontological extinctions call on the growing costs of biological interactions, geological accidents, evolutionary traps, and mass extinctions. While these are effective causes of extinction, they mainly apply to species, not clades. Although mass extinctions is the undeniable cause for the demise of a sizeable number of major taxa, we show here that clades escaping them go extinct because of the widespread tendency of evolution to produce increasingly specialised, sympatric, and geographically restricted species over time.

  5. Progress to extinction: increased specialisation causes the demise of animal clades

    NASA Astrophysics Data System (ADS)

    Raia, P.; Carotenuto, F.; Mondanaro, A.; Castiglione, S.; Passaro, F.; Saggese, F.; Melchionna, M.; Serio, C.; Alessio, L.; Silvestro, D.; Fortelius, M.

    2016-08-01

    Animal clades tend to follow a predictable path of waxing and waning during their existence, regardless of their total species richness or geographic coverage. Clades begin small and undifferentiated, then expand to a peak in diversity and range, only to shift into a rarely broken decline towards extinction. While this trajectory is now well documented and broadly recognised, the reasons underlying it remain obscure. In particular, it is unknown why clade extinction is universal and occurs with such surprising regularity. Current explanations for paleontological extinctions call on the growing costs of biological interactions, geological accidents, evolutionary traps, and mass extinctions. While these are effective causes of extinction, they mainly apply to species, not clades. Although mass extinctions is the undeniable cause for the demise of a sizeable number of major taxa, we show here that clades escaping them go extinct because of the widespread tendency of evolution to produce increasingly specialised, sympatric, and geographically restricted species over time.

  6. Mass extinction in tetraodontiform fishes linked to the Palaeocene-Eocene thermal maximum.

    PubMed

    Arcila, Dahiana; Tyler, James C

    2017-11-15

    Integrative evolutionary analyses based upon fossil and extant species provide a powerful approach for understanding past diversification events and for assessing the tempo of evolution across the Tree of Life. Herein, we demonstrate the importance of integrating fossil and extant species for inferring patterns of lineage diversification that would otherwise be masked in analyses that examine only one source of evidence. We infer the phylogeny and macroevolutionary history of the Tetraodontiformes (triggerfishes, pufferfishes and allies), a group with one of the most extensive fossil records among fishes. Our analyses combine molecular and morphological data, based on an expanded matrix that adds newly coded fossil species and character states. Beyond confidently resolving the relationships and divergence times of tetraodontiforms, our diversification analyses detect a major mass-extinction event during the Palaeocene-Eocene Thermal Maximum (PETM), followed by a marked increase in speciation rates. This pattern is consistently obtained when fossil and extant species are integrated, whereas examination of the fossil occurrences alone failed to detect major diversification changes during the PETM. When taking into account non-homogeneous models, our analyses also detect a rapid lineage diversification increase in one of the groups (tetraodontoids) during the middle Miocene, which is considered a key period in the evolution of reef fishes associated with trophic changes and ecological opportunity. In summary, our analyses show distinct diversification dynamics estimated from phylogenies and the fossil record, suggesting that different episodes shaped the evolution of tetraodontiforms during the Cenozoic. © 2017 The Author(s).

  7. Assessing the Role of Anhydrite in the KT Mass Extinction: Hints from Shock-loading Experiments

    NASA Technical Reports Server (NTRS)

    Skala, R.; Lnagenhorst, F.; Hoerz, F.

    2004-01-01

    Various killing mechanisms have been suggested to contribute to the mass extinctions at the KT boundary, including severe, global deterioration of the atmosphere and hydrosphere due to SO(x) released from heavily shocked, sulfate-bearing target rocks. The devolatilization of anhydrite is predominantly inferred from thermodynamic considerations and lacks experimental confirmation. To date, the experimentally determined shock behavior of anhydrite is limited to solid-state effects employing X-ray diffraction methods. The present report employs additional methods to characterize experimentally shocked anhydrite.

  8. Inhibition of Rac1 activity in the hippocampus impaired extinction of contextual fear.

    PubMed

    Jiang, Lizhu; Mao, Rongrong; Tong, Jianbin; Li, Jinnan; Chai, Anping; Zhou, Qixin; Yang, Yuexiong; Wang, Liping; Li, Lingjiang; Xu, Lin

    2016-10-01

    Promoting extinction of fear memory is the main treatment of fear disorders, especially post-traumatic stress disorder (PTSD). However, fear extinction is often incomplete in these patients. Our previous study had shown that Rac1 activity in hippocampus plays a crucial role in the learning of contextual fear memory in rats. Here, we further investigated whether Rac1 activity also modulated the extinction of contextual fear memory. We found that massed extinction obviously upregulated hippocampal Rac1 activity and induced long-term extinction of contextual fear in rats. Intrahippocampal injection of the Rac1 inhibitor NSC23766 prevents extinction of contextual fear in massed extinction training rats. In contrast, long-spaced extinction downregulated Rac1 activity and caused less extinction. And Rac1 activator CN04-A promotes extinction of contextual fear in long-spaced extinction rats. Our study demonstrates that inhibition of Rac1 activity in the hippocampus impaired extinction of contextual fear, suggesting that modulating Rac1 activity of the hippocampus may be promising therapy of fear disorders. Copyright © 2016 Elsevier Ltd. All rights reserved.

  9. Meteoritic trace element toxification and the terminal Mesozoic mass extinction

    SciTech Connect

    Dickson, S.M.; Erickson, D.J. III

    1985-01-01

    Calculations of trace element fluxes to the earth associated with 5 and 10 kilometer diameter Cl chondrites and iron meteorites are presented. The data indicate that the masses of certain trace elements contained in the bolide, such as Fe, Co, Ni, Cr, Pb, and Cu, are as large as or larger than the world ocean burden. The authors believe that this pulse of trace elements was of sufficient magnitude to perturb the biogeochemical cycles operative 65 million years ago, a probably time of meteorite impact. Geochemical anomalies in Cretaceous-Tertiary boundary sediments suggest that elevated concentrations of trace elements may havemore » persisted for thousands of years in the ocean. Through direct exposure and bioaccumulation, many trophic levels of the global food chain, including that of the dinosaurs, would have been adversely affected by these meteoritic trace elements. The trace element toxification hypothesis may account for the selective extinction of both marine and terrestrial species in the enigmatic terminal Mesozoic event.« less

  10. Isotopic evidence bearing on Late Triassic extinction events, Queen Charlotte Islands, British Columbia, and implications for the duration and cause of the Triassic/Jurassic mass extinction

    USGS Publications Warehouse

    Ward, P.D.; Garrison, G.H.; Haggart, J.W.; Kring, D.A.; Beattie, M.J.

    2004-01-01

    Stable isotope analyses of Late Triassic to earliest Jurassic strata from Kennecott Point in the Queen Charlotte Islands, British Columbia, Canada shows the presence of two distinct and different organic carbon isotope anomalies at the Norian/Rhaetian and Rhaetian/Hettangian (=Triassic/Jurassic) stage boundaries. At the older of these boundaries, which is marked by the disappearance of the bivalve Monotis, the isotope record shows a series of short-lived positive excursions toward heavier values. Strata approaching this boundary show evidence of increasing anoxia. At the higher boundary, marked by the disappearance of the last remaining Triassic ammonites and over 50 species of radiolarians, the isotopic pattern consists of a series of short duration negative anomalies. The two events, separated by the duration of the Rhaetian age, comprise the end-Triassic mass extinction. While there is no definitive evidence as to cause, the isotopic record does not appear similar to that of the impact-caused Cretaceous/Tertiary boundary extinction. ?? 2004 Published by Elsevier B.V.

  11. Extinction of alcohol seeking is enhanced by compound extinction and the noradrenaline reuptake inhibitor atomoxetine.

    PubMed

    Leung, Hiu T; Corbit, Laura H

    2017-01-01

    Alcohol-related stimuli can trigger relapse of alcohol-seeking behaviors even after extended periods of abstinence. Extinction of such stimuli provides a means for reducing their impact on relapse. However, the expression of extinction can be disrupted by exposure to the previous reinforcer as well as the simple passage of time. We investigated whether augmentation of prediction error or of noradrenaline neurotransmission by the reuptake inhibitor atomoxetine would enhance long-term extinction of alcohol-seeking behavior. Rats received Pavlovian conditioning of multiple stimuli signaling the delivery of an alcohol reward before individual extinction was given to each of these stimuli. Further extinction was then given to a target stimulus presented in compound with another alcohol-predictive stimulus intended to augment prediction error (Experiment 1) or after a systemic injection of atomoxetine (1.0 mg/kg; Experiment 2). Experiment 3 examined whether the compound stimulus effect relied on noradrenergic activity by testing the effects of the β-adrenergic antagonist propranolol, given prior to compound stimulus trials. Long-term retention of extinction learning was assessed a week later. Compound stimulus presentations enhanced long-term extinction as the stimulus extinguished in compound elicited less responding than a stimulus receiving equal extinction alone when tested a week later. This effect was mimicked by atomoxetine and blocked by propranolol given during extinction training. Thus, extinction of alcohol-seeking behavior can be improved by extinguishing multiple alcohol-predictive stimuli or enhancing noradrenaline neurotransmission during extinction training. Both behavioral and neurobiological processes could be exploited to enhance the outcome of extinction-based treatments for alcohol use disorders. © 2015 Society for the Study of Addiction.

  12. Extinctions in ancient and modern seas.

    PubMed

    Harnik, Paul G; Lotze, Heike K; Anderson, Sean C; Finkel, Zoe V; Finnegan, Seth; Lindberg, David R; Liow, Lee Hsiang; Lockwood, Rowan; McClain, Craig R; McGuire, Jenny L; O'Dea, Aaron; Pandolfi, John M; Simpson, Carl; Tittensor, Derek P

    2012-11-01

    In the coming century, life in the ocean will be confronted with a suite of environmental conditions that have no analog in human history. Thus, there is an urgent need to determine which marine species will adapt and which will go extinct. Here, we review the growing literature on marine extinctions and extinction risk in the fossil, historical, and modern records to compare the patterns, drivers, and biological correlates of marine extinctions at different times in the past. Characterized by markedly different environmental states, some past periods share common features with predicted future scenarios. We highlight how the different records can be integrated to better understand and predict the impact of current and projected future environmental changes on extinction risk in the ocean. Copyright © 2012 Elsevier Ltd. All rights reserved.

  13. The Sun-Earth connect 3: lessons from the periodicities of deep time influencing sea-level change and marine extinctions in the geological record.

    PubMed

    Baker, Robert Gv; Flood, Peter G

    2015-01-01

    A number of papers since Rampino and Stothers published in Science 1984 have reported common periodicities in a wide range of climate, geomagnetic, tectonic and biological proxies, including marine extinctions. Single taper and multitaper spectral analysis of marine fluctuations between the Late Cretaceous and the Miocene replicates a number of the published harmonics. Whereas these common periodicities have been argued to have a galactic origin, this paper presents an alternative fractal model based on large scale fluctuations of the magnetic field of the Sun. The fluctuations follow a self-similar matrix of periodicities and the solutions of the differential equation allow for models to be constructed predicting extreme events for solar emissions. A comparison to major Phanerozoic extinction, climate and geomagnetic events, captured in the geological record, show a striking loop symmetry summarised in major 66 Ma irradiance and electromagnetic pulses from the Sun.

  14. Testing Proximate Cause Hypotheses for the End-Ordovician Mass Extinction: Do Patterns of Change in Biomarker Signatures Support a Linkage Between Graptolite and Phytoplankton Community Changes?

    NASA Astrophysics Data System (ADS)

    Marshall, N.; Thomas, E.; Mitchell, C. E.; Aga, D.; Wombacher, R.

    2017-12-01

    The goal of our study is to analyze the biomarkers in the Vinini Creek section based on a set of samples in which graptolite community change has been identified. The study will test several competing hypotheses about the cause of the observed changes in the environmental proxies and the graptolite community structure and composition. The study interval in the Late Ordovician (444.7-443.4 Ma) was a glacial period with varying climate and sea level changes that are marked by geochemical signatures. Climate change drove changes in deep-ocean circulation and upwelling zones during the concomitant mass extinction and it appears that the graptolites inhabiting the mesopelagic zone were the most vulnerable during these events. Due to the high vulnerability of the graptolites in the Vinini Creek section, biomarkers in the section are especially important for interpreting changing ocean conditions. Changing productivity in the upwelling zones of modern oceans is reflected in the microbial community, which forms the base of the food chain and drives biogeochemical cycles. Moreover, microbes can be traced using organism-specific biomarkers. Steranes (C27-C29) are biomarkers for eukaryotic organisms (e.g., green algae) and hopanes (C27-C35) are biomarkers for bacteria. We will determine hopane-sterane ratios, which reflect measurable relative contributions of bacteria and eukaryotes to sedimentary organic matter as a result of fluctuations in the strength of the oxygen minimum zone and associated denitrification processes. Previous work at lower resolution in this section suggests a decrease in denitrification and increase in abundance of eukaryotes (e.g., green algae) relative to bacteria within the Hirnantian glacial lowstand interval, roughly synchronously with the mass extinction. These relationships suggest that climatically driven changes in nutrient cycling and phytoplankton communities drove the mass extinction. If this is so, then changes in graptolite community

  15. Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary

    NASA Astrophysics Data System (ADS)

    Ivany, Linda C.; Patterson, William P.; Lohmann, Kyger C.

    2000-10-01

    The Eocene/Oligocene boundary, at about 33.7Myr ago, marks one of the largest extinctions of marine invertebrates in the Cenozoic period. For example, turnover of mollusc species in the US Gulf coastal plain was over 90% at this time. A temperature change across this boundary-from warm Eocene climates to cooler conditions in the Oligocene-has been suggested as a cause of this extinction event, but climate reconstructions have not provided support for this hypothesis. Here we report stable oxygen isotope measurements of aragonite in fish otoliths-ear stones-collected across the Eocene/Oligocene boundary. Palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval, in agreement with previous studies. From incremental microsampling of otoliths, however, we can resolve the seasonal variation in temperature, recorded as the otoliths continue to accrete new material over the life of the fish. These seasonal data suggest that winters became about 4°C colder across the Eocene/Oligocene boundary. We suggest that temperature variability, rather than change in mean annual temperature, helped to cause faunal turnover during this transition.

  16. Variation in center of mass estimates for extant sauropsids and its importance for reconstructing inertial properties of extinct archosaurs.

    PubMed

    Allen, Vivian; Paxton, Heather; Hutchinson, John R

    2009-09-01

    Inertial properties of animal bodies and segments are critical input parameters for biomechanical analysis of standing and moving, and thus are important for paleobiological inquiries into the broader behaviors, ecology and evolution of extinct taxa such as dinosaurs. But how accurately can these be estimated? Computational modeling was used to estimate the inertial properties including mass, density, and center of mass (COM) for extant crocodiles (adult and juvenile Crocodylus johnstoni) and birds (Gallus gallus; junglefowl and broiler chickens), to identify the chief sources of variation and methodological errors, and their significance. High-resolution computed tomography scans were segmented into 3D objects and imported into inertial property estimation software that allowed for the examination of variable body segment densities (e.g., air spaces such as lungs, and deformable body outlines). Considerable biological variation of inertial properties was found within groups due to ontogenetic changes as well as evolutionary changes between chicken groups. COM positions shift in variable directions during ontogeny in different groups. Our method was repeatable and the resolution was sufficient for accurate estimations of mass and density in particular. However, we also found considerable potential methodological errors for COM related to (1) assumed body segment orientation, (2) what frames of reference are used to normalize COM for size-independent comparisons among animals, and (3) assumptions about tail shape. Methods and assumptions are suggested to minimize these errors in the future and thereby improve estimation of inertial properties for extant and extinct animals. In the best cases, 10%-15% errors in these estimates are unavoidable, but particularly for extinct taxa errors closer to 50% should be expected, and therefore, cautiously investigated. Nonetheless in the best cases these methods allow rigorous estimation of inertial properties. (c) 2009 Wiley

  17. Orbital stability of the unseen solar companion linked to periodic extinction events

    NASA Technical Reports Server (NTRS)

    Torbett, M. V.; Smoluchowski, R.

    1984-01-01

    Evidence from three-dimensional numerical modelling is presented that only cometary orbits with a limited range in inclination with respect to the galactic plane are formally stable for the length of time required to cause periodic extinction events. The calculations were done using Cowell's method employing a fourth-order Runge-Kutta integration scheme in an inertial reference frame in orbit about the Galaxy. Tidal perturbations in the radial direction due to the Galaxy and the Coriolis forces are included. The vertical component of the gravitational field of the galactic disk is superimposed on these forces. The results indicate that orbits for Nemesis that are inclined at more than 30 deg to the galactic plane are not allowed and suggests that the search for Nemesis should be concentrated toward the plane of the Galaxy. Perturbations by passing stars or molecular clouds may make even the low-inclination orbits unstable.

  18. Limitations on K-T mass extinction theories based upon the vertebrate record

    NASA Technical Reports Server (NTRS)

    Archibald, J. David; Bryant, Laurie J.

    1988-01-01

    Theories of extinction are only as good as the patterns of extinction that they purport to explain. Often such patterns are ignored. For the terminal Cretaceous events, different groups of organisms in different environments show different patterns of extinction that to date cannot be explained by a single causal mechanism. Several patterns of extinction (and/or preservational bias) can be observed for the various groups of vertebrates from the uppermost Cretaceous Hell Creek Formation and lower Paleocene Tullock Formation in eastern Montana. The taxonomic level at which the percentage of survivals (or extinctions) is calculated will have an effect upon the perception of faunal turnover. In addition to the better known mammals and better publicized dinosaurs, there are almost 60 additional species of reptiles, birds, amphibians, and fish in the HELL Creek Formation. Simple arithmetic suggests only 33 percent survival of these vertebrates from the Hell Creek Fm. into the Tullock Fm. A more critical examination of the data shows that almost all Hell Creek species not found in the Tullock are represented in one of the following categories; extremely rare forms, elasmobranch fish that underwent rapid speciation taxa that although not known or rare in the Tullock, are found elsewhere. Each of the categories is largely the result of the following biases: taphonomy, ecological differences, taxonomic artifact paleogeography. The two most important factors appear to be the possible taphonomic biases and the taxonomic artifacts. The extinction patterns among the vertebrates do not appear to be attributable to any single cause, catastrophic or otherwise.

  19. Magma-salt interactions and degassing from the Tunguska Basin, Siberia: Towards a new killer model for the P-Tr mass extinction

    NASA Astrophysics Data System (ADS)

    Svensen, H.; Planke, S.; Polozov, A.; Schmidbauer, N.

    2006-12-01

    Life on Earth was severely affected during the Permo-Triasic mass extinction. A 5-10º C global warming and oceanic anoxia accompanied the mass extinction. There is a consensus that massive volcanic eruptions from the Siberian Traps Large igneous province 251 million years ago played a key role in the environmental catastrophe. However, the actual mechanisms are strongly debated. We present new field, geochemical and experimental data that links both the mass extinction and the global warming to processes in the Tunguska Basin in Siberia. The basin is composed of dominantly Cambrian evaporates and Ordovician to Permian marine to terrestrial carbonates, sandstones, shales and coals. During the formation of the Siberian Traps, these sediments were intruded by magmatic sills and dykes. The emplacement resulted in heating of the sedimentary host rocks, gas generation and formation of hundreds of explosion pipes. The pipes are rooted in a 1-2 km thick evaporate sequence (halite, anhydrate, dolostone) and contain brecciated and altered sedimentary and magmatic rocks. Borehole data show intense alteration in the contact aureoles around sill intrusions and around the pipes. Heating experiments of hydrocarbon-bearing evaporates show that gases generated during metamorphism include CO2, SO2 and a range of halocarbons and sulfur-bearing hydrocarbon gases. Furthermore, chloride isotope data from the contact aureoles support a removal of Cl during metamorphism. Our results demonstrate that metamorphism and degassing from the Tunguska Basin provided the necessary components to cause an environmental disaster, including destruction of the Late Permian ozone layer.

  20. Metal-induced malformations in early Palaeozoic plankton are harbingers of mass extinction

    PubMed Central

    Vandenbroucke, Thijs R. A.; Emsbo, Poul; Munnecke, Axel; Nuns, Nicolas; Duponchel, Ludovic; Lepot, Kevin; Quijada, Melesio; Paris, Florentin; Servais, Thomas; Kiessling, Wolfgang

    2015-01-01

    Glacial episodes have been linked to Ordovician–Silurian extinction events, but cooling itself may not be solely responsible for these extinctions. Teratological (malformed) assemblages of fossil plankton that correlate precisely with the extinction events can help identify alternate drivers of extinction. Here we show that metal poisoning may have caused these aberrant morphologies during a late Silurian (Pridoli) event. Malformations coincide with a dramatic increase of metals (Fe, Mo, Pb, Mn and As) in the fossils and their host rocks. Metallic toxins are known to cause a teratological response in modern organisms, which is now routinely used as a proxy to assess oceanic metal contamination. Similarly, our study identifies metal-induced teratology as a deep-time, palaeobiological monitor of palaeo-ocean chemistry. The redox-sensitive character of enriched metals supports emerging ‘oceanic anoxic event' models. Our data suggest that spreading anoxia and redox cycling of harmful metals was a contributing kill mechanism during these devastating Ordovician–Silurian palaeobiological events. PMID:26305681

  1. Metal-induced malformations in early Palaeozoic plankton are harbingers of mass extinction

    NASA Astrophysics Data System (ADS)

    Vandenbroucke, Thijs R. A.; Emsbo, Poul; Munnecke, Axel; Nuns, Nicolas; Duponchel, Ludovic; Lepot, Kevin; Quijada, Melesio; Paris, Florentin; Servais, Thomas; Kiessling, Wolfgang

    2015-08-01

    Glacial episodes have been linked to Ordovician-Silurian extinction events, but cooling itself may not be solely responsible for these extinctions. Teratological (malformed) assemblages of fossil plankton that correlate precisely with the extinction events can help identify alternate drivers of extinction. Here we show that metal poisoning may have caused these aberrant morphologies during a late Silurian (Pridoli) event. Malformations coincide with a dramatic increase of metals (Fe, Mo, Pb, Mn and As) in the fossils and their host rocks. Metallic toxins are known to cause a teratological response in modern organisms, which is now routinely used as a proxy to assess oceanic metal contamination. Similarly, our study identifies metal-induced teratology as a deep-time, palaeobiological monitor of palaeo-ocean chemistry. The redox-sensitive character of enriched metals supports emerging `oceanic anoxic event' models. Our data suggest that spreading anoxia and redox cycling of harmful metals was a contributing kill mechanism during these devastating Ordovician-Silurian palaeobiological events.

  2. Adrenergic Transmission Facilitates Extinction of Conditional Fear in Mice

    ERIC Educational Resources Information Center

    Barad, Mark; Cain, Christopher K.; Blouin, Ashley M.

    2004-01-01

    Extinction of classically conditioned fear, like its acquisition, is active learning, but little is known about its molecular mechanisms. We recently reported that temporal massing of conditional stimulus (CS) presentations improves extinction memory acquisition, and suggested that temporal spacing was less effective because individual CS…

  3. Adaptive radiation of multituberculate mammals before the extinction of dinosaurs.

    PubMed

    Wilson, Gregory P; Evans, Alistair R; Corfe, Ian J; Smits, Peter D; Fortelius, Mikael; Jernvall, Jukka

    2012-03-14

    The Cretaceous-Paleogene mass extinction approximately 66 million years ago is conventionally thought to have been a turning point in mammalian evolution. Prior to that event and for the first two-thirds of their evolutionary history, mammals were mostly confined to roles as generalized, small-bodied, nocturnal insectivores, presumably under selection pressures from dinosaurs. Release from these pressures, by extinction of non-avian dinosaurs at the Cretaceous-Paleogene boundary, triggered ecological diversification of mammals. Although recent individual fossil discoveries have shown that some mammalian lineages diversified ecologically during the Mesozoic era, comprehensive ecological analyses of mammalian groups crossing the Cretaceous-Paleogene boundary are lacking. Such analyses are needed because diversification analyses of living taxa allow only indirect inferences of past ecosystems. Here we show that in arguably the most evolutionarily successful clade of Mesozoic mammals, the Multituberculata, an adaptive radiation began at least 20 million years before the extinction of non-avian dinosaurs and continued across the Cretaceous-Paleogene boundary. Disparity in dental complexity, which relates to the range of diets, rose sharply in step with generic richness and disparity in body size. Moreover, maximum dental complexity and body size demonstrate an adaptive shift towards increased herbivory. This dietary expansion tracked the ecological rise of angiosperms and suggests that the resources that were available to multituberculates were relatively unaffected by the Cretaceous-Paleogene mass extinction. Taken together, our results indicate that mammals were able to take advantage of new ecological opportunities in the Mesozoic and that at least some of these opportunities persisted through the Cretaceous-Paleogene mass extinction. Similar broad-scale ecomorphological inventories of other radiations may help to constrain the possible causes of mass extinctions.

  4. StarHorse: a Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars

    NASA Astrophysics Data System (ADS)

    Queiroz, A. B. A.; Anders, F.; Santiago, B. X.; Chiappini, C.; Steinmetz, M.; Dal Ponte, M.; Stassun, K. G.; da Costa, L. N.; Maia, M. A. G.; Crestani, J.; Beers, T. C.; Fernández-Trincado, J. G.; García-Hernández, D. A.; Roman-Lopes, A.; Zamora, O.

    2018-05-01

    Understanding the formation and evolution of our Galaxy requires accurate distances, ages, and chemistry for large populations of field stars. Here, we present several updates to our spectrophotometric distance code, which can now also be used to estimate ages, masses, and extinctions for individual stars. Given a set of measured spectrophotometric parameters, we calculate the posterior probability distribution over a given grid of stellar evolutionary models, using flexible Galactic stellar-population priors. The code (called StarHorse) can accommodate different observational data sets, prior options, partially missing data, and the inclusion of parallax information into the estimated probabilities. We validate the code using a variety of simulated stars as well as real stars with parameters determined from asteroseismology, eclipsing binaries, and isochrone fits to star clusters. Our main goal in this validation process is to test the applicability of the code to field stars with known Gaia-like parallaxes. The typical internal precisions (obtained from realistic simulations of an APOGEE+Gaia-like sample) are {˜eq } 8 {per cent} in distance, {˜eq } 20 {per cent} in age, {˜eq } 6 {per cent} in mass, and ≃ 0.04 mag in AV. The median external precision (derived from comparisons with earlier work for real stars) varies with the sample used, but lies in the range of {˜eq } [0,2] {per cent} for distances, {˜eq } [12,31] {per cent} for ages, {˜eq } [4,12] {per cent} for masses, and ≃ 0.07 mag for AV. We provide StarHorse distances and extinctions for the APOGEE DR14, RAVE DR5, GES DR3, and GALAH DR1 catalogues.

  5. Star formation and extinct radioactivities

    NASA Technical Reports Server (NTRS)

    Cameron, A. G. W.

    1984-01-01

    An assessment is made of the evidence for the existence of now-extinct radioactivities in primitive solar system material, giving attention to implications for the early stages of sun and solar system formation. The characteristics of possible disturbances in dense molecular clouds which can initiate the formation of cloud cores is discussed, with emphasis on these disturbances able to generate fresh radioactivities. A one-solar mass red giant star on the asymptotic giant branch appears to have been the best candidate to account for the short-lived extinct radioactivities in the early solar system.

  6. Early Triassic alternative ecological states driven by anoxia, hyperthermals, and erosional pulses following the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Pietsch, C.; Petsios, E.; Bottjer, D. J.

    2015-12-01

    The end-Permian mass extinction, 252 million years ago, was the most devastating loss of biodiversity in Earth's history. Massive volcanic eruptions of the Siberian Traps and the concurrent burning of coal, carbonate, and evaporite deposits emplaced greenhouse and toxic gasses. Hyperthermal events of the surface ocean, up to 40°C, led to reduced gradient-driven ocean circulation which yielded extensive equatorial oxygen minimum zones. Today, anthropogenic greenhouse gas production is outpacing carbon input modeled for the end-Permian mass extinction, which suggests that modern ecosystems may yet experience a severe biotic crisis. The Early Triassic records the 5 million year aftermath of the end-Permian mass extinction and is often perceived as an interval of delayed recovery. We combined a new, high resolution carbon isotope record, sedimentological analysis, and paleoecological collections from the Italian Werfen Formation to fully integrate paleoenvironmental change with the benthic ecological response. We find that the marine ecosystem experienced additional community restructuring events due to subsequent hyperthermal events and pulses of erosion. The benthic microfauna and macrofauna both contributed to disaster communities that initially rebounded in the earliest Triassic. 'Disaster fauna' including microbialites, microconchids, foraminifera, and "flat clams" took advantage of anoxic conditions in the first ~500,000 years, dominating the benthic fauna. Later, in the re-oxygenated water column, opportunistic disaster groups were supplanted by a more diverse, mollusc-dominated benthic fauna and a complex ichnofauna. An extreme temperature run-up beginning in the Late Dienerian led to an additional hyperthermal event in the Late-Smithian which co-occurred with increased humidity and terrestrial run-off. Massive siliciclastic deposits replaced carbonate deposition which corresponds to the infaunalization of the benthic fauna. The disaster taxa dominated

  7. Getting the measure of extinction.

    PubMed

    Mace, G

    1998-01-01

    Like all species, plants, mammals, and birds have been subject to extinction as a fundamental part of evolution. Indeed, only about 2-4% of all the species that have ever lived during the 600 million years of the fossil record still survive today. Looking at the fossil record, it can be said that invertebrate species and mammals have had an average life span of 5-10 and 1-2 million years, respectively. More recent extinction records for birds and mammals lost over the last half of the century indicate that 1 out of 14,000 species becomes extinct each year, giving each species an average life span of 10,000 years--100 to 1000 times shorter than the lifetime of species in the fossil record. Drawing on the World's Conservation Union Red List of threatened animals (1996), species lifetimes of birds, mammals and reptiles are estimated at 300-500 years and 100-1000 years across broader groups. In general, these estimates show that extinction rates today are 1000 to 10,000 times higher than in the past, making current rates of species loss at least equivalent to the mass extinctions in the past. A major difference, however, is the fact that almost all extinctions that have transpired today are due to the impact of human activities.

  8. Investigating A Unique Open Ocean Geochemical Record Of the End Triassic Mass Extinction from Panthalassa

    NASA Astrophysics Data System (ADS)

    Marroquín, S. M.; Gill, B. C.; Them, T. R., II; Trabucho-Alexandre, J. P.; Aberhan, M.; Owens, J. D.; Gröcke, D. R.; Caruthers, A. H.

    2017-12-01

    The end-Triassic mass extinction ( 201 Ma) was a time of intense disturbance for marine communities. This event is estimated to have produced as much as a loss of 80% of known marine species. The protracted interval of elevated extinction rates is also characterized by a major carbon cycle perturbation and potentially widespread oxygen deficiency within the oceans. While the causes of extinction and environmental feedbacks are still debated it is hypothesized to have been triggered by massive volcanism associated with the Central Atlantic Magmatic Province flood basalts. However, our understanding of the Latest Triassic-Earliest Jurassic interval is limited due to the lack of well-preserved stratigraphic successions outside of the Tethys Ocean (present day Europe), with most of the records from epicontinental and marginal marine settings. To expand our understanding of this critical interval, our study seeks to document biological and environmental changes elsewhere. Specifically, we document and reconstruct these changes in the equatorial Panthalassan Ocean. We will present new data from a sedimentary succession preserved in the Wrangell Mountains of Alaska that spans the Late Triassic through Early Jurassic. The sedimentary succession represents a mixed carbonate-siliciclastic ramp that was deposited at tropical latitudes, adjacent to an island arc in the open Panthalassan Ocean. This succession affords a unique view of open marine conditions, and also holds the potential for excellent temporal control as it contains abundant ash layers throughout, as well as, key ammonite and bivalve fossil occurrences that provide biostratigraphic control. We will present an integrated geochemical and paleontological record from this site using several geochemical proxies (carbon, δ13Ccarb and % total organic carbon, sulfur, δ34S, as well as pyrite contents and iron speciation) along with ammonite and bivalve occurrence data to reconstruct the record of environmental and

  9. Global bioevents and the question of periodicity

    NASA Astrophysics Data System (ADS)

    Sepkoski, J. John

    The hypothesis of periodicity in extinction is an empirical claim that extinction events, while variable in magnitude, are regular in timing and therefore are serially dependent upon some single, ultimate cause with clocklike behavior. This hypothesis is controversal, in part because of questions regarding the identity and timing of certain extinction events and because of speculations concerning possible catastrophic extraterrestrial forcing mechanisms. New data on extinctions of marine animal genera are presented that display a high degree of periodicity in the Mesozoic and Cenozoic as well as a suggestion of nonstationary periodicity in the late Paleozoic. However, no periodicity is evident among the as yet poorly documented extinction events of the early and middle Paleozoic.

  10. Extinction and the spatial dynamics of biodiversity

    PubMed Central

    Jablonski, David

    2008-01-01

    The fossil record amply shows that the spatial fabric of extinction has profoundly shaped the biosphere; this spatial dimension provides a powerful context for integration of paleontological and neontological approaches. Mass extinctions evidently alter extinction selectivity, with many factors losing effectiveness except for a positive relation between survivorship and geographic range at the clade level (confirmed in reanalyses of end-Cretaceous extinction data). This relation probably also holds during “normal” times, but changes both slope and intercept with increasing extinction. The strong geographical component to clade dynamics can obscure causation in the extinction of a feature or a clade, owing to hitchhiking effects on geographic range, so that multifactorial analyses are needed. Some extinctions are spatially complex, and regional extinctions might either reset a diversity ceiling or create a diversification debt open to further diversification or invasion. Evolutionary recoveries also exhibit spatial dynamics, including regional differences in invasibilty, and expansion of clades from the tropics fuels at least some recoveries, as well as biodiversity dynamics during normal times. Incumbency effects apparently correlate more closely with extinction intensities than with standing diversities, so that regions with higher local and global extinctions are more subject to invasion; the latest Cenozoic temperate zones evidently received more invaders than the tropics or poles, but this dynamic could shift dramatically if tropical diversity is strongly depleted. The fossil record can provide valuable insights, and their application to present-day issues will be enhanced by partitioning past and present-day extinctions by driving mechanism rather than emphasizing intensity. PMID:18695229

  11. When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa

    PubMed Central

    Day, Michael O.; Ramezani, Jahandar; Bowring, Samuel A.; Sadler, Peter M.; Erwin, Douglas H.; Abdala, Fernando; Rubidge, Bruce S.

    2015-01-01

    A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian–Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite attempts to identify a similar biodiversity crisis in the terrestrial realm, the low resolution of mid-Permian tetrapod biostratigraphy and a lack of robust geochronological constraints have until now hampered both the correlation and quantification of terrestrial extinctions. Here we present an extensive compilation of tetrapod-stratigraphic data analysed by the constrained optimization (CONOP) algorithm that reveals a significant extinction event among tetrapods within the lower Beaufort Group of the Karoo Basin, South Africa, in the latest Capitanian. Our fossil dataset reveals a 74–80% loss of generic richness between the upper Tapinocephalus Assemblage Zone (AZ) and the mid-Pristerognathus AZ that is temporally constrained by a U–Pb zircon date (CA-TIMS method) of 260.259 ± 0.081 Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens the biochronology of the Permian Beaufort Group and supports the existence of a mid-Permian mass extinction event on land near the end of the Guadalupian. Our results permit a temporal association between the extinction of dinocephalian therapsids and the LIP volcanism at Emeishan, as well as the marine end-Guadalupian extinctions. PMID:26156768

  12. Mass extinctions, atmospheric sulphur and climatic warming at the K/T boundary

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Volk, Tyler

    1988-01-01

    The possible climatic effects of a drastic decrease in cloud condensation nuclei (CCN) associated with a severe reduction in the global marine phytoplankton abundance are investigated. Calculations suggest that a reduction in CCN of more than 80 percent and the resulting decrease in marine cloud albedo could have produced a rapid global warming of 6 C or more. Oxygen isotope analyses of marine sediments from many parts of the world have been interpreted as indicating a marked warming coincident with the demise of calcareous nannoplankton at the K/T boundary. Decreased marine cloud albedo and resulting high sea surface temperatures could have been a factor in the maintenance of low productivity in the 'Strangelove Ocean' period following the K/T extinctions.

  13. Long-term oceanic changes prior the end-Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Clémence, Marie-Emilie; Mette, Wolfgang; Thibault, Nicolas; Korte, Christoph

    2014-05-01

    A number of potential causes and kill mechanisms have been proposed for the end-Triassic mass extinction such as palaeoclimatic and sea-level variations, massive volcanism and ocean acidification. Recent analysis of the stomatal index and density of fossil leaves and geochemical research on pedogenic carbonate nodules are suggestive of rising atmospheric CO2 concentration and fluctuating climate in the Rhaetian. It seems therefore probable that the end-Triassic event was preceded by large climatic fluctuations and environmental perturbations in the Rhaetian which might have partly affected the composition and diversity of the terrestrial and marine biota prior to the end-Triassic interval. The Northern Calcareous Alps (NCA) has long been favored for the study of the Rhaetian, since the GSSP of the Triassic/Jurassic (T/J) boundary and other important T/J sections are situated in this region. However, the most famous Rhaetian sections in the NCA are composed of carbonates from the Koessen Formation and were situated in a large isolated intraplatform Basin (the Eiberg Basin), bordered to the south-east by a well-developed coral reef in the NW of the Tethys border. Several Rhaetian sections composed of marls and shales of the Zlambach Formation were deposited at the same time on the other side of this reef, in the oceanic Halstatt Basin, which was in direct connection to the Tethys. Here, we present new results on sedimentology, stable isotope and trace element analysis of both intraplatform and oceanic basin deposits in the NCA. Intraplatform Rhaetian sections from the Koessen Formation bear a few minor intervals of shales with enrichments in organic matter, some of which are associated to carbon isotopic excursions. Oceanic sections from the Hallstatt Basin are characterized at the base by very cyclic marl-limestone alternations. Higher up in the section, sediments progressively turn into pure shale deposits and the top of the Formation is characterized by organic

  14. Extinction and anti-extinction: the "attentional waiting" hypothesis.

    PubMed

    Watling, Rosamond; Danckert, James; Linnell, Karina J; Cocchini, Gianna

    2013-03-01

    Patients with visual extinction have difficulty detecting a single contralesional stimulus when a second stimulus is simultaneously presented on the ipsilesional side. The rarely reported phenomenon of visual anti-extinction describes the opposite behavior, in which patients show greater difficulty in reporting a stimulus presented in isolation than they do in reporting 2 simultaneously presented stimuli. S. J. Goodrich and R. Ward (1997, Anti-extinction following unilateral parietal damage, Cognitive Neuropsychology, Vol. 14, pp. 595-612) suggested that visual anti-extinction is the result of a task-specific mechanism in which processing of the ipsilesional stimulus facilitates responses to the contralesional stimulus; in contrast, G. W. Humphreys, M. J. Riddoch, G. Nys, and D. Heinke (2002, Transient binding by time: Neuropsychological evidence from anti-extinction, Cognitive Neuropsychology, Vol. 19, pp. 361-380) suggested that temporal binding groups contralesional and ipsilesional stimuli together at brief exposure durations. We investigated extinction and anti-extinction phenomena in 3 brain-damaged patients using an extinction paradigm in which the stimulus exposure duration was systematically manipulated. Two patients showed both extinction and anti-extinction depending on the exposure duration of stimuli. Data confirmed the crucial role of duration in modulating the effect of extinction and anti-extinction. However, contrary to Humphreys and colleagues' (2002) single case, our patients showed extinction for short and anti-extinction for long exposure durations, suggesting that different mechanisms might underlie our patients' pattern of data. We discuss a novel "attentional waiting" hypothesis, which proposes that anti-extinction may be observed in patients showing extinction if the exposure duration of stimuli is increased. PsycINFO Database Record (c) 2013 APA, all rights reserved.

  15. An evaluation of criteria that may be used to identify species surviving a mass extinction

    NASA Technical Reports Server (NTRS)

    Macleod, N.

    1994-01-01

    One of the most difficult obstacles to establishing a causal connection between mass extinctions and large body impacts is the existence of what appear to be many more KT survivor species than previously suspected. Though interpretations of 'Cretaceous' faunal elements in lowermost Danian sediments differ, this enigmatic fauna has not been recovered from every biozone-complete boundary section, including the El Kef stratotype. In terms of their potential for providing constraints on scenarios seeking to account for the KT extinction event, the significance of such observations cannot be overstated. Owing to the consistency with which these observations have been made over the last several years, the possibility of widespread trans-KT biotic survivorship can no longer be dismissed. Rather, the survivorship hypothesis must be tested alongside its alternative (the reworking hypothesis) to determine which explains the available data in the most complete yet parsimonious manner. Moreover, valid tests for survivorship cannot be based on negative evidence or on the assumption that only a small cohort of species could have survived the KT boundary event. Several authors have recently proposed various criteria that might be used to test alternative interpretations for this aspect lowermost Danian biotic record.

  16. Boreal earliest Triassic biotas elucidate globally depauperate hard substrate communities after the end-Permian mass extinction.

    PubMed

    Zatoń, Michał; Niedźwiedzki, Grzegorz; Blom, Henning; Kear, Benjamin P

    2016-11-08

    The end-Permian mass extinction constituted the most devastating biotic crisis of the Phanerozoic. Its aftermath was characterized by harsh marine conditions incorporating volcanically induced oceanic warming, widespread anoxia and acidification. Bio-productivity accordingly experienced marked fluctuations. In particular, low palaeolatitude hard substrate communities from shallow seas fringing Western Pangaea and the Tethyan Realm were extremely impoverished, being dominated by monogeneric colonies of filter-feeding microconchid tubeworms. Here we present the first equivalent field data for Boreal hard substrate assemblages from the earliest Triassic (Induan) of East Greenland. This region bordered a discrete bio-realm situated at mid-high palaeolatitude (>30°N). Nevertheless, hard substrate biotas were compositionally identical to those from elsewhere, with microconchids encrusting Claraia bivalves and algal buildups on the sea floor. Biostratigraphical correlation further shows that Boreal microconchids underwent progressive tube modification and unique taxic diversification concordant with changing habitats over time. We interpret this as a post-extinction recovery and adaptive radiation sequence that mirrored coeval subequatorial faunas, and thus confirms hard substrate ecosystem depletion as a hallmark of the earliest Triassic interval globally.

  17. Boreal earliest Triassic biotas elucidate globally depauperate hard substrate communities after the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Zatoń, Michał; Niedźwiedzki, Grzegorz; Blom, Henning; Kear, Benjamin P.

    2016-11-01

    The end-Permian mass extinction constituted the most devastating biotic crisis of the Phanerozoic. Its aftermath was characterized by harsh marine conditions incorporating volcanically induced oceanic warming, widespread anoxia and acidification. Bio-productivity accordingly experienced marked fluctuations. In particular, low palaeolatitude hard substrate communities from shallow seas fringing Western Pangaea and the Tethyan Realm were extremely impoverished, being dominated by monogeneric colonies of filter-feeding microconchid tubeworms. Here we present the first equivalent field data for Boreal hard substrate assemblages from the earliest Triassic (Induan) of East Greenland. This region bordered a discrete bio-realm situated at mid-high palaeolatitude (>30°N). Nevertheless, hard substrate biotas were compositionally identical to those from elsewhere, with microconchids encrusting Claraia bivalves and algal buildups on the sea floor. Biostratigraphical correlation further shows that Boreal microconchids underwent progressive tube modification and unique taxic diversification concordant with changing habitats over time. We interpret this as a post-extinction recovery and adaptive radiation sequence that mirrored coeval subequatorial faunas, and thus confirms hard substrate ecosystem depletion as a hallmark of the earliest Triassic interval globally.

  18. Big cat, small cat: reconstructing body size evolution in living and extinct Felidae.

    PubMed

    Cuff, A R; Randau, M; Head, J; Hutchinson, J R; Pierce, S E; Goswami, A

    2015-08-01

    The evolution of body mass is a fundamental topic in evolutionary biology, because it is closely linked to manifold life history and ecological traits and is readily estimable for many extinct taxa. In this study, we examine patterns of body mass evolution in Felidae (Placentalia, Carnivora) to assess the effects of phylogeny, mode of evolution, and the relationship between body mass and prey choice in this charismatic mammalian clade. Our data set includes 39 extant and 26 extinct taxa, with published body mass data supplemented by estimates based on condylobasal length. These data were run through 'SURFACE' and 'bayou' to test for patterns of body mass evolution and convergence between taxa. Body masses of felids are significantly different among prey choice groupings (small, mixed and large). We find that body mass evolution in cats is strongly influenced by phylogeny, but different patterns emerged depending on inclusion of extinct taxa and assumptions about branch lengths. A single Ornstein-Uhlenbeck optimum best explains the distribution of body masses when first-occurrence data were used for the fossil taxa. However, when mean occurrence dates or last known occurrence dates were used, two selective optima for felid body mass were recovered in most analyses: a small optimum around 5 kg and a large one around 100 kg. Across living and extinct cats, we infer repeated evolutionary convergences towards both of these optima, but, likely due to biased extinction of large taxa, our results shift to supporting a Brownian motion model when only extant taxa are included in analyses. © 2015 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2015 European Society For Evolutionary Biology.

  19. Cholinergic regulation of fear learning and extinction.

    PubMed

    Wilson, Marlene A; Fadel, Jim R

    2017-03-01

    Cholinergic activation regulates cognitive function, particularly long-term memory consolidation. This Review presents an overview of the anatomical, neurochemical, and pharmacological evidence supporting the cholinergic regulation of Pavlovian contextual and cue-conditioned fear learning and extinction. Basal forebrain cholinergic neurons provide inputs to neocortical regions and subcortical limbic structures such as the hippocampus and amygdala. Pharmacological manipulations of muscarinic and nicotinic receptors support the role of cholinergic processes in the amygdala, hippocampus, and prefrontal cortex in modulating the learning and extinction of contexts or cues associated with threat. Additional evidence from lesion studies and analysis of in vivo acetylcholine release with microdialysis similarly support a critical role of cholinergic neurotransmission in corticoamygdalar or corticohippocampal circuits during acquisition of fear extinction. Although a few studies have suggested a complex role of cholinergic neurotransmission in the cellular plasticity essential for extinction learning, more work is required to elucidate the exact cholinergic mechanisms and physiological role of muscarinic and nicotinic receptors in these fear circuits. Such studies are important for elucidating the role of cholinergic neurotransmission in disorders such as posttraumatic stress disorder that involve deficits in extinction learning as well as for developing novel therapeutic approaches for such disorders. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  20. The Triassic dicynodont Kombuisia (Synapsida, Anomodontia) from Antarctica, a refuge from the terrestrial Permian-Triassic mass extinction.

    PubMed

    Fröbisch, Jörg; Angielczyk, Kenneth D; Sidor, Christian A

    2010-02-01

    Fossils from the central Transantarctic Mountains in Antarctica are referred to a new species of the Triassic genus Kombuisia, one of four dicynodont lineages known to survive the end-Permian mass extinction. The specimens show a unique combination of characters only present in this genus, but the new species can be distinguished from the type species of the genus, Kombuisia frerensis, by the presence of a reduced but slit-like pineal foramen and the lack of contact between the postorbitals. Although incomplete, the Antarctic specimens are significant because Kombuisia was previously known only from the South African Karoo Basin and the new specimens extend the taxon's biogeographic range to a wider portion of southern Pangaea. In addition, the new finds extend the known stratigraphic range of Kombuisia from the Middle Triassic subzone B of the Cynognathus Assemblage Zone into rocks that are equivalent in age to the Lower Triassic Lystrosaurus Assemblage Zone, shortening the proposed ghost lineage of this taxon. Most importantly, the occurrence of Kombuisia and Lystrosaurus mccaigi in the Lower Triassic of Antarctica suggests that this area served as a refuge from some of the effects of the end-Permian extinction. The composition of the lower Fremouw Formation fauna implies a community structure similar to that of the ecologically anomalous Lystrosaurus Assemblage Zone of South Africa, providing additional evidence for widespread ecological disturbance in the extinction's aftermath.

  1. Ecological response to collapse of the biological pump following the mass extinction at the Cretaceous-Paleogene boundary

    NASA Astrophysics Data System (ADS)

    Vellekoop, Johan; Woelders, Lineke; Açikalin, Sanem; Smit, Jan; van de Schootbrugge, Bas; Yilmaz, Ismail Ö.; Brinkhuis, Henk; Speijer, Robert P.

    2017-02-01

    It is commonly accepted that the mass extinction associated with the Cretaceous-Paleogene (K-Pg) boundary (˜ 66 Ma) is related to the environmental effects of a large extraterrestrial impact. The biological and oceanographic consequences of the mass extinction are, however, still poorly understood. According to the Living Ocean model, the biological crisis at the K-Pg boundary resulted in a long-term reduction of export productivity in the early Paleocene. Here, we combine organic-walled dinoflagellate cyst (dinocyst) and benthic foraminiferal analyses to provide new insights into changes in the coupling of pelagic and benthic ecosystems. To this end, we perform dinocyst and benthic foraminiferal analyses on the recently discovered Tethyan K-Pg boundary section at Okçular, Turkey, and compare the results with other K-Pg boundary sites in the Tethys. The post-impact dominance of epibenthic morphotypes and an increase of inferred heterotrophic dinocysts in the early Paleocene at Okçular are consistent with published records from other western Tethyan sites. Together, these records indicate that during the early Paleocene more nutrients remained available for the Tethyan planktonic community, whereas benthic communities were deprived of food. Hence, in the post-impact phase the reduction of export productivity likely resulted in enhanced recycling of nutrients in the upper part of the water column, all along the western Tethyan margins.

  2. The Lilliput Effect in Colonial Organisms: Cheilostome Bryozoans at the Cretaceous–Paleogene Mass Extinction

    PubMed Central

    Sogot, Caroline E.; Harper, Elizabeth M.; Taylor, Paul D.

    2014-01-01

    Consistent trends towards decreasing body size in the aftermath of mass extinctions – Lilliput effects – imply a predictable response among unitary animals to these events. The occurrence of Lilliput effects has yet to be widely tested in colonial organisms, which are of particular interest as size change may potentially occur at the two hierarchical levels of the colony and the individual zooids. Bryozoans are particularly useful organisms in which to study colonial size response as they have well-defined zooids. Additionally, a number of analyses of present-day bryozoans have shown that zooid size reflects local environmental conditions, most notably seawater temperature and possibly also food supply. Following the hypothesised decline in primary productivity at the Cretaceous–Paleogene (K–Pg) mass extinction, it is predicted that bryozoan zooid size should decline in the early Paleogene, resulting in a Lilliput effect. To test this prediction, zooid size was compared across the K–Pg boundary at the assemblage level and also within 4 surviving genera. Analysis of 59 bryozoan species from assemblages on either side of the K–Pg boundary showed no significant change in zooid length. Zooid size was also measured in 98 Maastrichtian colonies and 162 Danian colonies belonging to four congeneric species. Only one of these genera showed a significant size decrease across the K–Pg boundary, the other three maintaining constant zooidal lengths, widths and areas. Additionally, the sizes of 210 Maastrichtian colonies and 163 Danian colonies did not show consistent size decrease across the K–Pg boundary in these same species, although maximum colony size did decline in three out of four genera. Furthermore, this lack of consistent size change is uniform between two distinct biogeographical regions, Denmark and the southeastern USA. PMID:24505275

  3. High-precision geochronology confirms voluminous magmatism before, during, and after Earth’s most severe extinction

    PubMed Central

    Burgess, Seth D.; Bowring, Samuel A.

    2015-01-01

    The end-Permian mass extinction was the most severe in the Phanerozoic, extinguishing more than 90% of marine and 75% of terrestrial species in a maximum of 61 ± 48 ky. Because of broad temporal coincidence between the biotic crisis and one of the most voluminous continental volcanic eruptions since the origin of animals, the Siberian Traps large igneous province (LIP), a causal connection has long been suggested. Magmatism is hypothesized to have caused rapid injection of massive amounts of greenhouse gases into the atmosphere, driving climate change and subsequent destabilization of the biosphere. Establishing a causal connection between magmatism and mass extinction is critically dependent on accurately and precisely knowing the relative timing of the two events and the flux of magma. New U/Pb dates on Siberian Traps LIP lava flows, sills, and explosively erupted rocks indicate that (i) about two-thirds of the total lava/pyroclastic volume was erupted over ~300 ky, before and concurrent with the end-Permian mass extinction; (ii) eruption of the balance of lavas continued for at least 500 ky after extinction cessation; and (iii) massive emplacement of sills into the shallow crust began concomitant with the mass extinction and continued for at least 500 ky into the early Triassic. This age model is consistent with Siberian Traps LIP magmatism as a trigger for the end-Permian mass extinction and suggests a role for magmatism in suppression of post-extinction biotic recovery. PMID:26601239

  4. The FMOS-COSMOS survey of star-forming galaxies at z ∼ 1.6. II. The mass-metallicity relation and the dependence on star formation rate and dust extinction

    SciTech Connect

    Zahid, H. J.; Sanders, D. B.; Chu, J.

    We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate (SFR), and dust content of star-forming galaxies at z ∼ 1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity (MZ) relation at z ∼ 1.6 is steeper than the relation observed in the local universe. The steeper MZ relation at z ∼ 1.6 is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at z ∼ 1.6. The most massive galaxies at z ∼ 1.6 (∼10{sup 11} M {sub ☉})more » are enriched to the level observed in massive galaxies in the local universe. The MZ relation we measure at z ∼ 1.6 supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and SFR for galaxies at a fixed stellar mass at z ∼ 1.6, which is similar to trends observed in the local universe. We do not find a relation between stellar mass, metallicity, and SFR that is independent of redshift; rather, our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity, and dust extinction, and find that at a fixed stellar mass, dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs, and dust extinctions, we conclude that stellar mass is most closely related to dust extinction.« less

  5. Multiple sulfur-isotopic evidence for a shallowly stratified ocean following the Triassic-Jurassic boundary mass extinction

    NASA Astrophysics Data System (ADS)

    Luo, Genming; Richoz, Sylvain; van de Schootbrugge, Bas; Algeo, Thomas J.; Xie, Shucheng; Ono, Shuhei; Summons, Roger E.

    2018-06-01

    The cause of the Triassic-Jurassic (Tr-J) boundary biotic crisis, one of the 'Big Five' mass extinctions of the Phanerozoic, remains controversial. In this study, we analyzed multiple sulfur-isotope compositions (δ33S, δ34S and δ36S) of pyrite and Spy/TOC ratios in two Tr-J successions (Mariental, Mingolsheim) from the European Epicontinental Seaway (EES) in order to better document ocean-redox variations during the Tr-J transition. Our results show that upper Rhaetian strata are characterized by 34S-enriched pyrite, low Spy/TOC ratios, and values of Δ33Spy (i.e., the deviation from the mass-dependent array) lower than that estimated for contemporaneous seawater sulfate, suggesting an oxic-suboxic depositional environment punctuated by brief anoxic events. The overlying Hettangian strata exhibit relatively 34S-depleted pyrite, high Δ33Spy, and Spy/TOC values, and the presence of green sulfur bacterial biomarkers indicate a shift toward to euxinic conditions. The local development of intense marine anoxia thus postdated the Tr-J mass extinction, which does not provide support for the hypothesis that euxinia was the main killing agent at the Tr-J transition. Sulfur and organic carbon isotopic records that reveal a water-depth gradient (i.e., more 34S-, 13C-depleted with depth) in combination with Spy/TOC data suggest that the earliest Jurassic EES was strongly stratified, with a chemocline located at shallow depths just below storm wave base. Shallow oceanic stratification may have been a factor for widespread deposition of black shales, a large positive shift in carbonate δ13C values, and a delay in the recovery of marine ecosystems following the Tr-J boundary crisis.

  6. Heavy metal toxicity as a kill mechanism in impact caused mass extinctions

    NASA Technical Reports Server (NTRS)

    Wdowiak, T. J.; Davenport, S. A.; Jones, D. D.; Wdowiak, P.

    1988-01-01

    Heavy metals that are known to be toxic exist in carbonaceous chrondrites at abundances considerably in excess to that of the terrestrial crust. An impactor of relatively undifferentiated cosmic matter would inject into the terrestrial environment large quantities of toxic elements. The abundances of toxic metals found in the Allende CV carbonaceous chondrite and the ratio of meteoritic abundance to crustal abundance are: Cr, 3630 PPM, 30X; Co, 662 PPM, 23X; ni, 13300 PPm, 134X; se, 8.2 PPM, 164X; Os, 0.828 PPM, 166X. The resulting areal density for global dispersal of impactor derived heavy metals and their dilution with terrestrial ejecta are important factors in the determination of the significance of impactor heavy metal toxicity as a kill mechanism in impact caused mass extinctions. A 10 km-diameter asteroid having a density of 3 gram per cu cm would yield a global areal density of impact dispersed chondritic material of 3 kg per square meter. The present areal density of living matter on the terrestrial land surface is 1 kg per square meter. Dilution of impactor material with terrestrial ejecta is determined by energetics, with the mass of ejecta estimated to be in the range of 10 to 100 times that of the mass of the impactor. Because a pelagic impact would be the most likely case, the result would be a heavy metal rainout.

  7. Current extinction rates of reptiles and amphibians.

    PubMed

    Alroy, John

    2015-10-20

    There is broad concern that a mass extinction of amphibians and reptiles is now underway. Here I apply an extremely conservative Bayesian method to estimate the number of recent amphibian and squamate extinctions in nine important tropical and subtropical regions. The data stem from a combination of museum collection databases and published site surveys. The method computes an extinction probability for each species by considering its sighting frequency and last sighting date. It infers hardly any extinction when collection dates are randomized and it provides underestimates when artificial extinction events are imposed. The method also appears to be insensitive to trends in sampling; therefore, the counts it provides are absolute minimums. Extinctions or severe population crashes have accumulated steadily since the 1970s and 1980s, and at least 3.1% of frog species have already disappeared. Based on these data and this conservative method, the best estimate of the global grand total is roughly 200 extinctions. Consistent with previous results, frog losses are heavy in Latin America, which has been greatly affected by the pathogenic chytrid fungus Batrachochytrium dendrobatidis. Extinction rates are now four orders-of-magnitude higher than background, and at least another 6.9% of all frog species may be lost within the next century, even if there is no acceleration in the growth of environmental threats.

  8. Current extinction rates of reptiles and amphibians

    PubMed Central

    Alroy, John

    2015-01-01

    There is broad concern that a mass extinction of amphibians and reptiles is now underway. Here I apply an extremely conservative Bayesian method to estimate the number of recent amphibian and squamate extinctions in nine important tropical and subtropical regions. The data stem from a combination of museum collection databases and published site surveys. The method computes an extinction probability for each species by considering its sighting frequency and last sighting date. It infers hardly any extinction when collection dates are randomized and it provides underestimates when artificial extinction events are imposed. The method also appears to be insensitive to trends in sampling; therefore, the counts it provides are absolute minimums. Extinctions or severe population crashes have accumulated steadily since the 1970s and 1980s, and at least 3.1% of frog species have already disappeared. Based on these data and this conservative method, the best estimate of the global grand total is roughly 200 extinctions. Consistent with previous results, frog losses are heavy in Latin America, which has been greatly affected by the pathogenic chytrid fungus Batrachochytrium dendrobatidis. Extinction rates are now four orders-of-magnitude higher than background, and at least another 6.9% of all frog species may be lost within the next century, even if there is no acceleration in the growth of environmental threats. PMID:26438855

  9. Geographic range did not confer resilience to extinction in terrestrial vertebrates at the end-Triassic crisis.

    PubMed

    Dunhill, Alexander M; Wills, Matthew A

    2015-08-11

    Rates of extinction vary greatly through geological time, with losses particularly concentrated in mass extinctions. Species duration at other times varies greatly, but the reasons for this are unclear. Geographical range correlates with lineage duration amongst marine invertebrates, but it is less clear how far this generality extends to other groups in other habitats. It is also unclear whether a wide geographical distribution makes groups more likely to survive mass extinctions. Here we test for extinction selectivity amongst terrestrial vertebrates across the end-Triassic event. We demonstrate that terrestrial vertebrate clades with larger geographical ranges were more resilient to extinction than those with smaller ranges throughout the Triassic and Jurassic. However, this relationship weakened with increasing proximity to the end-Triassic mass extinction, breaking down altogether across the event itself. We demonstrate that these findings are not a function of sampling biases; a perennial issue in studies of this kind.

  10. Ca, Sr, Mo and U isotopes evidence ocean acidification and deoxygenation during the Late Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Silva-Tamayo, Juan Carlos; Payne, Jon; Wignall, Paul; Newton, Rob; Eisenhauer, Anton; Weyer, Stenfan; Neubert, Nadja; Lau, Kim; Maher, Kate; Paytan, Adina; Lehrmann, Dan; Altiner, Demir; Yu, Meiyi

    2014-05-01

    The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained. Here we use multiple isotope systems - Ca, Sr, Mo and U - measured from well dated Upper Permian- Lower Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry and the effects of ocean acidification and de-oxygenation through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing δ44/40Ca compositions, from ~-1.4‰ to -2.0‰ in the interval preceding the main extinction. These values remain low during most of the Griesbachian, to finally return to -1.4‰ in the middle Dienerian. The limestone succession from southern Turkey also displays a major decrease in the δ88/86Sr values from 0.45‰ to 0.3‰ before the extinction. These values remain low during the Griesbachian and finally increase to 0.55‰ by the middle Dienerian. The paired negative anomalies on the carbonate δ44/40Ca and δ88/86Sr suggest a decrease in the carbonate precipitation and thus an episode of ocean acidification coincident with the major biotic crisis. The Mo and U isotope records also exhibit significant rapid negative anomalies at the onset of the main extinction interval, suggesting rapid expansion of anoxic and euxinic marine bottom waters during the extinction interval. The rapidity of the isotope excursions in Mo and U suggests substantially reduced residence times of these elements in seawater relative to the modern, consistent with expectations for a time of widespread anoxia. The large C-isotope variability within Lower Triassic rocks, which is similar to that of the Lower-Middle Cambrian, may reflect biologically controlled perturbations of the oceanic carbon cycle

  11. Multiple microtektite horizons in upper Eocene marine sediments: No evidence for mass extinctions

    USGS Publications Warehouse

    Keller, G.; D'Hondt, Steven L.; Vallier, T.L.

    1983-01-01

    Microtektites have been recovered from three horizons in eight middle Eocene to middle Oligocene marine sediment sequences. Five of these occurrences are coeval and of latest Eocene age (37.5 to 38.0 million years ago); three are coeval and of early late Eocene age (38.5 to 39.5 million years ago); and three are of middle Oligocene age (31 to 32 million years ago). In addition, rare probable microtektites have been found in sediments with ages of about 36.0 to 36.5 million years. The microtektite horizon at 37.5 to 38.0 million years can be correlated with the North American tektite-strewn field, which has a fission track age (minimum) of 34 to 35 million years and a paleomagnetic age of 37.5 to 38.0 million years. There is no evidence for mass faunal extinctions at any of the microtektite horizons. Many of the distinct faunal changes that occurred in the middle Eocene to middle Oligocene can be related to the formation of the Antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large-scale dissolution of calcium carbonate and erosion, which created areally extensive hiatuses in the deep-sea sediment records. The occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle Eocene to middle Oligocene time.

  12. Impaired fear extinction in adolescent rodents: Behavioural and neural analyses.

    PubMed

    Baker, Kathryn D; Bisby, Madelyne A; Richardson, Rick

    2016-11-01

    Despite adolescence being a developmental window of vulnerability, up until very recently there were surprisingly few studies on fear extinction during this period. Here we summarise the recent work in this area, focusing on the unique behavioural and neural characteristics of fear extinction in adolescent rodents, and humans where relevant. A prominent hypothesis posits that anxiety disorders peak during late childhood/adolescence due to the non-linear maturation of the fear inhibition neural circuitry. We discuss evidence that impaired extinction retention in adolescence is due to subregions of the medial prefrontal cortex and amygdala mediating fear inhibition being underactive while other subregions that mediate fear expression are overactive. We also review work on various interventions and surprising circumstances which enhance fear extinction in adolescence. This latter work revealed that the neural correlates of extinction in adolescence are different to that in younger and older animals even when extinction retention is not impaired. This growing body of work highlights that adolescence is a unique period of development for fear inhibition. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. Extinction Mapping and Dust-to-Gas Ratios of Nearby Galaxies using LEGUS

    NASA Astrophysics Data System (ADS)

    Kahre, Lauren; Walterbos, Rene; Kim, Hwihyun; Thilker, David; Lee, Janice; LEGUS Team

    2018-01-01

    Dust is commonly used as a tracer for cold dense gas, either through IR and NIR emission maps or through extinction mapping, and dust abundance and gas metallicity are critical constraints for chemical and galaxy evolution models. Extinction mapping has been used to trace dust column densities in the Milky Way, the Magellanic Clouds, and M31. The maps for M31 use IR and NIR photometry of red giant branch stars, which is more difficult to obtain for more distant galaxies. Work by Kahre et al. (in prep) uses the extinctions derived for individual massive stars using the isochrone-matching method described by Kim et al. (2012) to generate extinction maps for these more distant galaxies.Isochrones of massive stars lie in the same location on a color-color diagram with little dependence on metallicity and luminosity class, so the extinction can be directly derived from the observed photometry. We generate extinction maps using photometry of massive stars from the Hubble Space Telescope for several of the nearly 50 galaxies observed by the Legacy Extragalactic Ultraviolet Survey (LEGUS). The derived extinction maps will allow us to correct ground-based and HST Halpha maps for extinction, and will be used to constrain changes in the dust-to-gas ratio across the galaxy sample and in different star formation, metallicity and morphological environments. Previous studies have found links between galaxy metallicity and the dust-to-gas mass ratio. We present a study of LEGUS galaxies spanning a range of distances, metallicities, and galaxy morphologies, expanding on our previous study of metal-poor dwarfs Holmberg I and II and giant spirals NGC 6503 and NGC 628. We see clear evidence for changes in the dust-to-gas mass ratio with changing metallicity. We also examine changes in the dust-to-gas mass ratio with galactocentric radius. Ultimately, we will provide constraints on the dust-to-gas mass ratio across a wide range of galaxy environments.

  14. What caused the mass extinction An extraterrestrial impact

    SciTech Connect

    Alvarez, W.; Asaro, F.

    1990-10-01

    The authors and other investigators discovered iridium in the clays that mark the sudden disappearance of dinosaurs from the fossil record. Because iridium is rare in the earth's crust but abundant in some meteorites, they concluded that a giant meteorite collided with the earth, hurling megatons of debris into the atmosphere. This paper describes and discusses the accumulating evidence that suggests an asteroid or comet caused the Cretaceous extinction.

  15. Impact ejecta layer from the mid-Devonian: possible connection to global mass extinctions.

    PubMed

    Ellwood, Brooks B; Benoist, Stephen L; El Hassani, Ahmed; Wheeler, Christopher; Crick, Rex E

    2003-06-13

    We have found evidence for a bolide impacting Earth in the mid-Devonian ( approximately 380 million years ago), including high concentrations of shocked quartz, Ni, Cr, As, V, and Co anomalies; a large negative carbon isotope shift (-9 per mil); and microspherules and microcrysts at Jebel Mech Irdane in the Anti Atlas desert near Rissani, Morocco. This impact is important because it is coincident with a major global extinction event (Kacák/otomari event), suggesting a possible cause-and-effect relation between the impact and the extinction. The result may represent the extinction of as many as 40% of all living marine animal genera.

  16. Impact Ejecta Layer from the Mid-Devonian: Possible Connection to Global Mass Extinctions

    NASA Astrophysics Data System (ADS)

    Ellwood, Brooks B.; Benoist, Stephen L.; Hassani, Ahmed El; Wheeler, Christopher; Crick, Rex E.

    2003-06-01

    We have found evidence for a bolide impacting Earth in the mid-Devonian (~380 million years ago), including high concentrations of shocked quartz, Ni, Cr, As, V, and Co anomalies; a large negative carbon isotope shift (-9 per mil); and microspherules and microcrysts at Jebel Mech Irdane in the Anti Atlas desert near Rissani, Morocco. This impact is important because it is coincident with a major global extinction event (Kacák/otomari event), suggesting a possible cause-and-effect relation between the impact and the extinction. The result may represent the extinction of as many as 40% of all living marine animal genera.

  17. Comparison of the ages of large-body impacts, flood-basalt eruptions, ocean-anoxic events and extinctions over the last 260 million years: a statistical study

    NASA Astrophysics Data System (ADS)

    Rampino, Michael R.; Caldeira, Ken

    2018-03-01

    Many studies have linked mass extinction events with the catastrophic effects of large-body impacts and flood-basalt eruptions, sometimes as competing explanations. We find that the ages of at least 10 out of a total of 11 documented extinction events over the last 260 Myr (12 out of 13 if we include two lesser extinction events) coincide, within errors, with the best-known ages of either a large impact crater (≥70 km diameter) or a continental flood-basalt eruption. The null hypothesis that this could occur by chance can be rejected with very high confidence (>99.999%). The ages of large impact craters correlate with recognized extinction events at 36 (two impacts), 66, 145 and 215 Myr ago (and possibly an event at 168 Myr ago), and the ages of continental flood basalts correlate with extinctions at 66, 94, 116, 183, 201, 252 and 259 Myr ago (and possibly at 133 Myr ago). Furthermore, at least 7 periods of widespread anoxia in the oceans of the last 260 Myr coincide with the ages of flood-basalt eruptions (with 99.999% confidence), and are coeval with extinctions, suggesting causal connections. These statistical relationships argue that most mass extinction events are related to climatic catastrophes produced by the largest impacts and large-volume continental flood-basalt eruptions.

  18. Recovery of Carbonate Ecosystems Following the End-Triassic Mass Extinction: Insights from Mercury Anomalies and Their Relationship to the Central Atlantic Magmatic Province

    NASA Astrophysics Data System (ADS)

    Corsetti, F. A.; Thibodeau, A. M.; Ritterbush, K. A.; West, A. J.; Yager, J. A.; Ibarra, Y.; Bottjer, D. J.; Berelson, W.; Bergquist, B. A.

    2015-12-01

    Recent high-resolution age dating demonstrates that the end-Triassic mass extinction overlapped with the eruption of the Central Atlantic Magmatic Province (CAMP), and the release of CO2 and other volatiles to the atmosphere has been implicated in the extinction. Given the potentially massive release of CO2, ocean acidification is commonly considered a factor in the extinction and the collapse of shallow marine carbonate ecosystems. However, the timing of global marine biotic recovery versus the CAMP eruptions is more uncertain. Here, we use Hg concentrations and Hg/TOC ratios as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. In Triassic-Jurassic strata, Muller Canyon, Nevada, Hg and Hg/TOC levels are low prior to the extinction, rise sharply in the extinction interval, peak just prior to the appearance of the first Jurassic ammonite, and remain above background in association with a depauperate (low diversity) earliest Jurassic fauna. The return of Hg to pre-extinction levels is associated with a significant pelagic and benthic faunal recovery. We conclude that significant biotic recovery did not begin until CAMP eruptions ceased. Furthermore, the initial benthic recovery in the Muller Canyon section involves the expansion of a siliceous sponge-dominated ecosystem across shallow marine environments, a feature now known from other sections around the world (e.g., Peru, Morocco, Austria, etc.). Carbonate dominated benthic ecosystems (heralded by the return of abundant corals and other skeletal carbonates) did not recover for ~1 million years following the last eruption of CAMP, longer than the typical duration considered for ocean acidification events, implying other factors may have played a role in carbonate ecosystem dynamics after the extinction.

  19. Extinction risk is most acute for the world's largest and smallest vertebrates.

    PubMed

    Ripple, William J; Wolf, Christopher; Newsome, Thomas M; Hoffmann, Michael; Wirsing, Aaron J; McCauley, Douglas J

    2017-10-03

    Extinction risk in vertebrates has been linked to large body size, but this putative relationship has only been explored for select taxa, with variable results. Using a newly assembled and taxonomically expansive database, we analyzed the relationships between extinction risk and body mass (27,647 species) and between extinction risk and range size (21,294 species) for vertebrates across six main classes. We found that the probability of being threatened was positively and significantly related to body mass for birds, cartilaginous fishes, and mammals. Bimodal relationships were evident for amphibians, reptiles, and bony fishes. Most importantly, a bimodal relationship was found across all vertebrates such that extinction risk changes around a body mass breakpoint of 0.035 kg, indicating that the lightest and heaviest vertebrates have elevated extinction risk. We also found range size to be an important predictor of the probability of being threatened, with strong negative relationships across nearly all taxa. A review of the drivers of extinction risk revealed that the heaviest vertebrates are most threatened by direct killing by humans. By contrast, the lightest vertebrates are most threatened by habitat loss and modification stemming especially from pollution, agricultural cropping, and logging. Our results offer insight into halting the ongoing wave of vertebrate extinctions by revealing the vulnerability of large and small taxa, and identifying size-specific threats. Moreover, they indicate that, without intervention, anthropogenic activities will soon precipitate a double truncation of the size distribution of the world's vertebrates, fundamentally reordering the structure of life on our planet.

  20. Post-Learning Sleep Transiently Boosts Context Specific Operant Extinction Memory.

    PubMed

    Borquez, Margarita; Contreras, María P; Vivaldi, Ennio; Born, Jan; Inostroza, Marion

    2017-01-01

    Operant extinction is learning to supress a previously rewarded behavior. It is known to be strongly associated with the specific context in which it was acquired, which limits the therapeutic use of operant extinction in behavioral treatments, e.g., of addiction. We examined whether sleep influences contextual memory of operant extinction over time, using two different recall tests (Recent and Remote). Rats were trained in an operant conditioning task (lever press) in context A, then underwent extinction training in context B, followed by a 3-h retention period that contained either spontaneous morning sleep, morning sleep deprivation, or spontaneous evening wakefulness. A recall test was performed either immediately after the 3-h experimental retention period (Recent recall) or after 48 h (Remote), in the extinction context B and in a novel context C. The two main findings were: (i) at the Recent recall test, sleep in comparison with sleep deprivation and spontaneous wakefulness enhanced extinction memory but, only in the extinction context B; (ii) at the Remote recall, extinction performance after sleep was enhanced in both contexts B and C to an extent comparable to levels at Recent recall in context B. Interestingly, extinction performance at Remote recall was also improved in the sleep deprivation groups in both contexts, with no difference to performance in the sleep group. Our results suggest that 3 h of post-learning sleep transiently facilitate the context specificity of operant extinction at a Recent recall. However, the improvement and contextual generalization of operant extinction memory observed in the long-term, i.e., after 48 h, does not require immediate post-learning sleep.

  1. Global Evidence for an End-Permian Mass Extinction Event

    NASA Astrophysics Data System (ADS)

    Becker, L.; Nicholson, C.; Poreda, R.; Basu, A.; Acampo, A.

    2003-04-01

    We will present the global evidence for a Permian-Triassic impact event and re-examine some of the structural, seismic, gravity and well data for a proposed impact crater, the Bedout High, offshore northwestern Australia (Gorter, PESA News pp. 33--34, 1996). Gorter (1996) speculates that the Bedout High is the uplifted core (30 km) of a circular feature, some 220 km across, formed by the impact of a large bolide (comet or asteroid) with the earth near the end-Permian (K-Ar dating of volcanics ˜253 +/- 5 Ma). Accepting a possible impact origin for the Bedout structure, with the indicated dimensions, would have had profound effects on global climate and significant changes in lithotratigraphic, biostratigraphic and chemo-stratigraphic indicators as seen in several Permian-Triassic locations worldwide. Evidence for an impact of extraterrestrial origin is based upon several impact tracers including shocked metamorphosed grains, productivity collapse, helium-3, Mossbauer spectroscopy on nanophase Fe material, noble gases in magnetic fines and fullerenes with trapped noble gases from some end-Permian sites. These findings suggest that the Bedout structure and a possible newly discovered (˜100 km) secondary crater may be good candidates for an oceanic/continental impact(s) at the end Permian, triggering the most severe mass extinction in the history of life on the Earth.

  2. IODP-ICDP Expedition 364: Drilling the Chicxulub impact crater to understand planetary evolution and mass extinction

    NASA Astrophysics Data System (ADS)

    Gulick, S. P. S.; Morgan, J. V.

    2017-12-01

    The most recent of Earth's five largest mass extinction events occurred 66 Ma, coeval with the impact of a 12 km asteroid, striking at 60 degrees into what is today the Yucatán Peninsula, México, producing the 200 km-wide Chicxulub crater. This impact, by some estimations, drove the extinction of 75% of life on Earth at the genus level. The mass extinction event marks the boundary between the Cretaceous and Paleogene. Proposed kill mechanisms include thermal effects caused by the reentry of fast ejecta into Earth's atmosphere, dust and sulfate aerosols reducing Earth's solar insolation, ocean acidification, and metal toxicity due to the chemical make-up of the impactor. The magnitude and duration of these processes is still debated, and further evaluation of the proposed kill mechanisms requires an understanding of the mechanics of the Chicxulub impact as well as the resulting global environmental perturbations. In April and May 2016, the International Ocean Discovery Program, with co-funding from the International Continental Scientific Drilling Program, successfully cored into the Chicxulub impact crater with nearly 100% recovery. These cores include the first-ever samples of the transition from an intact peak ring through post-impact sediments. A peak ring is a discontinuous ring of mountains observed within the central basin of all large impact craters on rocky planets. Newly drilled cores include the uplifted target rocks, melt-rich impactites, hydrothermal deposits, a possible settling layer, and the resumption of carbonate sedimentation. The discovery that Chicxulub's peak ring consists of largely granitic crust uplifted by 10 km calibrates impact models and allows for observation of impact processes. At the top of the peak ring, the K-Pg boundary deposit includes a impactite sequence 130 m thick deposited by processes that range from minutes to likely years post-impact. This sequence is then overprinted by hydrothermal processes that lasted at least 100s

  3. Arthropods and the Current Great Mass Extinction: Effective Themes to Decrease Arthropod Fear and Disgust and Increase Positive Environmental Beliefs in Children?

    ERIC Educational Resources Information Center

    Wagler, Amy; Wagler, Ron

    2014-01-01

    Earth is experiencing a great mass extinction (GME) that has been caused by the environmentally destructive activities of humans. This GME is having and will have profound effects on Earth's biodiversity if environmental sustainability is not reached. Activities and curriculum tools have been developed to assist teachers in integrating the current…

  4. Impact Theory of Mass Extinctions and the Invertebrate Fossil Record

    NASA Astrophysics Data System (ADS)

    Alvarez, Walter; Kauffman, Erle G.; Surlyk, Finn; Alvarez, Luis W.; Asaro, Frank; Michel, Helen V.

    1984-03-01

    There is much evidence that the Cretaceous-Tertiary boundary was marked by a massive meteorite impact. Theoretical consideration of the consequences of such an impact predicts sharp extinctions in many groups of animals precisely at the boundary. Paleontological data clearly show gradual declines in diversity over the last 1 to 10 million years in various invertebrate groups. Reexamination of data from careful studies of the best sections shows that, in addition to undergoing the decline, four groups (ammonites, cheilostomate bryozoans, brachiopods, and bivalves) were affected by sudden truncations precisely at the iridium anomaly that marks the boundary. The paleontological record thus bears witness to terminal-Cretaceous extinctions on two time scales: a slow decline unrelated to the impact and a sharp truncation synchronous with and probably caused by the impact.

  5. Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction

    NASA Astrophysics Data System (ADS)

    Pilet, S.; Müntener, O.; Jean, G.; Schoene, B.; Schaltegger, U.

    2016-12-01

    The temporal coincidence between LIPs and mass extinctions has led many to pose a causal relationship between the two. However, there is still no consensus on a mechanistic model that explains how magmatism leads to the turnover of terrestrial and marine plants, invertebrates and vertebrates. Here, we present a synthesis of stratigraphic constraints on the Triassic-Jurassic and Pliensbachian-Toarcian boundaries combined with geochronological data demonstrating that these biotic crises are both associated with rapid change from an initial cool period to greenhouse conditions. As current hypothesis for LIPs seems unable to produce these successive climatic changes, we evaluate an alternative suggesting that the initial cooling could be due to gas release during the initial thermal erosion of the cratonic lithosphere due to emplacement of the CAMP and Karoo-Ferrar volcanic provinces. Karoo and CAMP areas were underlain by thick lithosphere (>200 km) prior to continental break up. Even in presence of abnormal potential mantle temperature, the presence of thick lithosphere excludes significant melting of the asthenospheric mantle without initial stage of thermal erosion of the cratonic lithosphere. Various studies on Kaapvaal craton have shown that sulfide minerals are enclosed in the basal part of the cratonic lithosphere. We argue that initial gas emission was dominated by sulfur liberated from sulfide-bearing cratonic lithosphere causing global cooling and eustatic regression, which was followed by warming/transgression associated with the progressive increase of CO2 in the atmosphere associated to LIPs emission. We suggest that the nature of the underlying lithosphere during large LIP eruption exerts an important control on the consequences at the Earth's surface. This model offers an explanation for why LIPs erupted through oceanic lithosphere are not associated with climatic and biotic crises comparable to LIPs emitted through cratonic lithosphere.

  6. Smoking cue reactivity across massed extinction trials: negative affect and gender effects.

    PubMed

    Collins, Bradley N; Nair, Uma S; Komaroff, Eugene

    2011-04-01

    Designing and implementing cue exposure procedures to treat nicotine dependence remains a challenge. This study tested the hypothesis that gender and negative affect (NA) influence changes in smoking urge over time using data from a pilot project testing the feasibility of massed extinction procedures. Forty-three smokers and ex-smokers completed the behavioral laboratory procedures. All participants were over 17 years old, smoked at least 10 cigarettes daily over the last year (or the year prior to quitting) and had expired CO below 10 ppm at the beginning of the ~4-hour session. After informed consent, participants completed 45 min of baseline assessments, and then completed a series of 12 identical, 5-minute exposure trials with inter-trial breaks. Smoking cues included visual, tactile, and olfactory cues with a lit cigarette, in addition to smoking-related motor behaviors without smoking. After each trial, participants reported urge and negative affect (NA). Logistic growth curve models supported the hypothesis that across trials, participants would demonstrate an initial linear increase followed by a decrease in smoking urge (quadratic effect). Data supported hypothesized gender, NA, and gender×NA effects. Significant linear increases in urge were observed among high and low NA males, but not among females in either NA subgroup. A differential quadratic effect showed a significant decrease in urge for the low NA subgroup, but a non-significant decrease in urge in the high NA group. This is the first study to demonstrate gender differences and the effects of NA on the extinction process using a smoking cue exposure paradigm. Results could guide future cue reactivity research and exposure interventions for nicotine dependence. Copyright © 2010 Elsevier B.V. All rights reserved.

  7. Hippocampus NMDA receptors selectively mediate latent extinction of place learning.

    PubMed

    Goodman, Jarid; Gabriele, Amanda; Packard, Mark G

    2016-09-01

    effective at extinguishing memory in the place learning task. In addition, intra-hippocampal AP5 (7.5 µg) impaired latent extinction, but not response extinction, suggesting that hippocampal NMDA receptors are selectively involved in latent extinction. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  8. Characterization of Diesel Soot Aggregates by Scattering and Extinction Methods

    NASA Astrophysics Data System (ADS)

    Kamimoto, Takeyuki

    2006-07-01

    Characteristics of diesel soot particles sampled from diesel exhaust of a common-rail turbo-charged diesel engine are quantified by scattering and extinction diagnostics using newly build two laser-based instruments. The radius of gyration representing the aggregates size is measured by the angular distribution of scattering intensity, while the soot mass concentration is measured by a two-wavelength extinction method. An approach to estimate the refractive index of diesel soot by an analysis of the extinction and scattering data using an aggregates scattering theory is proposed.

  9. Mass extinction of ocean organisms at the Paleozoic-Mesozoic boundary: Effects and causes

    NASA Astrophysics Data System (ADS)

    Barash, M. S.

    2012-04-01

    At the end of the Permian, at the boundary between the Paleozoic and Mesozoic (251.0 ± 0.4 Ma), the largest mass extinction of organisms on the Earth occurred. Up to 96% of the species of marine invertebrates and ˜70% of the terrestrial vertebrates died off. A lot of factors were suggested and substantiated to explain this mass mortality, such as the disappearance of environmental niches in the course of the amalgamation of the continental plates into Pangea, sea level fluctuations, anoxia, an elevated CO2 content, H2S intoxication, volcanism, methane discharge from gas-hydrates, climate changes, impact events (collisions with large asteroids), or combinations of many of these reasons. Some of these factors are in subordination to others, while others are independent. Almost all of these factors developed relatively slowly and could not cause the sudden mass mortality of organisms globally. It could have happened when large asteroids, whose craters have been discovered lately, fell to the Earth. It is suggested that the impact events "finished off" the already suppressed biota. A simultaneous change in many of the factors responsible for the biodiversity, including those not connected in a cause-and-effect relationship, proves the existence of a common extrater-restrial cause that affected both the changes in the internal and external geospheres and the activation of asteroid attacks (the Sun's transit of spiral arms of our galaxy, the Sun's oscillations perpendicularly to the galactic plane, etc).

  10. Mercury anomaly, Deccan volcanism and the end-Cretaceous mass extinction

    NASA Astrophysics Data System (ADS)

    Font, Eric; Adatte, Thierry; Nobrega Sial, Alcides; Drude de Lacerda, Luiz; Keller, Gerta; Punekar, Jahnavi

    2016-04-01

    The contribution of the Deccan Traps volcanism in the Cretaceous-Palaeogene (KPg) crisis is still a matter of debate. Particularly, the global geochemical effects of Deccan volcanism in the marine sedimentary record are still poorly resolved. Here, we investigate the mercury (Hg) content of the Bidart (France) section, where an interval of low magnetic susceptibility (MS) located just below the KPg boundary was hypothesized to result from paleoenvironmental perturbations linked to paroxysmal Deccan phase-2. Results show mercury concentrations over two orders of magnitude higher from ~80 cm below up to ~50 cm above the KPg boundary (max. 46.6 ppb) and coincident with the low MS interval. Increase in Hg contents shows no correlation with clay or total organic carbon contents, suggesting that the mercury anomalies resulted from higher input of atmospheric Hg species into the marine realm, rather than organic matter scavenging and/or increased run-off. The Hg anomalies correlate with high shell fragmentation and dissolution effects in planktic foraminifera suggesting correlative changes in marine biodiversity. This discovery represents an unprecedented piece of evidence of the nature and importance of the Deccan-related environmental changes at the onset of the KPg mass extinction. Funded by IDL (FCT UID/GEO/50019/2013)

  11. Testing for variation in taxonomic extinction probabilities: a suggested methodology and some results

    USGS Publications Warehouse

    Conroy, M.J.; Nichols, J.D.

    1984-01-01

    Several important questions in evolutionary biology and paleobiology involve sources of variation in extinction rates. In all cases of which we are aware, extinction rates have been estimated from data in which the probability that an observation (e.g., a fossil taxon) will occur is related both to extinction rates and to what we term encounter probabilities. Any statistical method for analyzing fossil data should at a minimum permit separate inferences on these two components. We develop a method for estimating taxonomic extinction rates from stratigraphic range data and for testing hypotheses about variability in these rates. We use this method to estimate extinction rates and to test the hypothesis of constant extinction rates for several sets of stratigraphic range data. The results of our tests support the hypothesis that extinction rates varied over the geologic time periods examined. We also present a test that can be used to identify periods of high or low extinction probabilities and provide an example using Phanerozoic invertebrate data. Extinction rates should be analyzed using stochastic models, in which it is recognized that stratigraphic samples are random varlates and that sampling is imperfect

  12. Extinction risk is most acute for the world’s largest and smallest vertebrates

    PubMed Central

    Ripple, William J.; Wolf, Christopher; Newsome, Thomas M.; Hoffmann, Michael; Wirsing, Aaron J.; McCauley, Douglas J.

    2017-01-01

    Extinction risk in vertebrates has been linked to large body size, but this putative relationship has only been explored for select taxa, with variable results. Using a newly assembled and taxonomically expansive database, we analyzed the relationships between extinction risk and body mass (27,647 species) and between extinction risk and range size (21,294 species) for vertebrates across six main classes. We found that the probability of being threatened was positively and significantly related to body mass for birds, cartilaginous fishes, and mammals. Bimodal relationships were evident for amphibians, reptiles, and bony fishes. Most importantly, a bimodal relationship was found across all vertebrates such that extinction risk changes around a body mass breakpoint of 0.035 kg, indicating that the lightest and heaviest vertebrates have elevated extinction risk. We also found range size to be an important predictor of the probability of being threatened, with strong negative relationships across nearly all taxa. A review of the drivers of extinction risk revealed that the heaviest vertebrates are most threatened by direct killing by humans. By contrast, the lightest vertebrates are most threatened by habitat loss and modification stemming especially from pollution, agricultural cropping, and logging. Our results offer insight into halting the ongoing wave of vertebrate extinctions by revealing the vulnerability of large and small taxa, and identifying size-specific threats. Moreover, they indicate that, without intervention, anthropogenic activities will soon precipitate a double truncation of the size distribution of the world’s vertebrates, fundamentally reordering the structure of life on our planet. PMID:28923917

  13. The Butterflies of Barro Colorado Island, Panama: Local Extinction since the 1930s

    PubMed Central

    Basset, Yves; Barrios, Héctor; Segar, Simon; Srygley, Robert B.; Aiello, Annette; Warren, Andrew D.; Delgado, Francisco; Coronado, James; Lezcano, Jorge; Arizala, Stephany; Rivera, Marleny; Perez, Filonila; Bobadilla, Ricardo; Lopez, Yacksecari; Ramirez, José Alejandro

    2015-01-01

    Few data are available about the regional or local extinction of tropical butterfly species. When confirmed, local extinction was often due to the loss of host-plant species. We used published lists and recent monitoring programs to evaluate changes in butterfly composition on Barro Colorado Island (BCI, Panama) between an old (1923–1943) and a recent (1993–2013) period. Although 601 butterfly species have been recorded from BCI during the 1923–2013 period, we estimate that 390 species are currently breeding on the island, including 34 cryptic species, currently only known by their DNA Barcode Index Number. Twenty-three butterfly species that were considered abundant during the old period could not be collected during the recent period, despite a much higher sampling effort in recent times. We consider these species locally extinct from BCI and they conservatively represent 6% of the estimated local pool of resident species. Extinct species represent distant phylogenetic branches and several families. The butterfly traits most likely to influence the probability of extinction were host growth form, wing size and host specificity, independently of the phylogenetic relationships among butterfly species. On BCI, most likely candidates for extinction were small hesperiids feeding on herbs (35% of extinct species). However, contrary to our working hypothesis, extinction of these species on BCI cannot be attributed to loss of host plants. In most cases these host plants remain extant, but they probably subsist at lower or more fragmented densities. Coupled with low dispersal power, this reduced availability of host plants has probably caused the local extinction of some butterfly species. Many more bird than butterfly species have been lost from BCI recently, confirming that small preserves may be far more effective at conserving invertebrates than vertebrates and, therefore, should not necessarily be neglected from a conservation viewpoint. PMID:26305111

  14. The Butterflies of Barro Colorado Island, Panama: Local Extinction since the 1930s.

    PubMed

    Basset, Yves; Barrios, Héctor; Segar, Simon; Srygley, Robert B; Aiello, Annette; Warren, Andrew D; Delgado, Francisco; Coronado, James; Lezcano, Jorge; Arizala, Stephany; Rivera, Marleny; Perez, Filonila; Bobadilla, Ricardo; Lopez, Yacksecari; Ramirez, José Alejandro

    2015-01-01

    Few data are available about the regional or local extinction of tropical butterfly species. When confirmed, local extinction was often due to the loss of host-plant species. We used published lists and recent monitoring programs to evaluate changes in butterfly composition on Barro Colorado Island (BCI, Panama) between an old (1923-1943) and a recent (1993-2013) period. Although 601 butterfly species have been recorded from BCI during the 1923-2013 period, we estimate that 390 species are currently breeding on the island, including 34 cryptic species, currently only known by their DNA Barcode Index Number. Twenty-three butterfly species that were considered abundant during the old period could not be collected during the recent period, despite a much higher sampling effort in recent times. We consider these species locally extinct from BCI and they conservatively represent 6% of the estimated local pool of resident species. Extinct species represent distant phylogenetic branches and several families. The butterfly traits most likely to influence the probability of extinction were host growth form, wing size and host specificity, independently of the phylogenetic relationships among butterfly species. On BCI, most likely candidates for extinction were small hesperiids feeding on herbs (35% of extinct species). However, contrary to our working hypothesis, extinction of these species on BCI cannot be attributed to loss of host plants. In most cases these host plants remain extant, but they probably subsist at lower or more fragmented densities. Coupled with low dispersal power, this reduced availability of host plants has probably caused the local extinction of some butterfly species. Many more bird than butterfly species have been lost from BCI recently, confirming that small preserves may be far more effective at conserving invertebrates than vertebrates and, therefore, should not necessarily be neglected from a conservation viewpoint.

  15. Source apportionment of PM2.5 light extinction in an urban atmosphere in China.

    PubMed

    Lan, Zijuan; Zhang, Bin; Huang, Xiaofeng; Zhu, Qiao; Yuan, Jinfeng; Zeng, Liwu; Hu, Min; He, Lingyan

    2018-01-01

    Haze in China is primarily caused by high pollution of atmospheric fine particulates (PM 2.5 ). However, the detailed source structures of PM 2.5 light extinction have not been well established, especially for the roles of various organic aerosols, which makes haze management lack specified targets. This study obtained the mass concentrations of the chemical compositions and the light extinction coefficients of fine particles in the winter in Dongguan, Guangdong Province, using high time resolution aerosol observation instruments. We combined the positive matrix factor (PMF) analysis model of organic aerosols and the multiple linear regression method to establish a quantitative relationship model between the main chemical components, in particular the different sources of organic aerosols and the extinction coefficients of fine particles with a high goodness of fit (R 2 =0.953). The results show that the contribution rates of ammonium sulphate, ammonium nitrate, biomass burning organic aerosol (BBOA), secondary organic aerosol (SOA) and black carbon (BC) were 48.1%, 20.7%, 15.0%, 10.6%, and 5.6%, respectively. It can be seen that the contribution of the secondary aerosols is much higher than that of the primary aerosols (79.4% versus 20.6%) and are a major factor in the visibility decline. BBOA is found to have a high visibility destroying potential, with a high mass extinction coefficient, and was the largest contributor during some high pollution periods. A more detailed analysis indicates that the contribution of the enhanced absorption caused by BC mixing state was approximately 37.7% of the total particle absorption and should not be neglected. Copyright © 2017. Published by Elsevier B.V.

  16. Chemical antipredator defence is linked to higher extinction risk

    PubMed Central

    2016-01-01

    Many attributes of species may be linked to contemporary extinction risk, though some such traits remain untested despite suggestions that they may be important. Here, I test whether a trait associated with higher background extinction rates, chemical antipredator defence, is also associated with current extinction risk, using amphibians as a model system—a group facing global population declines. I find that chemically defended species are approximately 60% more likely to be threatened than species without chemical defence, although the severity of the contemporary extinction risk may not relate to chemical defence. The results confirm that background and contemporary extinction rates can be predicted from the same traits, at least in certain cases. This suggests that associations between extinction risk and phenotypic traits can be temporally stable over long periods. The results also provide novel insights into the relevance of antipredator defences for species subject to conservation concerns. PMID:28018657

  17. NEW EXTINCTION AND MASS ESTIMATES FROM OPTICAL PHOTOMETRY OF THE VERY LOW MASS BROWN DWARF COMPANION CT CHAMAELEONTIS B WITH THE MAGELLAN AO SYSTEM

    SciTech Connect

    Wu, Ya-Lin; Close, Laird M.; Males, Jared R.

    We used the Magellan adaptive optics system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r', i', z', and Y{sub S}. With our new photometry and T {sub eff} ∼ 2500 K derived from the shape of its K-band spectrum, we find that CT Cha B has A{sub V} = 3.4 ± 1.1 mag, and a mass of 14-24 M{sub J} according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates thatmore » the companion has significant Hα emission and a mass accretion rate ∼6 × 10{sup –10} M {sub ☉} yr{sup –1}, similar to some substellar companions. Proper motion analysis shows that another point source within 2'' of CT Cha A is not physical. This paper demonstrates how visible wavelength adaptive optics photometry (r', i', z', Y{sub S}) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions.« less

  18. New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Lin; Close, Laird M.; Males, Jared R.; Barman, Travis S.; Morzinski, Katie M.; Follette, Katherine B.; Bailey, Vanessa; Rodigas, Timothy J.; Hinz, Philip; Puglisi, Alfio; Xompero, Marco; Briguglio, Runa

    2015-03-01

    We used the Magellan adaptive optics system and its VisAO CCD camera to image the young low mass brown dwarf companion CT Chamaeleontis B for the first time at visible wavelengths. We detect it at r', i', z', and YS . With our new photometry and T eff ~ 2500 K derived from the shape of its K-band spectrum, we find that CT Cha B has AV = 3.4 ± 1.1 mag, and a mass of 14-24 MJ according to the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r' detection indicates that the companion has significant Hα emission and a mass accretion rate ~6 × 10-10 M ⊙ yr-1, similar to some substellar companions. Proper motion analysis shows that another point source within 2'' of CT Cha A is not physical. This paper demonstrates how visible wavelength adaptive optics photometry (r', i', z', YS ) allows for a better estimate of extinction, luminosity, and mass accretion rate of young substellar companions. This paper includes data gathered with the 6.5 m Magellan Clay Telescope at Las Campanas Observatory, Chile.

  19. Boron isotopes in brachiopods during the end-Permian mass extinction: constraints on pH evolution and seawater chemistry

    NASA Astrophysics Data System (ADS)

    Jurikova, Hana; Gutjahr, Marcus; Liebetrau, Volker; Brand, Uwe; Posenato, Renato; Garbelli, Claudio; Angiolini, Lucia; Eisenhauer, Anton

    2017-04-01

    The global biogeochemical cycling of carbon is fundamental for life on Earth with the ocean playing a key role as the largest and dynamically evolving CO2 reservoir. The boron isotope composition (commonly expressed in δ11B) of marine calcium carbonate is considered to be one of the most reliable paleo-pH proxies, potentially enabling us to reconstruct past ocean pH changes and understand carbon cycle perturbations along Earth's geological record (e.g. Foster et al., 2008; Clarkson et al., 2015). Brachiopods present an advantageous and largely underutilised archive for Phanerozoic carbon cycle reconstructions considering their high abundance in the geological record and its origin dating back to the early Cambrian. Moreover, their shell made of low-magnesium calcite makes these marine calcifiers more resistant to post-depositional diagenetic alteration of primary chemical signals. We have investigated the δ11B using MC-ICP-MS (Neptune Plus) and B/Ca and other elemental ratios (Mg/Ca, Sr/Ca, Al/Ca, Li/Ca, Ba/Ca, Na/Ca and Fe/Ca) using ICP-MS-Quadrupole (Agilent 7500cx) from the same specimens in pristine brachiopod shells from two sections from northern Italy during the Late Permian. These sections cover the δ13C excursion in excess of ˜4 ‰ (Brand et al., 2012) and are associated with major climate and environmental perturbations that lead to the mass extinction event at the Permian-Triassic boundary. Particular emphasis will be placed on the implications of our new paleo-pH estimates on the seawater chemistry during the Late Permian. Brand, U., Posenato, R., Came, R., Affek, H., Angiolini, L., Azmy, K. and Farabegoli, E.: The end-Permian mass extinction: A rapid volcanic CO2 and CH4-climatic catastrophe, Chemical Geology 323, 121-144, doi:10.1016/j.chemgeo.2012.06.015, 2012. Clarkson, M.O., Kasemann, S.A., Wood, R.A., Lenton, T.M., Daines, S.J., Richoz, S., Ohnemueller, F., Meixner, A., Poulton, S.W. and Tipper, E.T.: Ocean acidification and the Permo

  20. Evolution and Extinction Dynamics in Rugged Fitness Landscapes

    NASA Astrophysics Data System (ADS)

    Sibani, Paolo; Brandt, Michael; Alstrøm, Preben

    After an introductory section summarizing the paleontological data and some of their theoretical descriptions, we describe the "reset" model and its (in part analytically soluble) mean field version, which have been briefly introduced in Letters.1,2 Macroevolution is considered as a problem of stochastic dynamics in a system with many competing agents. Evolutionary events (speciations and extinctions) are triggered by fitness records found by random exploration of the agents' fitness landscapes. As a consequence, the average fitness in the system increases logarithmically with time, while the rate of extinction steadily decreases. This non-stationary dynamics is studied by numerical simulations and, in a simpler mean field version, analytically. We also consider the effect of externally added "mass" extinctions. The predictions for various quantities of paleontological interest (life-time distribution, distribution of event sizes and behavior of the rate of extinction) are robust and in good agreement with available data.

  1. Fossil Worm Burrows Reveal Very Early Terrestrial Animal Activity and Shed Light on Trophic Resources after the End-Cretaceous Mass Extinction

    PubMed Central

    Chin, Karen; Pearson, Dean; Ekdale, A. A.

    2013-01-01

    The widespread mass extinctions at the end of the Cretaceous caused world-wide disruption of ecosystems, and faunal responses to the one-two punch of severe environmental perturbation and ecosystem collapse are still unclear. Here we report the discovery of in situ terrestrial fossil burrows from just above the impact-defined Cretaceous-Paleogene (K/Pg) boundary in southwestern North Dakota. The crisscrossing networks of horizontal burrows occur at the interface of a lignitic coal and silty sandstone, and reveal intense faunal activity within centimeters of the boundary clay. Estimated rates of sedimentation and coal formation suggest that the burrows were made less than ten thousand years after the end-Cretaceous impact. The burrow characteristics are most consistent with burrows of extant earthworms. Moreover, the burrowing and detritivorous habits of these annelids fit models that predict the trophic and sheltering lifestyles of terrestrial animals that survived the K/Pg extinction event. In turn, such detritus-eaters would have played a critical role in supporting secondary consumers. Thus, some of the carnivorous vertebrates that radiated after the K/Pg extinction may owe their evolutionary success to thriving populations of earthworms. PMID:23951041

  2. Tetrapod distribution and temperature rise during the Permian–Triassic mass extinction

    PubMed Central

    2018-01-01

    The Permian–Triassic mass extinction (PTME) had an enormous impact on life in three ways: by substantially reducing diversity, by reshuffling the composition of ecosystems and by expelling life from the tropics following episodes of intense global warming. But was there really an ‘equatorial tetrapod gap', and how long did it last? Here, we consider both skeletal and footprint data, and find a more complex pattern: (i) tetrapods were distributed both at high and low latitudes during this time; (ii) there was a clear geographic disjunction through the PTME, with tetrapod distribution shifting 10–15° poleward; and (iii) there was a rapid expansion phase across the whole of Pangea following the PTME. These changes are consistent with a model of generalized migration of tetrapods to higher latitudinal, cooler regions, to escape from the superhot equatorial climate in the earliest Triassic, but the effect was shorter in time scale, and not as pronounced as had been proposed. In the recovery phase following the PTME, this episode of forced range expansion also appears to have promoted the emergence and radiation of entirely new groups, such as the archosaurs, including the dinosaurs. PMID:29321300

  3. Tetrapod distribution and temperature rise during the Permian-Triassic mass extinction.

    PubMed

    Bernardi, Massimo; Petti, Fabio Massimo; Benton, Michael J

    2018-01-10

    The Permian-Triassic mass extinction (PTME) had an enormous impact on life in three ways: by substantially reducing diversity, by reshuffling the composition of ecosystems and by expelling life from the tropics following episodes of intense global warming. But was there really an 'equatorial tetrapod gap', and how long did it last? Here, we consider both skeletal and footprint data, and find a more complex pattern: (i) tetrapods were distributed both at high and low latitudes during this time; (ii) there was a clear geographic disjunction through the PTME, with tetrapod distribution shifting 10-15° poleward; and (iii) there was a rapid expansion phase across the whole of Pangea following the PTME. These changes are consistent with a model of generalized migration of tetrapods to higher latitudinal, cooler regions, to escape from the superhot equatorial climate in the earliest Triassic, but the effect was shorter in time scale, and not as pronounced as had been proposed. In the recovery phase following the PTME, this episode of forced range expansion also appears to have promoted the emergence and radiation of entirely new groups, such as the archosaurs, including the dinosaurs. © 2018 The Authors.

  4. The interaction of the cretaceous-tertiary extinction bolide with the atmosphere, ocean, and solid earth

    NASA Technical Reports Server (NTRS)

    Okeefe, J. D.; Ahrens, T. J.

    1981-01-01

    A number of investigations, including those reported by Orth et al. (1981), have provided physical evidence for the impact of an extraterrestrial object on earth 65 million years ago. This time corresponds to the end of the cretaceous period. This impact could, therefore, be responsible for the observed extinction of biological species at the end of the Mesozoic era. Among the species becoming extinct are found also flying and walking dinosaurs, which include all land animals that had masses greater than 25 kg. The present investigation is concerned with a study of the possibilities for the collision of earth with 10 km-size object, and the consequences produced by such a collision. It is found that the penetration of the atmosphere by the bolide creates a temporary hole in the atmosphere. The resulting flow fields can inject melt droplets and finely commuted solid particles into the atmosphere. Short-term effects of heating, followed by dust induced worldwide cooling, may provide several mechanisms for the observed extinction of the species.

  5. Macroecological analyses support an overkill scenario for late Pleistocene extinctions.

    PubMed

    Diniz-Filho, J A F

    2004-08-01

    The extinction of megafauna at the end of Pleistocene has been traditionally explained by environmental changes or overexploitation by human hunting (overkill). Despite difficulties in choosing between these alternative (and not mutually exclusive) scenarios, the plausibility of the overkill hypothesis can be established by ecological models of predator-prey interactions. In this paper, I have developed a macroecological model for the overkill hypothesis, in which prey population dynamic parameters, including abundance, geographic extent, and food supply for hunters, were derived from empirical allometric relationships with body mass. The last output correctly predicts the final destiny (survival or extinction) for 73% of the species considered, a value only slightly smaller than those obtained by more complex models based on detailed archaeological and ecological data for each species. This illustrates the high selectivity of Pleistocene extinction in relation to body mass and confers more plausibility on the overkill scenario.

  6. Sexual selection affects local extinction and turnover in bird communities

    USGS Publications Warehouse

    Doherty, P.F.; Sorci, G.; Royle, J. Andrew; Hines, J.E.; Nichols, J.D.; Boulinier, T.

    2003-01-01

    Predicting extinction risks has become a central goal for conservation and evolutionary biologists interested in population and community dynamics. Several factors have been put forward to explain risks of extinction, including ecological and life history characteristics of individuals. For instance, factors that affect the balance between natality and mortality can have profound effects on population persistence. Sexual selection has been identified as one such factor. Populations under strong sexual selection experience a number of costs ranging from increased predation and parasitism to enhanced sensitivity to environmental and demographic stochasticity. These findings have led to the prediction that local extinction rates should be higher for species/populations with intense sexual selection. We tested this prediction by analyzing the dynamics of natural bird communities at a continental scale over a period of 21 years (1975-1996), using relevant statistical tools. In agreement with the theoretical prediction, we found that sexual selection increased risks of local extinction (dichromatic birds had on average a 23% higher local extinction rate than monochromatic species). However, despite higher local extinction probabilities, the number of dichromatic species did not decrease over the period considered in this study. This pattern was caused by higher local turnover rates of dichromatic species, resulting in relatively stable communities for both groups of species. Our results suggest that these communities function as metacommunities, with frequent local extinctions followed by colonization. Anthropogenic factors impeding dispersal might therefore have a significant impact on the global persistence of sexually selected species.

  7. Environmental effects of large impacts on the earth; relation to extinction mechanisms

    NASA Technical Reports Server (NTRS)

    Okeefe, John D.; Ahrens, Thomas J.; Koschny, Detlef

    1988-01-01

    Since Alvarez et al., discovered a worldwide approx. cm-thick layer of fine sediments laden with platinum group elements in approximately chondritic proportions exactly at the Cretaceous-Tertiary (C-T) boundary, and proposed bolide-impact as triggering mass extinctions, many have studied this hypothesis and the layer itself with its associated spherules and shocked quartz. At issue is whether the mass extinctions, and this horizon has an impact versus volcanic origin. A critical feature of the Alvarez hypothesis is the suggestion that the bolide or possibly a shower of objects delivered to the earth approx. 0.6 x 10 to the 18th power g of material which resulted in aerosol-sized ejecta such that global insolation was drastically reduced for significant periods. Such an event would lower temperatures on continents and halt photosynthesis in the upper 200 m of th eocean. The latter would strangle the marine food chain and thus produce the major marine faunal extinctions which mark the C-T boundary. Crucial issues examined include: What are the dynamics of atmospheric flow occurring upon impact of a large bolide with the earth; What is the size distributions of the very fine impact ejecta and how do these compare to the models of ejecta which are used to model the earth's radiative thermal balance. The flow field due to passage of a 10 km diameter bolide through an exponential atmosphere and the interaction of the gas flow and bolide with the solid ear was calculated. The CO2 released upon impact onto shallow marine carbonate sections was modeled and found that the mass of CO2 released exceeds the present 10 to the 18th power g CO2 budget of the earth's atmosphere by several times. Using the calculations of Kasting and Toon it was found that to compute the temperature rise of the earth's surface as a function of CO2 content, it was found that sudden and prolonged global increases are induced from impact of 20 to 50 km radius projectiles and propose that sudden

  8. The fossil record of evolution: Data on diversification and extinction

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. John, Jr.

    1990-01-01

    The two principle efforts include: (1) a compilation of a synoptic, mesoscale data base on times of origination and extinction of animal genera in the oceans over the last 600 million years of geologic time; and (2) an analysis of statistical patterns in these data that relate to the diversification of complex life and to the occurrence of mass extinctions, especially those that might be associated with extraterrestrial phenomena. The data base is unique in its taxonomic scope and detail and in its temporal resolution. It is a valuable resource for investigating evolutionary expansions and extinctions of complex life.

  9. Spectroscopic Infrared Extinction Mapping as a Probe of Grain Growth in IRDCs

    NASA Astrophysics Data System (ADS)

    Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

    2015-11-01

    We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim & Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3-8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14-38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffuse Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR-FIR opacity laws that lack the ˜12 and ˜35 μm features associated with the thick water ice mantle models of Ossenkopf & Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

  10. Infrared Extinction and Stellar Populations in the Milky Way Midplane

    NASA Astrophysics Data System (ADS)

    Zasowski, Gail; Majewski, S. R.; Benjamin, R. A.; Nidever, D. L.; Skrutskie, M. F.; Indebetouw, R.; Patterson, R. J.; Meade, M. R.; Whitney, B. A.; Babler, B.; Churchwell, E.; Watson, C.

    2012-01-01

    The primary laboratory for developing and testing models of galaxy formation, structure, and evolution is our own Milky Way, the closest large galaxy and the only one in which we can resolve large numbers of individual stars. The recent availability of extensive stellar surveys, particularly infrared ones, has enabled precise, contiguous measurement of large-scale Galactic properties, a major improvement over inferences based on selected, but scattered, sightlines. However, our ability to fully exploit the Milky Way as a galactic laboratory is severely hampered by the fact that its midplane and central bulge -- where most of the Galactic stellar mass lies -- is heavily obscured by interstellar dust. Therefore, proper consideration of the interstellar extinction is crucial. This thesis describes a new extinction-correction method (the RJCE method) that measures the foreground extinction towards each star and, in many cases, enables recovery of its intrinsic stellar type. We have demonstrated the RJCE Method's validity and used it to produce new, reliable extinction maps of the heavily-reddened Galactic midplane. Taking advantage of the recovered stellar type information, we have generated maps probing the extinction at different heliocentric distances, thus yielding information on the elusive three-dimensional distribution of the interstellar dust. We also performed a study of the interstellar extinction law itself which revealed variations previously undetected in the diffuse ISM and established constraints on models of ISM grain formation and evolution. Furthermore, we undertook a study of large-scale stellar structure in the inner Galaxy -- the bar(s), bulge(s), and inner spiral arms. We used observed and extinction-corrected infrared photometry to map the coherent stellar features in these heavily-obscured parts of the Galaxy, placing constraints on models of the central stellar mass distribution.

  11. Possible climate effects of the CAMP intrusive and extrusive activity and its influence on the end-Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Marzoli, A.; Davies, J.; Valeriani, L.; Preto, N.; Cirilli, S.; Panfili, G.; Dal Corso, J.; Vasconcellos, E.; Ernesto, M.; Youbi, N.; Callegaro, S.

    2017-12-01

    The end-Triassic global climate changes were probably triggered by the emplacement of the CAMP (Central Atlantic magmatic province). Here we explore the possibility that CAMP intrusions triggered global warming, while CAMP eruptions triggered short-lived cooling events. The main phase of the end-Triassic environmental changes and mass extinction was marked by two carbon isotopic excursions (CIEs). Based on stratigraphic and geochronologic data, we show that the earliest CAMP intrusions were emplaced at ca. 201.6 Ma prior to the first CIE (Davies et al., 2017). The main phase of CAMP magmatism started during the first CIE at ca. 201.5 Ma and continued until the second CIE and the Triassic-Jurassic boundary (at ca. 201.3 Ma). In particular, intrusion of the over 1 million cubic km of basaltic sills in Amazonia (Brazil) and of widespread sills from North America and Africa occurred within this interval. Multidisciplinary analyses show that organic matter rich sediments close to the sills from Brazil, Morocco, and the USA underwent contact metamorphism and organic carbon depletion. Such process may have released large amounts of thermogenic gases (CO2 and CH4) leading to global perturbation of the carbon cycle and to global warming. The timing of CAMP volcanic eruptions is well constrained by combined geochronologic, stratigraphic and palynologic data. In Morocco, newly observed palynological assemblages for sediments at the top of the lava piles are nearly identical to those found at the base of the volcanic sequences. These new data combined with carbon isotopic data indicate that over 95% of the CAMP lava flows in Morocco erupted during a short time interval at the very beginning of the end-Triassic extinction interval. A similar scenario applies possibly to the lava flows from North America. CAMP basalts are quite sulfur rich (up to 1800 ppm) suggesting that CAMP eruptions emitted large amounts of SO2. Such emissions lead possibly to short-lived cooling events

  12. THE MID-INFRARED EXTINCTION LAW AND ITS VARIATION IN THE COALSACK NEBULA

    SciTech Connect

    Wang Shu; Gao Jian; Jiang, B. W.

    In recent years, the wavelength dependence of interstellar extinction from the ultraviolet (UV) to the near- and mid-infrared (IR) has been studied extensively. Although it is well established that the UV/optical extinction law varies significantly among the different lines of sight, it is not clear how IR extinction varies among various environments. In this work, using the color-excess method and taking red giants as the extinction tracer, we determine interstellar extinction A{sub {lambda}} in the four Spitzer/IRAC bands in [3.6], [4.5], [5.8], [8.0] {mu}m (relative to A{sub K{sub s}}, extinction in the Two Micron All Sky Survey (2MASS) K{sub s}more » band at 2.16 {mu}m) of the Coalsack nebula, a nearby starless dark cloud, based on the data obtained from the 2MASS and Spitzer/GLIMPSE surveys. We select five individual regions across the nebula that span a wide variety of physical conditions ranging from diffuse and translucent to dense environments, as traced by the visual extinction, the Spitzer/MIPS 24 {mu}m emission, and CO emission. We find that A{sub {lambda}}/A{sub K{sub s}}, mid-IR extinction relative to A{sub K{sub s}}, decreases from diffuse to dense environments, which may be explained in terms of ineffective dust growth in dense regions. The mean extinction (relative to A{sub K{sub s}}) is calculated for the four IRAC bands as well and exhibits a flat mid-IR extinction law consistent with previous determinations for other regions. Extinction in the IRAC 4.5 {mu}m band is anomalously high, much higher than that of the other three IRAC bands, and cannot be explained in terms of CO and CO{sub 2} ice. Mid-IR extinction in the four IRAC bands has also been derived for four representative regions in the Coalsack Globule 2, which respectively exhibit strong ice absorption, moderate or weak ice absorption, and very weak or no ice absorption. The derived mid-IR extinction curves are all flat, with A{sub {lambda}}/A{sub K{sub s}} increasing with the decrease

  13. Temporal Dynamics of Recovery from Extinction Shortly after Extinction Acquisition

    ERIC Educational Resources Information Center

    Archbold, Georgina E.; Dobbek, Nick; Nader, Karim

    2013-01-01

    Evidence suggests that extinction is new learning. Memory acquisition involves both short-term memory (STM) and long-term memory (LTM) components; however, few studies have examined early phases of extinction retention. Retention of auditory fear extinction was examined at various time points. Shortly (1-4 h) after extinction acquisition…

  14. Interstellar extinction from photometric surveys: application to four high-latitude areas

    NASA Astrophysics Data System (ADS)

    Malkov, Oleg; Karpov, Sergey; Kilpio, Elena; Sichevsky, Sergey; Chulkov, Dmitry; Dluzhnevskaya, Olga; Kovaleva, Dana; Kniazev, Alexei; Mickaelian, Areg; Mironov, Alexey; Murthy, Jayant; Sytov, Alexey; Zhao, Gang; Zhukov, Aleksandr

    2018-04-01

    Information on interstellar extinction and dust properties may be obtained from modern large photometric surveys data. Virtual Observatory facilities allow users to make a fast and correct cross-identification of objects from various surveys. It yields a multicolor photometry data on detected objects and makes it possible to estimate stellar parameters and calculate interstellar extinction. A 3D extinction map then can be constructed. The method was applied to 2MASS, SDSS, GALEX and UKIDSS surveys. Results for several high-latitude areas are obtained, compared with independent sources and discussed here.

  15. Spectroscopic infrared extinction mapping as a probe of grain growth in IRDCs

    NASA Astrophysics Data System (ADS)

    Lim, Wanggi; Carey, Sean J.

    2014-07-01

    We present photometric and spectroscopic tests of MIR to FIR extinction laws toward IRDC G028.36+00.07, a potential site of massive star formation. Lim & Tan (2014, hereafter LT14) developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 micron and Herschel-PACS 70 micron images, and extending the MIR 8 micron mapping methods of (Butler & Tan 2012, hereafter BT12), finding evidence for grain growth in the highest mass surface density regions. Here we present initial results of spectroscopic infrared extinction (SIREX) mapping using Spitzer-IRS (14 to 38 micron) data of the same IRDC. These methods allow us to measure the SED of the diffuse Galactic ISM, which we compare to theoretical models of Draine & Li (2007), as well as to search for opacity law variations with mass surface density within the IRDC. By comparison with theoretical dust models, e.g., Ossenkopf & Henning (1994) and Ormel et al. (2011), we are able to search for compositional signatures of the grain ices, such as water and methanol. We find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

  16. Proposed law of nature linking impacts, plume volcanism, and Milankovitch cycles to terrestrial vertebrate mass extinctions via greenhouse-embryo death coupling

    NASA Technical Reports Server (NTRS)

    Mclean, D. M.

    1994-01-01

    A greenhouse-physiological coupling killing mechanism active among mammals, birds, and reptiles has been identified. Operating via environmental thermal effects upon the maternal core-skin blood flow critical to the survival and development of embryos, it reduces the flow of blood to the uterine tract. Today, during hot summers, this phenomena kills embryos on a vast, global scale. Because of sensitivity of many mammals to modern heat, a major modern greenhouse could reduce population numbers on a global scale, and potentially trigger population collapses in the more vulnerable parts of the world. In the geological past, the killing mechanism has likely been triggered into action by greenhouse warming via impact events, plume volcanism, and Earth orbital variations (Milankovitch cycles). Earth's biosphere is maintained and molded by the flow of energy from the solar energy source to Earth and on to the space energy sink (SES). This SES energy flow maintains Earth's biosphere and its living components, as open, intermediate, dissipative, nonequilibrium systems whose states are dependent upon the rate of energy flowing through them. Greenhouse gases such as CO2 in the atmosphere influence the SES energy flow rate. Steady-state flow is necessary for global ecological stability (autopoiesis). Natural fluctuations of the C cycle such as rapid releases of CO2 from the mantle, or oceans, disrupt steady-state SES flow. These fluctuations constantly challenge the biosphere; slowdown of SES energy flow drives it toward thermodynamical equilibrium and stagnation. Fluctuations induced by impact event, mantle plume volcanism, and Milankovitch cycles can grow into structure-breaking waves triggering major perturbations of Earth's C cycle and mass extinctions. A major C cycle perturbation involves readjustment of the outer physiochemical spheres of the Earth: the atmosphere, hydrosphere, and lithosphere; and by necessity, the biosphere. A greenhouse, one manifestation of a major

  17. Progress towards a universal family of UV-IR extinction laws

    NASA Astrophysics Data System (ADS)

    Maíz Apellániz, J.; Trigueros Páez, E.; Bostroem, A. K.; Barbá, R. H.; Evans, C. J.

    2017-03-01

    We present our progress on the study of extinction laws along three diferent lines. [a] We compare how well different families of extinction laws fit existing photometric data for Galactic sightlines and we find that the Maíz Apellániz et al. (2014) family provides better results than those of Cardelli et al. (1989) or Fitzpatrick (1999). [b] We describe the HST/STIS spectrophotometry in the 1700-10 200 Å range that we are obtaining for several tens of sightlines in 30 Doradus with the purpose of deriving an improved wavelength-detailed family of extinction laws. [c] We present the study we are conducting on the behavior of the extinction law in the infrared by combining 2MASS and WISE photometry with Spitzer and ISO spectrophotometry.

  18. Brain structural connectivity and context-dependent extinction memory.

    PubMed

    Hermann, Andrea; Stark, Rudolf; Blecker, Carlo R; Milad, Mohammed R; Merz, Christian J

    2017-08-01

    Extinction of conditioned fear represents an important mechanism in the treatment of anxiety disorders. Return of fear after successful extinction or exposure therapy in patients with anxiety disorders might be linked to poor temporal or contextual generalization of extinction due to individual differences in brain structural connectivity. The goal of this magnetic resonance imaging study was therefore to investigate the association of context-dependent extinction recall with brain structural connectivity. Diffusion-tensor imaging was used to determine the fractional anisotropy as a measure of white matter structural integrity of fiber tracts connecting central brain regions of the fear and extinction circuit (uncinate fasciculus, cingulum). Forty-five healthy men participated in a two-day fear conditioning experiment with fear acquisition in context A and extinction learning in context B on the first day. Extinction recall in the extinction context as well as renewal in the acquisition context and a novel context C took place one day later. Renewal of conditioned fear (skin conductance responses) in the acquisition context was associated with higher structural integrity of the hippocampal part of the cingulum. Enhanced structural integrity of the cingulum might be related to stronger hippocampal modulation of the dorsal anterior cingulate cortex, a region important for modulating conditioned fear output by excitatory projections to the amygdala. This finding underpins the crucial role of individual differences in the structural integrity of relevant fiber tracts for context-dependent extinction recall and return of fear after exposure therapy in anxiety disorders. © 2017 Wiley Periodicals, Inc.

  19. Role of degassing of the Noril’sk nickel deposits in the Permian–Triassic mass extinction event

    PubMed Central

    Barnes, Stephen J.; Mungall, James E.

    2017-01-01

    The largest mass extinction event in Earth's history marks the boundary between the Permian and Triassic Periods at circa 252 Ma and has been linked with the eruption of the basaltic Siberian Traps large igneous province (SLIP). One of the kill mechanisms that has been suggested is a biogenic methane burst triggered by the release of vast amounts of nickel into the atmosphere. A proposed Ni source lies within the huge Noril’sk nickel ore deposits, which formed in magmatic conduits widely believed to have fed the eruption of the SLIP basalts. However, nickel is a nonvolatile element, assumed to be largely sequestered at depth in dense sulfide liquids that formed the orebodies, preventing its release into the atmosphere and oceans. Flotation of sulfide liquid droplets by surface attachment to gas bubbles has been suggested as a mechanism to overcome this problem and allow introduction of Ni into the atmosphere during eruption of the SLIP lavas. Here we use 2D and 3D X-ray imagery on Noril’sk nickel sulfide, combined with simple thermodynamic models, to show that the Noril’sk ores were degassing while they were forming. Consequent “bubble riding” by sulfide droplets, followed by degassing of the shallow, sulfide-saturated, and exceptionally volatile and Cl-rich SLIP lavas, permitted a massive release of nickel-rich volcanic gas and subsequent global dispersal of nickel released from this gas as aerosol particles. PMID:28223492

  20. Unusual dynamics of extinction in a simple ecological model.

    PubMed Central

    Sinha, S; Parthasarathy, S

    1996-01-01

    Studies on natural populations and harvesting biological resources have led to the view, commonly held, that (i) populations exhibiting chaotic oscillations run a high risk of extinction; and (ii) a decrease in emigration/exploitation may reduce the risk of extinction. Here we describe a simple ecological model with emigration/depletion that shows behavior in contrast to this. This model displays unusual dynamics of extinction and survival, where populations growing beyond a critical rate can persist within a band of high depletion rates, whereas extinction occurs for lower depletion rates. Though prior to extinction at lower depletion rates the population exhibits chaotic dynamics with large amplitudes of variation and very low minima, at higher depletion rates the population persists at chaos but with reduced variation and increased minima. For still higher values, within the band of persistence, the dynamics show period reversal leading to stability. These results illustrate that chaos does not necessarily lead to population extinction. In addition, the persistence of populations at high depletion rates has important implications in the considerations of strategies for the management of biological resources. PMID:8643661

  1. Rethinking Extinction

    PubMed Central

    Dunsmoor, Joseph E.; Niv, Yael; Daw, Nathaniel; Phelps, Elizabeth A.

    2015-01-01

    Extinction serves as the leading theoretical framework and experimental model to describe how learned behaviors diminish through absence of anticipated reinforcement. In the past decade, extinction has moved beyond the realm of associative learning theory and behavioral experimentation in animals and has become a topic of considerable interest in the neuroscience of learning, memory, and emotion. Here, we review research and theories of extinction, both as a learning process and as a behavioral technique, and consider whether traditional understandings warrant a re-examination. We discuss the neurobiology, cognitive factors, and major computational theories, and revisit the predominant view that extinction results in new learning that interferes with expression of the original memory. Additionally, we reconsider the limitations of extinction as a technique to prevent the relapse of maladaptive behavior, and discuss novel approaches, informed by contemporary theoretical advances, that augment traditional extinction methods to target and potentially alter maladaptive memories. PMID:26447572

  2. On the accuracy of stratospheric aerosol extinction derived from in situ size distribution measurements and surface area density derived from remote SAGE II and HALOE extinction measurements

    DOE PAGES

    Kovilakam, Mahesh; Deshler, Terry

    2015-08-26

    In situ stratospheric aerosol measurements, from University of Wyoming optical particle counters (OPCs), are compared with Stratospheric Aerosol Gas Experiment (SAGE) II (versions 6.2 and 7.0) and Halogen Occultation Experiment (HALOE) satellite measurements to investigate differences between SAGE II/HALOE-measured extinction and derived surface area and OPC-derived extinction and surface area. Coincident OPC and SAGE II measurements are compared for a volcanic (1991-1996) and nonvolcanic (1997-2005) period. OPC calculated extinctions agree with SAGE II measurements, within instrumental uncertainty, during the volcanic period, but have been a factor of 2 low during the nonvolcanic period. Three systematic errors associated with the OPCmore » measurements, anisokineticity, inlet particle evaporation, and counting efficiency, were investigated. An overestimation of the OPC counting efficiency is found to be the major source of systematic error. With this correction OPC calculated extinction increases by 15-30% (30-50%) for the volcanic (nonvolcanic) measurements. These changes significantly improve the comparison with SAGE II and HALOE extinctions in the nonvolcanic cases but slightly degrade the agreement in the volcanic period. These corrections have impacts on OPC-derived surface area density, exacerbating the poor agreement between OPC and SAGE II (version 6.2) surface areas. Furthermore, this disparity is reconciled with SAGE II version 7.0 surface areas. For both the volcanic and nonvolcanic cases these changes in OPC counting efficiency and in the operational SAGE II surface area algorithm leave the derived surface areas from both platforms in significantly better agreement and within the ± 40% precision of the OPC moment calculations.« less

  3. On the accuracy of stratospheric aerosol extinction derived from in situ size distribution measurements and surface area density derived from remote SAGE II and HALOE extinction measurements

    SciTech Connect

    Kovilakam, Mahesh; Deshler, Terry

    In situ stratospheric aerosol measurements, from University of Wyoming optical particle counters (OPCs), are compared with Stratospheric Aerosol Gas Experiment (SAGE) II (versions 6.2 and 7.0) and Halogen Occultation Experiment (HALOE) satellite measurements to investigate differences between SAGE II/HALOE-measured extinction and derived surface area and OPC-derived extinction and surface area. Coincident OPC and SAGE II measurements are compared for a volcanic (1991-1996) and nonvolcanic (1997-2005) period. OPC calculated extinctions agree with SAGE II measurements, within instrumental uncertainty, during the volcanic period, but have been a factor of 2 low during the nonvolcanic period. Three systematic errors associated with the OPCmore » measurements, anisokineticity, inlet particle evaporation, and counting efficiency, were investigated. An overestimation of the OPC counting efficiency is found to be the major source of systematic error. With this correction OPC calculated extinction increases by 15-30% (30-50%) for the volcanic (nonvolcanic) measurements. These changes significantly improve the comparison with SAGE II and HALOE extinctions in the nonvolcanic cases but slightly degrade the agreement in the volcanic period. These corrections have impacts on OPC-derived surface area density, exacerbating the poor agreement between OPC and SAGE II (version 6.2) surface areas. Furthermore, this disparity is reconciled with SAGE II version 7.0 surface areas. For both the volcanic and nonvolcanic cases these changes in OPC counting efficiency and in the operational SAGE II surface area algorithm leave the derived surface areas from both platforms in significantly better agreement and within the ± 40% precision of the OPC moment calculations.« less

  4. Evolution and mass extinctions as lognormal stochastic processes

    NASA Astrophysics Data System (ADS)

    Maccone, Claudio

    2014-10-01

    -terrestrial civilizations existing in the Galaxy (as a consequence of the central limit theorem of statistics). (5) But the most striking new result is that the well-known `Molecular Clock of Evolution', namely the `constant rate of Evolution at the molecular level' as shown by Kimura's Neutral Theory of Molecular Evolution, identifies with growth rate of the entropy of our Evo-SETI model, because they both grew linearly in time since the origin of life. (6) Furthermore, we apply our Evo-SETI model to lognormal stochastic processes other than GBMs. For instance, we provide two models for the mass extinctions that occurred in the past: (a) one based on GBMs and (b) the other based on a parabolic mean value capable of covering both the extinction and the subsequent recovery of life forms. (7) Finally, we show that the Markov & Korotayev (2007, 2008) model for Darwinian Evolution identifies with an Evo-SETI model for which the mean value of the underlying lognormal stochastic process is a cubic function of the time. In conclusion: we have provided a new mathematical model capable of embracing molecular evolution, SETI and entropy into a simple set of statistical equations based upon b-lognormals and lognormal stochastic processes with arbitrary mean, of which the GBMs are the particular case of exponential growth.

  5. Geography of cretaceous extinctions: Data base development

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1991-01-01

    Data bases built from the source literature are plagued by problems of data quality. Unless the data acquisition is done by experts, working slowly, the data base may contain so much garbage that true signals and patterns cannot be detected. On the other hand, high quality data bases develop so slowly that satisfactory statistical analysis may never be possible due to the small sample sizes. Results of a test are presented of the opposite strategy: rapid data acquisition by non-experts with minimal control on data quality. A published list of 186 species and genera of fossil invertibrates of the latest Cretaceous Age (Maestrichtian) were located through a random search of the paleobiological and geological literature. The geographic location for each faunal list was then transformed electronically to Maestrichtian latitude and longitude and the lists were further digested to identify the genera occurring in each ten-degree, latitude-longitude block. The geographical lists were clustered using the Otsuka similarity coefficient and a standard unweight-pair-group method. The resulting clusters are remarkably consistent geographically, indicating that a strong biogeographic signal is visible despite low-quality data. A further test evaluated the geographic pattern of end-Cretaceaous extinctions. All genera in the data base were compared with Sepkoski's compendium of time ranges of genera to determine which of the reported genera survived the Cretaceous mass extinction. In turn, extinction rates for the ten-degree, latitude-longitude blocks were mapped. The resulting distribution is readily interpretable as a robust pattern of the geography of the mass extinction. The study demonstrates that a low-quality data base, built rapidly, can provide a basis for meaningful analysis of past biotic events.

  6. SPECTROSCOPIC INFRARED EXTINCTION MAPPING AS A PROBE OF GRAIN GROWTH IN IRDCs

    SciTech Connect

    Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

    We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim and Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3–8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14–38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffusemore » Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR–FIR opacity laws that lack the ∼12 and ∼35 μm features associated with the thick water ice mantle models of Ossenkopf and Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.« less

  7. Dynamics of Long-period Comets

    NASA Technical Reports Server (NTRS)

    Weissman, P. R.

    1985-01-01

    Dynamical studies of the origin and evolution of long period comets in the Oort cloud during the past year have concentrated on four areas: (1) interpretation of IRAS observations of dust shells around Vega and some 40 other main sequence stars as evidence for cometary clouds around each of these stars; (2) the dynamical plausibility of an unseen solar companion star orbiting in the Oort cloud and causing periodic cometary showers which result in biological extinction events on the earth; (3) a review of the current hypotheses for cometary formation with particular attention to how each mechanism supplies the required mass of comets to the Oort cloud; and (4) development of new dynamics software to simulate the passage of individual stars directly through the Oort cloud. Each of these efforts is described in detail.

  8. Fear Extinction as a Model for Translational Neuroscience: Ten Years of Progress

    PubMed Central

    Milad, Mohammed R.; Quirk, Gregory J.

    2016-01-01

    The psychology of extinction has been studied for decades. Approximately 10 years ago, however, there began a concerted effort to understand the neural circuits of extinction of fear conditioning, in both animals and humans. Progress during this period has been facilitated by an unusual degree of coordination between rodent and human researchers examining fear extinction. This successful research program could serve as a model for translational research in other areas of behavioral neuroscience. Here we review the major advances and highlight new approaches to understanding and exploiting fear extinction. PMID:22129456

  9. Dinasour extinction and volcanic activity

    NASA Astrophysics Data System (ADS)

    Gledhill, J. A.

    There is at present some controversy about the reason for the mass extinction of dinosaurs and other forms of life at the end of the Cretaceous. A suggestion by Alvarez et al. [1980] that this was due to the collision of the earth with a meteorite 10 km or so in diameter has excited considerable interest [Silver and Schultz, 1982] and also some criticism [Stanley, 1984]. A recent publication [Wood, 1984] describing the catastrophic effects of a relatively minor lava flow in Iceland suggests that intense volcanic activity could have played a large part in the extinctions. In this letter it is pointed out that the Deccan lava flows in India took place in the appropriate time and may well have been of sufficient magnitude to be a major factor in the Cretaceous-Tertiary (C-T) boundary catastrophe.

  10. Context-dependent extinction of an appetitive operant conditioned response in infant rats.

    PubMed

    Orellana Barrera, Estefanía; Arias, Carlos; González, Felisa; Abate, Paula

    2017-04-01

    The present study evaluated context-dependent learning under an operant conditioning procedure in infant rats. Preweanling rats were trained in context A during postnatal days (PDs) 16 and 17 to learn an appetitive operant conditioning task, employing milk chocolate as appetitive reinforcer. On PD18 the operant response was extinguished in context A, or in an alternative context B. The change from context A to B between acquisition and extinction did not affect the number of responses during extinction, but slightly modified the shape of the extinction curve. On PD19, a renewal test conducted in context A clearly showed ABA-renewal of the extinguished operant response. These results add to the body of evidence indicating that infants are able to acquire and retain contextual information, and support the notion that extinction during this ontogenetic period involves new learning. © 2017 Wiley Periodicals, Inc.

  11. Abrupt Climatic Change during the Latest Maastrichtian: Establishing Robust Temporal Links with the Onset of Deccan Volcanism and K/Pg Mass Extinction

    NASA Astrophysics Data System (ADS)

    Barnet, J.; Littler, K.; Kroon, D.; Leng, M. J.; Westerhold, T.; Roehl, U.; Zachos, J. C.

    2017-12-01

    A transient period of climate change, characterized by a global warming of 2.5-5°C followed by a cooling to pre-excursion conditions, occurred during the last 300 kyr of the Maastrichtian ( 66.34-66.02 Ma). This instability may have played a role in destabilizing marine and terrestrial ecosystems, priming the system for abrupt extinction at the K-Pg boundary, likely triggered by a large bolide impact. This pre-K-Pg warming event has often been linked to the main phase of Deccan Trap volcanism, however large uncertainties associated with radio-isotopic dating methods of basalts, along with low sedimentation rates and hiatuses in many studied sedimentary sequences, have long hampered a definitive correlation. To complement recent advances in dating of the traps, we have generated the first complete and highest resolution (2.5-4 kyr) benthic stable δ13C and δ18O record for the final million years of the Maastrichtian using the epifaunal foraminifera species Nuttallides truempyi from ODP Site 1262, Walvis Ridge, South Atlantic, calibrated to an updated orbitally-tuned age model. We then compare our data to other previously published geochemical data from other sites in the high, middle, and low latitudes. Our data confirms that the onset of the warming event coincides with the onset of the main phase of Deccan volcanism, strongly suggesting a causal link. Furthermore, spectral analysis of our extended late Maastrichtian-Early Eocene record suggests that the onset of the warming event corresponds to a 405-kyr eccentricity minima, in contrast to many transient warming events (hyperthermals) of the Paleogene, suggesting a control by orbital forcing alone is unlikely. A peculiar feature of the event, compared to other hyperthermals, is a muted carbon cycle response during warming, which may be related to the comparatively heavier δ13C signature of volcanogenic CO2 (-7‰), compared to other sources of light carbon invoked to explain Paleogene hyperthermals. The warming

  12. Seed dispersal anachronisms: rethinking the fruits extinct megafauna ate.

    PubMed

    Guimarães, Paulo R; Galetti, Mauro; Jordano, Pedro

    2008-03-05

    Some neotropical, fleshy-fruited plants have fruits structurally similar to paleotropical fruits dispersed by megafauna (mammals > 10(3) kg), yet these dispersers were extinct in South America 10-15 Kyr BP. Anachronic dispersal systems are best explained by interactions with extinct animals and show impaired dispersal resulting in altered seed dispersal dynamics. We introduce an operational definition of megafaunal fruits and perform a comparative analysis of 103 Neotropical fruit species fitting this dispersal mode. We define two megafaunal fruit types based on previous analyses of elephant fruits: fruits 4-10 cm in diameter with up to five large seeds, and fruits > 10 cm diameter with numerous small seeds. Megafaunal fruits are well represented in unrelated families such as Sapotaceae, Fabaceae, Solanaceae, Apocynaceae, Malvaceae, Caryocaraceae, and Arecaceae and combine an overbuilt design (large fruit mass and size) with either a single or few (< 3 seeds) extremely large seeds or many small seeds (usually > 100 seeds). Within-family and within-genus contrasts between megafaunal and non-megafaunal groups of species indicate a marked difference in fruit diameter and fruit mass but less so for individual seed mass, with a significant trend for megafaunal fruits to have larger seeds and seediness. Megafaunal fruits allow plants to circumvent the trade-off between seed size and dispersal by relying on frugivores able to disperse enormous seed loads over long-distances. Present-day seed dispersal by scatter-hoarding rodents, introduced livestock, runoff, flooding, gravity, and human-mediated dispersal allowed survival of megafauna-dependent fruit species after extinction of the major seed dispersers. Megafauna extinction had several potential consequences, such as a scale shift reducing the seed dispersal distances, increasingly clumped spatial patterns, reduced geographic ranges and limited genetic variation and increased among-population structuring. These effects

  13. Optimum periodicity of repeated contractile actions applied in mass transport

    NASA Astrophysics Data System (ADS)

    Ahn, Sungsook; Lee, Sang Joon

    2015-01-01

    Dynamically repeated periodic patterns are abundant in natural and artificial systems, such as tides, heart beats, stock prices, and the like. The characteristic repeatability and periodicity are expected to be optimized in effective system-specific functions. In this study, such optimum periodicity is experimentally evaluated in terms of effective mass transport using one-valve and multi-valve systems working in contractile fluid flows. A set of nanoscale gating functions is utilized, operating in nanocomposite networks through which permeates selectively pass under characteristic contractile actions. Optimized contractile periodicity exists for effective energy impartment to flow in a one-valve system. In the sequential contractile actions for a multi-valve system, synchronization with the fluid flow is critical for effective mass transport. This study provides fundamental understanding on the various repeated periodic patterns and dynamic repeatability occurring in nature and mechanical systems, which are useful for broad applications.

  14. Dynamics of Droplet Extinction in Slow Convective Flows

    NASA Technical Reports Server (NTRS)

    Nayagam, V.; Haggard, J. B., Jr.; Williams, F. A.

    1999-01-01

    The classical model for droplet combustion predicts that the square of the droplet diameter decreases linearly with time. It also predicts that a droplet of any size will burn to completion over a period of time. However, it has been known for some time that under certain conditions flames surrounding a droplet, in a quiescent environment, could extinguish because of insufficient residence time for the chemistry to proceed to completion. This type of extinction that occurs for smaller droplets has been studied extensively in the past. Large droplets, on the other hand, exhibit a different type of extinction where excessive radiative heat loss from the flame zone leads to extinction. This mode of "radiative extinction" was theoretically predicted for droplet burning by Chao et al. and was observed in recent space experiments in a quiescent environment. Thus far, the fundamental flammability limit prescribed by radiative extinction of liquid droplets has been measured only under quiescent environmental conditions. In many space platforms, however, ventilation systems produce small convective flows and understanding of the influences of this convection on the extinction process will help better define the radiative extinction flammability boundaries. Boundaries defined by experiments and captured using theoretical models could provide enhanced fire safety margin in space explor1999063d investigation of convective effects will help in interpretations of burning-rate data obtained during free-floated droplet combustion experiments with small residual velocities.

  15. d-Cycloserine facilitates extinction learning and enhances extinction-related brain activation.

    PubMed

    Klass, Anne; Glaubitz, Benjamin; Tegenthoff, Martin; Lissek, Silke

    2017-10-01

    Extinction learning is modulated by N-methyl d-aspartate receptors (NMDAR) particularly in prefrontal and hippocampal brain regions. The use of of NMDA agonists in exposure therapy of anxiety disorders has been investigated in various patient groups. Behavioral results showed beneficial effects of pre-learning administration of the partial NMDAR agonist d-Cycloserine (DCS) on therapy success. However, the impact of DCS upon non-fear-related contextual extinction, and associated recruitment of extinction-relevant brain regions is as yet unknown. In the present fMRI study, healthy human participants performed a context-related associative learning and extinction task. A single dose of DCS, administered prior to extinction learning, enhanced extinction learning performance in an identical context, and increased activation in prefrontal, temporal as well as hippocampal/insular regions, compared to placebo controls. In contrast, DCS did not affect extinction learning in a novel context, nor the renewal effect, which describes the recovery of an extinguished response if the context of extinction differs from the context of recall. Our findings demonstrate a specific involvement of prefrontal and hippocampal NMDAR in the modification of established stimulus-outcome associations in identical contexts and thus their role in behavioral flexibility, underlining their potential for enhancing AAA extinction learning. Copyright © 2017. Published by Elsevier Inc.

  16. Is extinction forever?

    PubMed Central

    Bridge, Eli S.; Crawford, Priscilla H. C.; Hough, Daniel J.; Kelly, Jeffrey F.; Patten, Michael A.

    2015-01-01

    Mistrust of science has seeped into public perception of the most fundamental aspect of conservation—extinction. The term ought to be straightforward, and yet, there is a disconnect between scientific discussion and public views. This is not a mere semantic issue, rather one of communication. Within a population dynamics context, we say that a species went locally extinct, later to document its return. Conveying our findings matters, for when we use local extinction, an essentially nonsensical phrase, rather than extirpation, which is what is meant, then we contribute to, if not create outright, a problem for public understanding of conservation, particularly as local extinction is often shortened to extinction in media sources. The public that receives the message of our research void of context and modifiers comes away with the idea that extinction is not forever or, worse for conservation as a whole, that an extinction crisis has been invented. PMID:25711479

  17. IMPAIRED FEAR EXTINCTION ASSOCIATED WITH PTSD INCREASES WITH HOURS-SINCE-WAKING.

    PubMed

    Zuj, Daniel V; Palmer, Matthew A; Hsu, Chia-Ming K; Nicholson, Emma L; Cushing, Pippa J; Gray, Kate E; Felmingham, Kim L

    2016-03-01

    Prior research has demonstrated that time-of-day may play an important role in the extinction of conditioned fear, with extinction better learned earlier in the day rather than later. Impaired fear extinction memory is widely considered a key mechanism of posttraumatic stress disorder (PTSD). The relationship between fear extinction and PTSD symptoms may be moderated by hours-since-waking. In the present experiment, we examined whether hours-since-waking would moderate fear extinction learning ability in a clinical PTSD sample (n = 15), compared to trauma-exposed (n = 33) and nonexposed controls (n = 22). Participants completed a standardized differential fear conditioning and extinction paradigm, providing skin conductance response measures to quantify conditioned responding. Mixed-model analysis of variance revealed a PTSD-specific impairment in extinction learning ability in the late extinction phase. A moderation analysis showed that hours-since-waking was a significant moderator of the relationship between impaired late extinction and PTSD symptoms. Specifically, we found that participants with higher PTSD symptoms demonstrated poorer fear extinction learning ability as they were awake for longer. The results of the current study add to a growing literature indicating deficits in fear extinction learning in PTSD samples, compared to trauma-exposed and nonexposed controls. These results support previous findings that fear extinction is impaired later in the day, and extends this to a clinical sample, suggesting that exposure-therapy may be optimized by scheduling sessions in the morning. © 2016 Wiley Periodicals, Inc.

  18. Body size and extinction risk in terrestrial mammals above the species level.

    PubMed

    Tomiya, Susumu

    2013-12-01

    Mammalian body mass strongly correlates with life history and population properties at the scale of mouse to elephant. Large body size is thus often associated with elevated extinction risk. I examined the North American fossil record (28-1 million years ago) of 276 terrestrial genera to uncover the relationship between body size and extinction probability above the species level. Phylogenetic comparative analysis revealed no correlation between sampling-adjusted durations and body masses ranging 7 orders of magnitude, an observation that was corroborated by survival analysis. Most of the ecological and temporal groups within the data set showed the same lack of relationship. Size-biased generic extinctions do not constitute a general feature of the Holarctic mammalian faunas in the Neogene. Rather, accelerated loss of large mammals occurred during intervals that experienced combinations of regional aridification and increased biomic heterogeneity within continents. The latter phenomenon is consistent with the macroecological prediction that large geographic ranges are critical to the survival of large mammals in evolutionary time. The frequent lack of size selectivity in generic extinctions can be reconciled with size-biased species loss if extinctions of large and small mammals at the species level are often driven by ecological perturbations of different spatial and temporal scales, while those at the genus level are more synchronized in time as a result of fundamental, multiscale environmental shifts.

  19. Carbonate "Clumped" Isotope Determination of Seawater Temperature During the End-Triassic Extinction Event

    NASA Astrophysics Data System (ADS)

    Gammariello, R. T., Jr.; Petryshyn, V. A.; Ibarra, Y.; Greene, S. E.; Corsetti, F. A.; Bottjer, D. J.; Tripati, A.

    2014-12-01

    Stromatolites are laminated sedimentary structures that are commonly thought to be created by cyanobacteria, either through the trapping and binding of sediment, or through metabolically-induced precipitation. However, stromatolite formation is poorly understood. In general, stromatolite abundance was higher in the Proterozoic than the Phanerozoic, but notable increases in stromatolite abundance occur in association with Phanerozoic mass extinction events. Here, we focus on stromatolites from the latest Triassic Cotham Marble (United Kingdom) that are associated with the extinction interval. The end-Triassic mass extinction is coincident with large-scale volcanism in the Central Atlantic Magmatic Province (CAMP) and the associated breakup of Pangea. Some hypothesize that CAMP-associated increases in atmospheric CO2 led to a rise in global temperatures and ocean acidification that caused or enhanced the extinction. In order to quantify the role of climate change with respect to the end-Triassic mass extinction, we applied the carbonate "clumped" isotope paleothermometer to the well-preserved Cotham Marble stromatolites. The stromatolites were deposited in the shallow Tethys Sea, and today occur in several localities across the southwestern UK. The stromatolites alternate on the cm scale between laminated and dendrolitic microstructures and each was microdrilled for clumped isotope analysis. The two microstructures display different temperatures of formation, where the dendrolitic portions apparently grew under cooler conditions than laminated layers, and younger layers grew in cooler conditions than older layers. Our results suggest that temperature fluctuated and potentially trended towards amelioration of the warm temperatures during the deposition of the Cotham Marble.

  20. VizieR Online Data Catalog: Arches cluster: IR phot., extinction and masses (Habibi+, 2013)

    NASA Astrophysics Data System (ADS)

    Habibi, M.; Stolte, A.; Brandner, W.; Hussmann, B.; Motohara, K.

    2013-05-01

    We observed the Arches cluster out to its tidal radius using Ks-band and H-band imaging obtained on June 6-10 2008 with NAOS/CONICA at the VLT combined with Subaro/Cisco J-band data to gain a full understanding of the cluster mass distribution. The acquired Ks-band images cover four fields of 27.8*27.8(arcsec) each, provided by the medium resolution camera (S27) with a pixel scale of 0.027(arcsec). During the Ks-band observations, the natural visual seeing varied from 0.61" to 0.98". We achieved typical spatial resolutions of 0.081-0.135(arcsec) on individual frames using this AO setup. Seeing-limited J-band observations, on July 17, 2000, were performed with the CISCO spectrograph and camera which provided a pixel scale of 0.116(arcsec) and a field of view of 2*2(arcmin). An average seeing of 0.49(arcsec) resulted into a Full Width at Half Maximum (FWHM) of the point-spread function (PSF) of 0.39(arcsec) on the combined image. The catalogue includes derived infrared-photometry in J, H and Ks bands as well as derived individual extinction value and stellar masses. We used the NAOS-CONICA observations obtained in March 2002 in the central part of the Arches cluster to cover the whole cluster area. (1 data file).

  1. Mobility of iridium in terrestrial environments: Implications for the interpretation of impact-related mass-extinctions

    NASA Astrophysics Data System (ADS)

    Martín-Peinado, F. J.; Rodríguez-Tovar, F. J.

    2010-08-01

    Traditionally, iridium has been considered an element of low mobility, but its behavior is still debated. Ir concentration in a soil affected by a catastrophic mining spill in 1998 that covered the soil with a layer of tailings offers the opportunity to analyse an exceptional Ir-bearing horizon 10 years after deposition. This has enabled comparisons with the values of past Ir-bearing horizons associated to impact-related mass-extinction events. Iridium concentration in the tailings (0.349 ppm) was 5-fold higher than the anomaly in the K-Pg at The Moody Creek Mine section (the highest values obtained from terrestrial sections). The oxidative weathering of the tailings caused the release of Ir and infiltration into the soil. Iridium distribution in depth indicates redistribution throughout the profile in relation to the change in the physico-chemical properties of the soil. With regard to the background concentration in the soil (0.056 ppm), anomalous values of Ir (0.129 ppm) can be detected to 11 cm below the layer of tailings. The correlation analysis between the Ir concentration and the main properties and constituents of the soils indicated a significant correlation with sulfur, iron, clay content, and pH. Selective extractions were made to study the forms in which Ir can be mobilized in the soil. The residual/insoluble fraction was >90% of the total Ir concentration in soil. Soluble-in-water concentration of Ir (1.5% of total) was detected in the uppermost 2-3 cm of the soil, which were directly affected by the leaching of acidic waters coming from the oxidation of the pyrite tailings. Iridium retention in the affected part of the soil reached 9% of the total Ir concentration; this retention could be related to the amorphous iron forms dissolved by the oxalic-oxalate extraction. However, according to our research, original Ir abundance could be secondarily modified, and then a direct analysis of the iridium values recorded in sediments could induce

  2. Neurocircuitry of fear extinction in adult and juvenile rats.

    PubMed

    Ganella, Despina E; Nguyen, Ly Dao; Lee-Kardashyan, Luba; Kim, Leah E; Paolini, Antonio G; Kim, Jee Hyun

    2018-06-10

    In contrast to adult rodents, juvenile rodents fail to show relapse following extinction of conditioned fear. Using different retrograde tracers injected into the infralimbic cortex (IL) and the ventral hippocampus (vHPC) in conjunction with c-Fos and parvalbumin (PV) immunochemistry, we investigated the neurocircuitry of extinction in juvenile and adult rats. Regardless of fear extinction or retrieval, juvenile rats had more c-Fos+ neurons in the basolateral amygdala (BLA) compared to adults, and showed a higher proportion of c-Fos+ IL-projecting neurons. Adult rats had more activated vHPC-projecting BLA neurons following extinction compared to retrieval, a difference not observed in juvenile rats. The number of activated vHPC- or IL-projecting BLA neurons was significantly correlated with freezing levels in adult, but not juvenile, rats. We also identified neurons in the BLA that simultaneously project to the IL and vHPC activated in the retrieval groups at both ages. This study provides novel insight into the neural process underlying extinction, especially in the juvenile period. Copyright © 2018 Elsevier B.V. All rights reserved.

  3. Salinity changes and anoxia resulting from enhanced run-off during the late Permian global warming and mass extinction event

    NASA Astrophysics Data System (ADS)

    van Soelen, Elsbeth E.; Twitchett, Richard J.; Kürschner, Wolfram M.

    2018-04-01

    The late Permian biotic crisis had a major impact on marine and terrestrial environments. Rising CO2 levels following Siberian Trap volcanic activity were likely responsible for expanding marine anoxia and elevated water temperatures. This study focuses on one of the stratigraphically most expanded Permian-Triassic records known, from Jameson Land, East Greenland. High-resolution sampling allows for a detailed reconstruction of the changing environmental conditions during the extinction event and the development of anoxic water conditions. Since very little is known about how salinity was affected during the extinction event, we especially focus on the aquatic palynomorphs and infer changes in salinity from changes in the assemblage and morphology. The start of the extinction event, here defined by a peak in spore : pollen, indicating disturbance and vegetation destruction in the terrestrial environment, postdates a negative excursion in the total organic carbon, but predates the development of anoxia in the basin. Based on the newest estimations for sedimentation rates, the marine and terrestrial ecosystem collapse took between 1.6 and 8 kyr, a much shorter interval than previously estimated. The palynofacies and palynomorph records show that the environmental changes can be explained by enhanced run-off and increased primary productivity and water column stratification. A lowering in salinity is supported by changes in the acritarch morphology. The length of the processes of the acritarchs becomes shorter during the extinction event and we propose that these changes are evidence for a reduction in salinity in the shallow marine setting of the study site. This inference is supported by changes in acritarch distribution, which suggest a change in palaeoenvironment from open marine conditions before the start of the extinction event to more nearshore conditions during and after the crisis. In a period of sea-level rise, such a reduction in salinity can only be

  4. Attenuating fearful memories: effect of cued extinction on intrusions.

    PubMed

    Marks, Elizabeth H; Zoellner, Lori A

    2014-12-01

    Exposure-based therapies for posttraumatic stress disorder are thought to reduce intrusive memories through extinction processes. Methods that enhance extinction may translate to improved treatment. Rat research suggests retrieving a memory via a conditioned stimulus (CS) cue, and then modifying the retrieved memory within a specific reconsolidation window may enhance extinction. In humans, studies (e.g., Kindt & Soeter, 2013; Schiller et al., 2010) using basic learning paradigms show discrepant findings. Using a distressing film paradigm, participants (N = 148) completed fear acquisition and extinction. At extinction, they were randomized to 1 of 3 groups: CS cue within reconsolidation window, CS cue outside window, or non-CS cue within window. Intrusions were assessed 24 hr after extinction. Participants receiving the CS cue and completing extinction within the reconsolidation window had more intrusions (M = 2.40, SD = 2.54) than those cued outside (M = 1.65, SD = 1.70) or those receiving a non-CS cue (M = 1.24, SD = 1.26), F(2, 145) = 4.52, p = .01, d = 0.55. Consistent with the reconsolidation hypothesis, presenting a CS cue does appear to activate a specific period of time during which a memory can be updated. However, the CS cue caused increased, rather than decreased, frequency of intrusions. Understanding parameters of preextinction cueing may help us better understand reconsolidation as a potential memory updating mechanism.

  5. Enhanced THz extinction in arrays of resonant semiconductor particles.

    PubMed

    Schaafsma, Martijn C; Georgiou, Giorgos; Rivas, Jaime Gómez

    2015-09-21

    We demonstrate experimentally the enhanced THz extinction by periodic arrays of resonant semiconductor particles. This phenomenon is explained in terms of the radiative coupling of localized resonances with diffractive orders in the plane of the array (Rayleigh anomalies). The experimental results are described by numerical calculations using a coupled dipole model and by Finite-Difference in Time-Domain simulations. An optimum particle size for enhancing the extinction efficiency of the array is found. This optimum is determined by the frequency detuning between the localized resonances in the individual particles and the Rayleigh anomaly. The extinction calculations and measurements are also compared to near-field simulations illustrating the optimum particle size for the enhancement of the near-field.

  6. A new stem group echinoid from the Triassic of China leads to a revised macroevolutionary history of echinoids during the end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Thompson, Jeffrey R.; Hu, Shi-xue; Zhang, Qi-Yue; Petsios, Elizabeth; Cotton, Laura J.; Huang, Jin-Yuan; Zhou, Chang-yong; Wen, Wen; Bottjer, David J.

    2018-01-01

    The Permian-Triassic bottleneck has long been thought to have drastically altered the course of echinoid evolution, with the extinction of the entire echinoid stem group having taken place during the end-Permian mass extinction. The Early Triassic fossil record of echinoids is, however, sparse, and new fossils are paving the way for a revised interpretation of the evolutionary history of echinoids during the Permian-Triassic crisis and Early Mesozoic. A new species of echinoid, Yunnanechinus luopingensis n. sp. recovered from the Middle Triassic (Anisian) Luoping Biota fossil Lagerstätte of South China, displays morphologies that are not characteristic of the echinoid crown group. We have used phylogenetic analyses to further demonstrate that Yunnanechinus is not a member of the echinoid crown group. Thus a clade of stem group echinoids survived into the Middle Triassic, enduring the global crisis that characterized the end-Permian and Early Triassic. Therefore, stem group echinoids did not go extinct during the Palaeozoic, as previously thought, and appear to have coexisted with the echinoid crown group for at least 23 million years. Stem group echinoids thus exhibited the Lazarus effect during the latest Permian and Early Triassic, while crown group echinoids did not.

  7. Allee effect in the selection for prime-numbered cycles in periodical cicadas.

    PubMed

    Tanaka, Yumi; Yoshimura, Jin; Simon, Chris; Cooley, John R; Tainaka, Kei-ichi

    2009-06-02

    Periodical cicadas are well known for their prime-numbered life cycles (17 and 13 years) and their mass periodical emergences. The origination and persistence of prime-numbered cycles are explained by the hybridization hypothesis on the basis of their lower likelihood of hybridization with other cycles. Recently, we showed by using an integer-based numerical model that prime-numbered cycles are indeed selected for among 10- to 20-year cycles. Here, we develop a real-number-based model to investigate the factors affecting the selection of prime-numbered cycles. We include an Allee effect in our model, such that a critical population size is set as an extinction threshold. We compare the real-number models with and without the Allee effect. The results show that in the presence of an Allee effect, prime-numbered life cycles are most likely to persist and to be selected under a wide range of extinction thresholds.

  8. Human influence on distribution and extinctions of the late Pleistocene Eurasian megafauna.

    PubMed

    Pushkina, Diana; Raia, Pasquale

    2008-06-01

    Late Pleistocene extinctions are of interest to paleontological and anthropological research. In North America and Australia, human occupation occurred during a short period of time and overexploitation may have led to the extinction of mammalian megafauna. In northern Eurasia megafaunal extinctions are believed to have occurred over a relatively longer period of time, perhaps as a result of changing environmental conditions, but the picture is much less clear. To consider megafaunal extinction in Eurasia, we compare differences in the geographical distribution and commonness of extinct and extant species between paleontological and archaeological localities from the late middle Pleistocene to Holocene. Purely paleontological localities, as well as most extinct species, were distributed north of archaeological sites and of the extant species, suggesting that apart from possible differences in adaptations between humans and other species, humans could also have a detrimental effect on large mammal distribution. However, evidence for human overexploitation applies only to the extinct steppe bison Bison priscus. Other human-preferred species survive into the Holocene, including Rangifer tarandus, Equus ferus, Capreolus capreolus, Cervus elaphus, Equus hemionus, Saiga tatarica, and Sus scrofa. Mammuthus primigenius and Megaloceros giganteus were rare in archaeological sites. Carnivores appear little influenced by human presence, although they become rarer in Holocene archaeological sites. Overall, the data are consistent with the conclusion that humans acted as efficient hunters selecting for the most abundant species. Our study supports the idea that the late Pleistocene extinctions were environmentally driven by climatic changes that triggered habitat fragmentation, species range reduction, and population decrease, after which human interference either by direct hunting or via indirect activities probably became critical.

  9. Estimation of Apollo Lunar Dust Transport using Optical Extinction Measurements

    NASA Astrophysics Data System (ADS)

    Lane, John E.; Metzger, Philip T.

    2015-04-01

    A technique to estimate mass erosion rate of surface soil during landing of the Apollo Lunar Module (LM) and total mass ejected due to the rocket plume interaction is proposed and tested. The erosion rate is proportional to the product of the second moment of the lofted particle size distribution N(D), and third moment of the normalized soil size distribution S(D), divided by the integral of S(D)ṡD2/v(D), where D is particle diameter and v(D) is the vertical component of particle velocity. The second moment of N(D) is estimated by optical extinction analysis of the Apollo cockpit video. Because of the similarity between mass erosion rate of soil as measured by optical extinction and rainfall rate as measured by radar reflectivity, traditional NWS radar/rainfall correlation methodology can be applied to the lunar soil case where various S(D) models are assumed corresponding to specific lunar sites.

  10. The extinction context enables extinction performance after a change in context

    PubMed Central

    Nelson, James Byron; Gregory, Pamela; Sanjuan, Maria del Carmen

    2012-01-01

    One experiment with human participants determined the extent to which recovery of extinguished responding with a context switch was due to a failure to retrieve contextually-controlled learning, or some other process such as participants learning that context changes signal reversals in the meaning of stimulus – outcome relationships. In a video game, participants learned to suppress mouse clicking in the presence of a stimulus that predicted an attack. Then, that stimulus underwent extinction in a different context (environment within the game). Following extinction, suppression was recovered and then extinguished again during testing in the conditioning context. In a final test, participants that were tested in the context where extinction first took place showed less of a recovery than those tested in a neutral context, but they showed a recovery of suppression nevertheless. A change in context tended to cause a change in the meaning of the stimulus, leading to recovery in both the neutral and extinction contexts. The extinction context attenuated that recovery, perhaps by enabling retrieval of the learning that took place in extinction. Recovery outside an extinction context is due to a failure of the context to enable the learning acquired during extinction, but only in part. PMID:22521549

  11. The Optical-Mid-infrared Extinction Law of the l = 165° Sightline in the Galactic Plane: Diversity of the Extinction Law in the Diffuse Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Wang, Shu; Jiang, B. W.; Zhao, He; Chen, Xiaodian; de Grijs, Richard

    2017-10-01

    Understanding the effects of dust extinction is important to properly interpret observations. The optical total-to-selective extinction ratio, {R}V={A}V/E(B-V), is widely used to describe extinction variations in ultraviolet and optical bands. Since the {R}V=3.1 extinction curve adequately represents the average extinction law of diffuse regions in the Milky Way, it is commonly used to correct observational measurements along sightlines toward diffuse regions in the interstellar medium. However, the {R}V value may vary even along different diffuse interstellar medium sightlines. In this paper, we investigate the optical-mid-infrared (mid-IR) extinction law toward a very diffuse region at l=165^\\circ in the Galactic plane, which was selected based on a CO emission map. Adopting red clump stars as extinction tracers, we determine the optical-mid-IR extinction law for our diffuse region in two APASS bands (B,V), three XSTPS-GAC bands (g,r,I), three 2MASS bands (J,H,{K}s), and two WISE bands (W1,W2). Specifically, 18 red clump stars were selected from the APOGEE-RC catalog based on spectroscopic data in order to explore the diversity of the extinction law. We find that the optical extinction curves exhibit appreciable diversity. The corresponding {R}V ranges from 1.7 to 3.8, while the mean {R}V value of 2.8 is consistent with the widely adopted average value of 3.1 for Galactic diffuse clouds. There is no apparent correlation between {R}V value and color excess E(B-V) in the range of interest, from 0.2 to 0.6 mag, or with specific visual extinction per kiloparsec, {A}V/d.

  12. Into the Darkness: Interstellar Extinction Near the Cepheus OB3 Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, Edward L.; Jacklin, S.; Massa, D.

    2014-01-01

    We present the results of a followup investigation to a study performed by Massa and Savage (1984, ApJ, 279, 310) of the properties of UV interstellar extinction in the region of the Cepheus OB3 molecular cloud. That study was performed using UV photometry and spectro-photometry from the ANS and IUE satellites. We have extended this study into the IR, utilizing the uniform database of IR photometry available from the 2MASS project. This is a part of a larger program whose goal is to study the properties of extinction in localized regions, where we hope to find clues to dust grain growth and destruction processes through spatial correlations of extinction with distinct environmental properties. Similarly to Massa and Savage’s UV results, we find that the IR extinction properties on the Cepheus OB3 region vary systematically with the apparent proximity of the target stars to the molecular cloud. We also find that the UV extinction and the IR extinction are crudely correlated. The methodology leading to these results and their implications are discussed.

  13. Changing palaeoenvironments and tetrapod populations in the Daptocephalus Assemblage Zone (Karoo Basin, South Africa) indicate early onset of the Permo-Triassic mass extinction

    NASA Astrophysics Data System (ADS)

    Viglietti, Pia A.; Smith, Roger M. H.; Rubidge, Bruce S.

    2018-02-01

    Important palaeoenvironmental differences are identified during deposition of the latest Permian Daptocephalus Assemblage Zone (DaAZ) of the South African Beaufort Group (Karoo Supergoup), which is also divided into a Lower and Upper subzone. A lacustrine floodplain facies association showing evidence for higher water tables and subaqueous conditions on the floodplains is present in Lower DaAZ. The change to well-drained floodplain facies association in the Upper DaAZ is coincident with a faunal turnover as evidenced by the last appearance of the dicynodont Dicynodon lacerticeps, the therocephalian Theriognathus microps, the cynodont Procynosuchus delaharpeae, and first appearance of the dicynodont Lystrosaurus maccaigi within the Ripplemead member. Considering the well documented 3-phased extinction of Karoo tetrapods during the Permo-Triassic Mass Extinction (PTME), the facies transition between the Lower and Upper DaAZ represents earlier than previously documented palaeoenvironmental changes associated with the onset of this major global biotic crisis.

  14. Local extinction of a coral reef fish explained by inflexible prey choice

    NASA Astrophysics Data System (ADS)

    Brooker, R. M.; Munday, P. L.; Brandl, S. J.; Jones, G. P.

    2014-12-01

    While global extinctions of marine species are infrequent, local extinctions are becoming common. However, the role of habitat degradation and resource specialisation in explaining local extinction is unknown. On coral reefs, coral bleaching is an increasingly frequent cause of coral mortality that can result in dramatic changes to coral community composition. Coral-associated fishes are often specialised on a limited suite of coral species and are therefore sensitive to these changes. This study documents the local extinction of a corallivorous reef fish, Oxymonacanthus longirostris, following a mass bleaching event that altered the species composition of associated coral communities. Local extinction only occurred on reefs that also completely lost a key prey species, Acropora millepora, even though coral cover remained high. In an experimental test, fish continued to select bleached A. millepora over the healthy, but less-preferred prey species that resisted bleaching. These results suggest that behavioural inflexibility may limit the ability of specialists to cope with even subtle changes to resource availability.

  15. Sleep supports cued fear extinction memory consolidation independent of circadian phase.

    PubMed

    Melo, Irene; Ehrlich, Ingrid

    2016-07-01

    Sleep promotes memory, particularly for declarative learning. However, its role in non-declarative, emotional memories is less well understood. Some studies suggest that sleep may influence fear-related memories, and thus may be an important factor determining the outcome of treatments for emotional disorders such as post-traumatic stress disorder. Here, we investigated the effect of sleep deprivation and time of day on fear extinction memory consolidation. Mice were subjected to a cued Pavlovian fear and extinction paradigm at the beginning of their resting or active phase. Immediate post-extinction learning sleep deprivation for 5h compromised extinction memory when tested 24h after learning. Context-dependent extinction memory recall was completely prevented by sleep-manipulation during the resting phase, while impairment was milder during the active phase and extinction memory retained its context-specificity. Importantly, control experiments excluded confounding factors such as differences in baseline locomotion, fear generalization and stress hormone levels. Together, our findings indicate that post-learning sleep supports cued fear extinction memory consolidation in both circadian phases. The lack of correlation between memory efficacy and sleep time suggests that extinction memory may be influenced by specific sleep events in the early consolidation period. Copyright © 2016 Elsevier Inc. All rights reserved.

  16. Prelude of benthic community collapse during the end-Permian mass extinction in siliciclastic offshore sub-basin: Brachiopod evidence from South China

    NASA Astrophysics Data System (ADS)

    Wu, Huiting; He, Weihong; Weldon, Elizabeth A.

    2018-04-01

    Analysis of the Permian-Triassic palaeocommunities from basinal facies in South China provides an insight into the environmental deterioration occurring in the prelude to the mass extinction event. Quantitative and multivariate analyses on three brachiopod palaeocommunities from the Changhsingian to the earliest Triassic in basinal facies in South China have been undertaken in this study. Although the end-Permian extinction has been proved to be a one-stepped event, ecological warning signals appeared in the palaeocommunities long before the main pulse of the event. A brachiopod palaeocommunity turnover occurred in the upper part of the Clarkina changxingensis Zone, associated with a significant decrease of palaeocommunity diversity and brachiopod body size. During this turnover the dominant genera changed from Fusichonetes and Crurithyris (or/and Paracrurithyris) to the more competitive genus Crurithyris (or/and Paracrurithyris). The brachiopod palaeocommunity turnover was supposed to be triggered by the decreased marine primary productivity and increased volcanic activity. Moreover, such early warning signals are found not only in the deep-water siliceous facies, but also in the shallow-water clastic facies and carbonate rock facies in South China.

  17. A Statistical Test of Correlations and Periodicities in the Geological Records

    NASA Astrophysics Data System (ADS)

    Yabushita, S.

    1997-09-01

    Matsumoto & Kubotani argued that there is a positive and statistically significant correlation between cratering and mass extinction. This argument is critically examined by adopting a method of Ertel used by Matsumoto & Kubotani but by applying it more directly to the extinction and cratering records. It is shown that on the null-hypothesis of random distribution of crater ages, the observed correlation has a probability of occurrence of 13%. However, when large craters are excluded whose ages agree with the times of peaks of extinction rate of marine fauna, one obtains a negative correlation. This result strongly indicates that mass extinction are not due to accumulation of impacts but due to isolated gigantic impacts.

  18. Profitless delays for extinction in nonautonomous Lotka-Volterra system

    NASA Astrophysics Data System (ADS)

    Liu, Shengqiang; Chen, Lansun

    2001-12-01

    We study the delayed periodic n-species Lotka-Voterra systems where the growth rate of each species is not always positive. The sufficient conditions for the extinction that are independent of the delays are obtained. Some known results are improved and generalized. Our results suggest that under some conditions, the introduction and the variance of the time delays can be both harmless and profitless. Discussion about the effect of time delays on the extinction of the system is also advanced.

  19. Selecting for extinction: nonrandom disease-associated extinction homogenizes amphibian biotas.

    PubMed

    Smith, Kevin G; Lips, Karen R; Chase, Jonathan M

    2009-10-01

    Studying the patterns in which local extinctions occur is critical to understanding how extinctions affect biodiversity at local, regional and global spatial scales. To understand the importance of patterns of extinction at a regional spatial scale, we use data from extirpations associated with a widespread pathogenic agent of amphibian decline, Batrachochytrium dendrobatidis (Bd) as a model system. We apply novel null model analyses to these data to determine whether recent extirpations associated with Bd have resulted in selective extinction and homogenization of diverse tropical American amphibian biotas. We find that Bd-associated extinctions in this region were nonrandom and disproportionately, but not exclusively, affected low-occupancy and endemic species, resulting in homogenization of the remnant amphibian fauna. The pattern of extirpations also resulted in phylogenetic homogenization at the family level and ecological homogenization of reproductive mode and habitat association. Additionally, many more species were extirpated from the region than would be expected if extirpations occurred randomly. Our results indicate that amphibian declines in this region are an extinction filter, reducing regional amphibian biodiversity to highly similar relict assemblages and ultimately causing amplified biodiversity loss at regional and global scales.

  20. Radiocarbon dating of extinct fauna in the Americas recovered from tar pits

    NASA Astrophysics Data System (ADS)

    Jull, A. J. T.; Iturralde-Vinent, M.; O'Malley, J. M.; MacPhee, R. D. E.; McDonald, H. G.; Martin, P. S.; Moody, J.; Rincón, A.

    2004-08-01

    We have obtained radiocarbon dates by accelerator mass spectrometry on bones of extinct large mammals from tar pits. Results on some samples of Glyptodon and Holmesina (extinct large mammals similar to armadillos) yielded ages of >25 and >21 ka, respectively. We also studied the radiocarbon ages of three different samples of bones from the extinct Cuban ground sloth, Parocnus bownii, which yielded dates ranging from 4960 ± 280 to 11 880 ± 420 yr BP. In order to remove the tar component pretreat the samples sufficiently to obtain reliable dates, we cleaned the samples by Soxhlet extraction in benzene. Resulting samples of collagenous material were often small.

  1. Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development.

    PubMed

    Erickson, Gregory M; Zelenitsky, Darla K; Kay, David Ian; Norell, Mark A

    2017-01-17

    Birds stand out from other egg-laying amniotes by producing relatively small numbers of large eggs with very short incubation periods (average 11-85 d). This aspect promotes high survivorship by limiting exposure to predation and environmental perturbation, allows for larger more fit young, and facilitates rapid attainment of adult size. Birds are living dinosaurs; their rapid development has been considered to reflect the primitive dinosaurian condition. Here, nonavian dinosaurian incubation periods in both small and large ornithischian taxa are empirically determined through growth-line counts in embryonic teeth. Our results show unexpectedly slow incubation (2.8 and 5.8 mo) like those of outgroup reptiles. Developmental and physiological constraints would have rendered tooth formation and incubation inherently slow in other dinosaur lineages and basal birds. The capacity to determine incubation periods in extinct egg-laying amniotes has implications for dinosaurian embryology, life history strategies, and survivorship across the Cretaceous-Paleogene mass extinction event.

  2. Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development

    PubMed Central

    Erickson, Gregory M.; Zelenitsky, Darla K.; Kay, David Ian; Norell, Mark A.

    2017-01-01

    Birds stand out from other egg-laying amniotes by producing relatively small numbers of large eggs with very short incubation periods (average 11–85 d). This aspect promotes high survivorship by limiting exposure to predation and environmental perturbation, allows for larger more fit young, and facilitates rapid attainment of adult size. Birds are living dinosaurs; their rapid development has been considered to reflect the primitive dinosaurian condition. Here, nonavian dinosaurian incubation periods in both small and large ornithischian taxa are empirically determined through growth-line counts in embryonic teeth. Our results show unexpectedly slow incubation (2.8 and 5.8 mo) like those of outgroup reptiles. Developmental and physiological constraints would have rendered tooth formation and incubation inherently slow in other dinosaur lineages and basal birds. The capacity to determine incubation periods in extinct egg-laying amniotes has implications for dinosaurian embryology, life history strategies, and survivorship across the Cretaceous–Paleogene mass extinction event. PMID:28049837

  3. Climate change not to blame for late Quaternary megafauna extinctions in Australia

    PubMed Central

    Saltré, Frédérik; Rodríguez-Rey, Marta; Brook, Barry W.; Johnson, Christopher N; Turney, Chris S. M.; Alroy, John; Cooper, Alan; Beeton, Nicholas; Bird, Michael I.; Fordham, Damien A.; Gillespie, Richard; Herrando-Pérez, Salvador; Jacobs, Zenobia; Miller, Gifford H.; Nogués-Bravo, David; Prideaux, Gavin J.; Roberts, Richard G.; Bradshaw, Corey J. A.

    2016-01-01

    Late Quaternary megafauna extinctions impoverished mammalian diversity worldwide. The causes of these extinctions in Australia are most controversial but essential to resolve, because this continent-wide event presaged similar losses that occurred thousands of years later on other continents. Here we apply a rigorous metadata analysis and new ensemble-hindcasting approach to 659 Australian megafauna fossil ages. When coupled with analysis of several high-resolution climate records, we show that megafaunal extinctions were broadly synchronous among genera and independent of climate aridity and variability in Australia over the last 120,000 years. Our results reject climate change as the primary driver of megafauna extinctions in the world's most controversial context, and instead estimate that the megafauna disappeared Australia-wide ∼13,500 years after human arrival, with shorter periods of coexistence in some regions. This is the first comprehensive approach to incorporate uncertainty in fossil ages, extinction timing and climatology, to quantify mechanisms of prehistorical extinctions. PMID:26821754

  4. Extinction and recolonization of coastal megafauna following human arrival in New Zealand.

    PubMed

    Collins, Catherine J; Rawlence, Nicolas J; Prost, Stefan; Anderson, Christian N K; Knapp, Michael; Scofield, R Paul; Robertson, Bruce C; Smith, Ian; Matisoo-Smith, Elizabeth A; Chilvers, B Louise; Waters, Jonathan M

    2014-07-07

    Extinctions can dramatically reshape biological communities. As a case in point, ancient mass extinction events apparently facilitated dramatic new evolutionary radiations of surviving lineages. However, scientists have yet to fully understand the consequences of more recent biological upheaval, such as the megafaunal extinctions that occurred globally over the past 50 kyr. New Zealand was the world's last large landmass to be colonized by humans, and its exceptional archaeological record documents a vast number of vertebrate extinctions in the immediate aftermath of Polynesian arrival approximately AD 1280. This recently colonized archipelago thus presents an outstanding opportunity to test for rapid biological responses to extinction. Here, we use ancient DNA (aDNA) analysis to show that extinction of an endemic sea lion lineage (Phocarctos spp.) apparently facilitated a subsequent northward range expansion of a previously subantarctic-limited lineage. This finding parallels a similar extinction-replacement event in penguins (Megadyptes spp.). In both cases, an endemic mainland clade was completely eliminated soon after human arrival, and then replaced by a genetically divergent clade from the remote subantarctic region, all within the space of a few centuries. These data suggest that ecological and demographic processes can play a role in constraining lineage distributions, even for highly dispersive species, and highlight the potential for dynamic biological responses to extinction. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  5. Mass loss during the RR Lyrae phase of the horizontal branch: Mass dispersion on the horizontal branch and RR Lyrae period changes

    NASA Technical Reports Server (NTRS)

    Koopmann, Rebecca A.; Lee, Young-Wook; Demarque, Pierre; Howard, Jamie M.

    1994-01-01

    Mass loss on the horizontal branch has been invoked in the literature to explain such phenomena as the color (mass) dispersion of the horizontal branch and the observed distribution of period changes in RR Lyrae stars. To test these claims, the Yale stellar evolution code was used to evolve horizontal branch models of masses 0.64, 0.66, 0.68, 0.70, and 0.72 solar mass with Z of 0.001, core mass of 0.4893, main-sequence helium abundance of 0.23, and constant mass loss rates of 0, 10(exp -10), 5 x 10(exp -10), and 10(exp -9) solar mass/yr. Mass loss was assumed to occur only in the instability strip, where a mechanism is most likely to exist. Synthetic horizontal branches, constructed from the models, show that mass loss on the horizontal branch cannot produce the observed color dispersion even for the highest mass-loss rate of 10(exp -9) solar mass/yr. Mass loss is unlikely to occur at a higher rate without significant effects on the horizontal branch morphology, which would destroy the good agreement between standard synthetic models without mass loss and observed horizontal branches. Periods and period changes were calculated for all models. The period changes are not significantly larger for models with mass loss. The effect of mass loss in clusters of other metallicities is discussed.

  6. Seed Dispersal Anachronisms: Rethinking the Fruits Extinct Megafauna Ate

    PubMed Central

    Guimarães, Paulo R.; Galetti, Mauro; Jordano, Pedro

    2008-01-01

    Background Some neotropical, fleshy-fruited plants have fruits structurally similar to paleotropical fruits dispersed by megafauna (mammals >103 kg), yet these dispersers were extinct in South America 10–15 Kyr BP. Anachronic dispersal systems are best explained by interactions with extinct animals and show impaired dispersal resulting in altered seed dispersal dynamics. Methodology/Principal Findings We introduce an operational definition of megafaunal fruits and perform a comparative analysis of 103 Neotropical fruit species fitting this dispersal mode. We define two megafaunal fruit types based on previous analyses of elephant fruits: fruits 4–10 cm in diameter with up to five large seeds, and fruits >10 cm diameter with numerous small seeds. Megafaunal fruits are well represented in unrelated families such as Sapotaceae, Fabaceae, Solanaceae, Apocynaceae, Malvaceae, Caryocaraceae, and Arecaceae and combine an overbuilt design (large fruit mass and size) with either a single or few (<3 seeds) extremely large seeds or many small seeds (usually >100 seeds). Within-family and within-genus contrasts between megafaunal and non-megafaunal groups of species indicate a marked difference in fruit diameter and fruit mass but less so for individual seed mass, with a significant trend for megafaunal fruits to have larger seeds and seediness. Conclusions/Significance Megafaunal fruits allow plants to circumvent the trade-off between seed size and dispersal by relying on frugivores able to disperse enormous seed loads over long-distances. Present-day seed dispersal by scatter-hoarding rodents, introduced livestock, runoff, flooding, gravity, and human-mediated dispersal allowed survival of megafauna-dependent fruit species after extinction of the major seed dispersers. Megafauna extinction had several potential consequences, such as a scale shift reducing the seed dispersal distances, increasingly clumped spatial patterns, reduced geographic ranges and limited genetic

  7. Ecomorphological selectivity among marine teleost fishes during the end-Cretaceous extinction

    PubMed Central

    Friedman, Matt

    2009-01-01

    Despite the attention focused on mass extinction events in the fossil record, patterns of extinction in the dominant group of marine vertebrates—fishes—remain largely unexplored. Here, I demonstrate ecomorphological selectivity among marine teleost fishes during the end-Cretaceous extinction, based on a genus-level dataset that accounts for lineages predicted on the basis of phylogeny but not yet sampled in the fossil record. Two ecologically relevant anatomical features are considered: body size and jaw-closing lever ratio. Extinction intensity is higher for taxa with large body sizes and jaws consistent with speed (rather than force) transmission; resampling tests indicate that victims represent a nonrandom subset of taxa present in the final stage of the Cretaceous. Logistic regressions of the raw data reveal that this nonrandom distribution stems primarily from the larger body sizes of victims relative to survivors. Jaw mechanics are also a significant factor for most dataset partitions but are always less important than body size. When data are corrected for phylogenetic nonindependence, jaw mechanics show a significant correlation with extinction risk, but body size does not. Many modern large-bodied, predatory taxa currently suffering from overexploitation, such billfishes and tunas, first occur in the Paleocene, when they appear to have filled the functional space vacated by some extinction victims. PMID:19276106

  8. Ecomorphological selectivity among marine teleost fishes during the end-Cretaceous extinction.

    PubMed

    Friedman, Matt

    2009-03-31

    Despite the attention focused on mass extinction events in the fossil record, patterns of extinction in the dominant group of marine vertebrates-fishes-remain largely unexplored. Here, I demonstrate ecomorphological selectivity among marine teleost fishes during the end-Cretaceous extinction, based on a genus-level dataset that accounts for lineages predicted on the basis of phylogeny but not yet sampled in the fossil record. Two ecologically relevant anatomical features are considered: body size and jaw-closing lever ratio. Extinction intensity is higher for taxa with large body sizes and jaws consistent with speed (rather than force) transmission; resampling tests indicate that victims represent a nonrandom subset of taxa present in the final stage of the Cretaceous. Logistic regressions of the raw data reveal that this nonrandom distribution stems primarily from the larger body sizes of victims relative to survivors. Jaw mechanics are also a significant factor for most dataset partitions but are always less important than body size. When data are corrected for phylogenetic nonindependence, jaw mechanics show a significant correlation with extinction risk, but body size does not. Many modern large-bodied, predatory taxa currently suffering from overexploitation, such billfishes and tunas, first occur in the Paleocene, when they appear to have filled the functional space vacated by some extinction victims.

  9. Linking indices for biodiversity monitoring to extinction risk theory.

    PubMed

    McCarthy, Michael A; Moore, Alana L; Krauss, Jochen; Morgan, John W; Clements, Christopher F

    2014-12-01

    Biodiversity indices often combine data from different species when used in monitoring programs. Heuristic properties can suggest preferred indices, but we lack objective ways to discriminate between indices with similar heuristics. Biodiversity indices can be evaluated by determining how well they reflect management objectives that a monitoring program aims to support. For example, the Convention on Biological Diversity requires reporting about extinction rates, so simple indices that reflect extinction risk would be valuable. We developed 3 biodiversity indices that are based on simple models of population viability that relate extinction risk to abundance. We based the first index on the geometric mean abundance of species and the second on a more general power mean. In a third index, we integrated the geometric mean abundance and trend. These indices require the same data as previous indices, but they also relate directly to extinction risk. Field data for butterflies and woodland plants and experimental studies of protozoan communities show that the indices correlate with local extinction rates. Applying the index based on the geometric mean to global data on changes in avian abundance suggested that the average extinction probability of birds has increased approximately 1% from 1970 to 2009. © 2014 The Authors. Conservation Biology published by Wiley Periodicals, Inc., on behalf of the Society for Conservation Biology.

  10. Global deep-sea extinctions during the Pleistocene ice ages

    NASA Astrophysics Data System (ADS)

    Hayward, Bruce W.

    2001-07-01

    The dark, near-freezing environment of the deep oceans is regarded as one of the most stable habitats on Earth, and this stability is generally reflected in the slow turnover rates (extinctions and appearances) of the organisms that live there. By far the best fossil record of deep-sea organisms is provided by the shells of benthic foraminifera (Protista). A little-known global extinction of deep-sea benthic foraminifera occurred during the Pleistocene ice ages. In the southwest Pacific, it caused the disappearance of at least two families, 15 genera, and 48 species (˜15% 25% of the fauna) of dominantly uniserial, elongate foraminifera with distinctive apertural modifications. These forms progressively died back and became extinct during glacial periods in the late Pliocene to middle Pleistocene (ca. 2.5 0.6 Ma); most extinctions occurred between 1.0 and 0.6 Ma, at the time of the middle Pleistocene climatic revolution. This first high-resolution study of this extinction event indicates that it was far more significant for deep-sea diversity loss than previously reported (10 species). The middle Pleistocene extinction was the most dramatic last phase of a worldwide decline in the abundance of these elongate forms, a phase that began during cooling near the Eocene-Oligocene boundary and continued during the middle Miocene. Clearly these taxa declined when the world cooled, but the reason is yet to be resolved.

  11. Estradiol shifts interactions between the infralimbic cortex and central amygdala to enhance fear extinction memory in female rats.

    PubMed

    Maeng, Lisa Y; Cover, Kara K; Taha, Mohamad B; Landau, Aaron J; Milad, Mohammed R; Lebrón-Milad, Kelimer

    2017-01-02

    There is growing evidence that estradiol (E2) enhances fear extinction memory consolidation. However, it is unclear how E2 influences the nodes of the fear extinction network to enhance extinction memory. This study begins to delineate the neural circuits underlying the influence of E2 on fear extinction acquisition and consolidation in female rats. After fear conditioning (day 1), naturally cycling female rats underwent extinction learning (day 2) in a low-E2 state, receiving a systemic administration of either E2 or vehicle prior to extinction training. Extinction memory recall was then tested 24 hr later (day 3). We measured immediate early gene c-fos expression within the extinction network during fear extinction learning and extinction recall. During extinction learning, E2 treatment increased centrolateral amygdala c-fos activity and reduced lateral amygdala activity relative to vehicle. During extinction recall, E2-treated rats exhibited reduced c-fos expression in the centromedial amygdala. There were no group differences in c-fos expression within the medial prefrontal cortex or dorsal hippocampus. Examining c-fos ratios with the infralimbic cortex (IL) revealed that, despite the lack of group differences within the IL, E2 treatment induced greater IL activity relative to both prelimbic cortex and central amygdala (CeA) activity during extinction memory recall. Only the relationship between IL and CeA activity positively correlated with extinction retention. In conclusion, E2 appears to modify interactions between the IL and the CeA in females, shifting from stronger amygdalar modulation of fear during extinction learning to stronger IL control during extinction recall. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  12. Extinction Risk and Diversification Are Linked in a Plant Biodiversity Hotspot

    PubMed Central

    Davies, T. Jonathan; Smith, Gideon F.; Bellstedt, Dirk U.; Boatwright, James S.; Bytebier, Benny; Cowling, Richard M.; Forest, Félix; Harmon, Luke J.; Muasya, A. Muthama; Schrire, Brian D.; Steenkamp, Yolande; van der Bank, Michelle; Savolainen, Vincent

    2011-01-01

    It is widely recognized that we are entering an extinction event on a scale approaching the mass extinctions seen in the fossil record. Present-day rates of extinction are estimated to be several orders of magnitude greater than background rates and are projected to increase further if current trends continue. In vertebrates, species traits, such as body size, fecundity, and geographic range, are important predictors of vulnerability. Although plants are the basis for life on Earth, our knowledge of plant extinctions and vulnerabilities is lagging. Here, we disentangle the underlying drivers of extinction risk in plants, focusing on the Cape of South Africa, a global biodiversity hotspot. By comparing Red List data for the British and South African floras, we demonstrate that the taxonomic distribution of extinction risk differs significantly between regions, inconsistent with a simple, trait-based model of extinction. Using a comprehensive phylogenetic tree for the Cape, we reveal a phylogenetic signal in the distribution of plant extinction risks but show that the most threatened species cluster within short branches at the tips of the phylogeny—opposite to trends in mammals. From analyzing the distribution of threatened species across 11 exemplar clades, we suggest that mode of speciation best explains the unusual phylogenetic structure of extinction risks in plants of the Cape. Our results demonstrate that explanations for elevated extinction risk in plants of the Cape flora differ dramatically from those recognized for vertebrates. In the Cape, extinction risk is higher for young and fast-evolving plant lineages and cannot be explained by correlations with simple biological traits. Critically, we find that the most vulnerable plant species are nonetheless marching towards extinction at a more rapid pace but, surprisingly, independently from anthropogenic effects. Our results have important implications for conservation priorities and cast doubts on the

  13. Disruption of human fear reconsolidation using imaginal and in vivo extinction.

    PubMed

    Agren, Thomas; Björkstrand, Johannes; Fredrikson, Mats

    2017-02-15

    Memories are not set forever, but can be altered following reactivation, which renders memories malleable, before they are again stabilized through reconsolidation. Fear memories can be attenuated by using extinction during the malleable period. The present study adopts a novel form of extinction, using verbal instructions, in order to examine whether fear memory reconsolidation can be affected by an imaginal exposure. The extinction using verbal instructions, called imaginal extinction, consists of a recorded voice encouraging participants to imagine the scene in which fear was acquired, and to envision the stimuli before their inner eye. The voice signals stimuli appearance, and identical to standard (in vivo) extinction, participants discover that the conditioned stimulus no longer is followed by unconditioned stimulus (UCS). In this way, imaginal extinction translates clinically used imaginal exposure into the standard experimental fear conditioning paradigm. Fear was acquired by pairing pictorial stimuli with an electric shock UCS. Then, both standard and imaginal extinction were given following fear memory reactivation, either after 10min, within the reconsolidation interval, or after 6h, outside of the reconsolidation interval. In vivo and imaginal extinction produced comparable reductions in conditioned responses during extinction and importantly, both disrupted reconsolidation of conditioned fear and abolished stimulus discrimination between reinforced and non-reinforced cues. Thus, disrupted reconsolidation of fear conditioning can be achieved without in vivo stimulus presentation, through purely cognitive means, suggesting possible therapeutic applications. Copyright © 2016 Elsevier B.V. All rights reserved.

  14. The empirical Gaia G-band extinction coefficient

    NASA Astrophysics Data System (ADS)

    Danielski, C.; Babusiaux, C.; Ruiz-Dern, L.; Sartoretti, P.; Arenou, F.

    2018-06-01

    Context. The first Gaia data release unlocked the access to photometric information for 1.1 billion sources in the G-band. Yet, given the high level of degeneracy between extinction and spectral energy distribution for large passbands such as the Gaia G-band, a correction for the interstellar reddening is needed in order to exploit Gaia data. Aims: The purpose of this manuscript is to provide the empirical estimation of the Gaia G-band extinction coefficient kG for both the red giants and main sequence stars in order to be able to exploit the first data release DR1. Methods: We selected two samples of single stars: one for the red giants and one for the main sequence. Both samples are the result of a cross-match between Gaia DR1 and 2MASS catalogues; they consist of high-quality photometry in the G-, J- and KS-bands. These samples were complemented by temperature and metallicity information retrieved from APOGEE DR13 and LAMOST DR2 surveys, respectively. We implemented a Markov chain Monte Carlo method where we used (G - KS)0 versus Teff and (J - KS)0 versus (G - KS)0, calibration relations to estimate the extinction coefficient kG and we quantify its corresponding confidence interval via bootstrap resampling. We tested our method on samples of red giants and main sequence stars, finding consistent solutions. Results: We present here the determination of the Gaia extinction coefficient through a completely empirical method. Furthermore we provide the scientific community with a formula for measuring the extinction coefficient as a function of stellar effective temperature, the intrinsic colour (G - KS)0, and absorption.

  15. Extinct New Zealand megafauna were not in decline before human colonization

    PubMed Central

    Allentoft, Morten Erik; Heller, Rasmus; Oskam, Charlotte L.; Lorenzen, Eline D.; Hale, Marie L.; Gilbert, M. Thomas P.; Jacomb, Christopher; Holdaway, Richard N.; Bunce, Michael

    2014-01-01

    The extinction of New Zealand's moa (Aves: Dinornithiformes) followed the arrival of humans in the late 13th century and was the final event of the prehistoric Late Quaternary megafauna extinctions. Determining the state of the moa populations in the pre-extinction period is fundamental to understanding the causes of the event. We sampled 281 moa individuals and combined radiocarbon dating with ancient DNA analyses to help resolve the extinction debate and gain insights into moa biology. The samples, which were predominantly from the last 4,000 years preceding the extinction, represent four sympatric moa species excavated from five adjacent fossil deposits. We characterized the moa assemblage using mitochondrial DNA and nuclear microsatellite markers developed specifically for moa. Although genetic diversity differed significantly among the four species, we found that the millennia preceding the extinction were characterized by a remarkable degree of genetic stability in all species, with no loss of heterozygosity and no shifts in allele frequencies over time. The extinction event itself was too rapid to be manifested in the moa gene pools. Contradicting previous claims of a decline in moa before Polynesian settlement in New Zealand, our findings indicate that the populations were large and stable before suddenly disappearing. This interpretation is supported by approximate Bayesian computation analyses. Our analyses consolidate the disappearance of moa as the most rapid, human-facilitated megafauna extinction documented to date. PMID:24639531

  16. New Early Jurassic Tetrapod Assemblages Constrain Triassic-Jurassic Tetrapod Extinction Event

    NASA Astrophysics Data System (ADS)

    Olsen, P. E.; Shubin, N. H.; Anders, M. H.

    1987-08-01

    The discovery of the first definitively correlated earliest Jurassic (200 million years before present) tetrapod assemblage (Fundy basin, Newark Supergroup, Nova Scotia) allows reevaluation of the duration of the Triassic-Jurassic tetrapod extinction event. Present are tritheledont and mammal-like reptiles, prosauropod, theropod, and ornithischian dinosaurs, protosuchian and sphenosuchian crocodylomorphs, sphenodontids, and hybodont, semionotid, and palaeonisciform fishes. All of the families are known from Late Triassic and Jurassic strata from elsewhere; however, pollen and spore, radiometric, and geochemical correlation indicate an early Hettangian age for these assemblages. Because all ``typical Triassic'' forms are absent from these assemblages, most Triassic-Jurassic tetrapod extinctions occurred before this time and without the introduction of new families. As was previously suggested by studies of marine invertebrates, this pattern is consistent with a global extinction event at the Triassic-Jurassic boundary. The Manicouagan impact structure of Quebec provides dates broadly compatible with the Triassic-Jurassic boundary and, following the impact theory of mass extinctions, may be implicated in the cause.

  17. Facilitation of extinction and re-extinction of operant behavior in mice by chlordiazepoxide and D-cycloserine.

    PubMed

    Leslie, Julian C; Norwood, Kelly

    2013-05-01

    The aim was to compare operant extinction with re-extinction following re-acquisition and to investigate neuropharmacological mechanisms through administration of drugs potentiating GABAergic or glutamatergic systems. Groups of C57Bl/6 mice were trained to lever press for food on a fixed ratio schedule, then extinguished with or without pre-session chlordiazepoxide or post-session d-cycloserine administration (15mg/kg in each case), then retrained to lever press for food, then re-extinguished with or without pre-session chlordiazepoxide or post-session d-cycloserine. Under vehicle injections, extinction and re-extinction curves were indistinguishable, but drug treatments showed that there was less resistance to extinction in the re-extinction phase. Chlordiazepoxide facilitated extinction and re-extinction, with an earlier effect during re-extinction. d-Cycloserine also facilitated extinction and re-extinction, with some evidence of an earlier effect during re-extinction. These results replicate and extend earlier findings with operant extinction, but differ from some previous reports of d-cycloserine on re-extinction of Pavlovian conditioned fear. Implications for accounts of the similarities and differences between neural mechanisms of extinction following either Pavlovian or operant conditioning, and applications of these findings, are discussed. Copyright © 2013 Elsevier Inc. All rights reserved.

  18. Long-Term Maintenance of Immediate or Delayed Extinction Is Determined by the Extinction-Test Interval

    ERIC Educational Resources Information Center

    Johnson, Justin S.; Escobar, Martha; Kimble, Whitney L.

    2010-01-01

    Short acquisition-extinction intervals (immediate extinction) can lead to either more or less spontaneous recovery than long acquisition-extinction intervals (delayed extinction). Using rat subjects, we observed less spontaneous recovery following immediate than delayed extinction (Experiment 1). However, this was the case only if a relatively…

  19. Enigmatic Extinction: An Investigation of the 2175Å Extinction Bump in M101

    NASA Astrophysics Data System (ADS)

    Danowski, Meredith E.; Cook, Timothy; Gordon, Karl D.; Chakrabarti, Supriya; Lawton, Brandon L.; Misselt, Karl A.

    2014-06-01

    Evidence from studies of starburst galaxies indicates that active formation of high mass stars modifies the UV dust extinction curve as seen by a lack of the characteristic 2175Å bump. For over 45 years, the source of the 2175Å extinction feature has yet to be positively identified. Small aromatic/PAH grains are suggested as a leading contender in dust grain models. The face-on spiral galaxy M101 is an ideal laboratory for the study of dust, with many well-studied HII regions and a steep metallicity and ionization gradient.The Interstellar Medium Absorption Gradient Experiment Rocket (IMAGER) probes the correlation between dust extinction, and the metallicity and radiation environment in M101 at ultraviolet wavelengths. IMAGER simultaneously images M101 in three 400Å-wide bandpasses, measuring the apparent strength of the 2175Å bump and the UV continuum.Combining data from IMAGER with high S/N far- and near- UV observations from the MAMA detectors on the Hubble STIS instrument, we examine the apparent strength of the 2175Å bump in HII regions of M101. With additional infrared data from Spitzer, the DIRTY radiative transfer model, and stellar evolution models, we probe the correlation between the 2175Å feature and the aromatic/PAH features across HII regions of varying metallicity and radiation field hardness. The results of this experiment will directly impact our understanding of the nature of dust and our ability to accurately account for the effects of dust on observations at all redshifts.

  20. Extinction and Star Formation Study in Molecular Clouds with DENIS infrared data and USNO optical data

    NASA Astrophysics Data System (ADS)

    Cambrésy, Laurent

    1999-11-01

    This thesis consists in a study of molecular clouds, essentially of the point of view of the interstellar environment, but also of the one of the star formation. The original method to estimate extinction presented here is based on adaptive star counts as well as on a wavelet decomposition. For the first time, an extinction map of the whole sky is proposed (USNO-PMM optical data). Access to very large field maps offers the opportunity to analyze the interstellar matter distribution in various environments. A first result is that the contained mass in regions for which AV > 1 would not exceed half of the total cloud mass. Using DENIS data, it becomes possible to probe dense regions of clouds. For instance, star counts in the Chamaeleon complex show cores which were not resolved before. Moreover, the selection of stars with a strong infrared excess yields about fifty T Tauri candidates. From their luminosity function, I derived the average lifetime of circumstellar disc of low--mass stars: ~4cdot 106 years. It is difficult to understand the relation between extinction and molecular emission, but it appears clearly that molecular emission is a bad estimator of the column density for low extinction area. Actually, thresholds exist in the CO detection and I conclude that photodissociation, density and cloud geometry have important consequences on the CO emission when AV < 2. Investigation of the relation between extinction and far--infrared emission in Polaris leads to a four times larger emissivity in cold areas than in hot areas. This result explains the low temperatures in this cloud and implies severe restrictions concerning the use of far--infrared fluxes as an extinction estimator.

  1. Extinction in multiple contexts: Effects on the rate of extinction and the strength of response recovery.

    PubMed

    Bustamante, Javier; Uengoer, Metin; Thorwart, Anna; Lachnit, Harald

    2016-09-01

    In two human predictive-learning experiments, we investigated the effects of extinction in multiple contexts on the rate of extinction and the strength of response recovery. In each experiment, participants initially received acquisition training with a target cue in one context, followed by extinction either in a different context (extinction in a single context) or in three different contexts (extinction in multiple contexts). The results of both experiments showed that conducting extinction in multiple contexts led to higher levels of responding during extinction than did extinction in a single context. Additionally, Experiment 2 showed that extinction in multiple contexts prevented ABC renewal but had no detectable impact on ABA renewal. Our results are discussed within the framework of contemporary learning theories of contextual control and extinction.

  2. Extinctions. Paleontological baselines for evaluating extinction risk in the modern oceans.

    PubMed

    Finnegan, Seth; Anderson, Sean C; Harnik, Paul G; Simpson, Carl; Tittensor, Derek P; Byrnes, Jarrett E; Finkel, Zoe V; Lindberg, David R; Liow, Lee Hsiang; Lockwood, Rowan; Lotze, Heike K; McClain, Craig R; McGuire, Jenny L; O'Dea, Aaron; Pandolfi, John M

    2015-05-01

    Marine taxa are threatened by anthropogenic impacts, but knowledge of their extinction vulnerabilities is limited. The fossil record provides rich information on past extinctions that can help predict biotic responses. We show that over 23 million years, taxonomic membership and geographic range size consistently explain a large proportion of extinction risk variation in six major taxonomic groups. We assess intrinsic risk-extinction risk predicted by paleontologically calibrated models-for modern genera in these groups. Mapping the geographic distribution of these genera identifies coastal biogeographic provinces where fauna with high intrinsic risk are strongly affected by human activity or climate change. Such regions are disproportionately in the tropics, raising the possibility that these ecosystems may be particularly vulnerable to future extinctions. Intrinsic risk provides a prehuman baseline for considering current threats to marine biodiversity. Copyright © 2015, American Association for the Advancement of Science.

  3. Aerosol optical extinction during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) 2014 summertime field campaign, Colorado, USA

    NASA Astrophysics Data System (ADS)

    Dingle, Justin H.; Vu, Kennedy; Bahreini, Roya; Apel, Eric C.; Campos, Teresa L.; Flocke, Frank; Fried, Alan; Herndon, Scott; Hills, Alan J.; Hornbrook, Rebecca S.; Huey, Greg; Kaser, Lisa; Montzka, Denise D.; Nowak, John B.; Reeves, Mike; Richter, Dirk; Roscioli, Joseph R.; Shertz, Stephen; Stell, Meghan; Tanner, David; Tyndall, Geoff; Walega, James; Weibring, Petter; Weinheimer, Andrew

    2016-09-01

    Summertime aerosol optical extinction (βext) was measured in the Colorado Front Range and Denver metropolitan area as part of the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) campaign during July-August 2014. An Aerodyne cavity attenuated phase shift particle light extinction monitor (CAPS-PMex) was deployed to measure βext (at average relative humidity of 20 ± 7 %) of submicron aerosols at λ = 632 nm at 1 Hz. Data from a suite of gas-phase instrumentation were used to interpret βext behavior in various categories of air masses and sources. Extinction enhancement ratios relative to CO (Δβext / ΔCO) were higher in aged urban air masses compared to fresh air masses by ˜ 50 %. The resulting increase in Δβext / ΔCO for highly aged air masses was accompanied by formation of secondary organic aerosols (SOAs). In addition, the impacts of aerosol composition on βext in air masses under the influence of urban, natural oil and gas operations (O&G), and agriculture and livestock operations were evaluated. Estimated non-refractory mass extinction efficiency (MEE) values for different air mass types ranged from 1.51 to 2.27 m2 g-1, with the minimum and maximum values observed in urban and agriculture-influenced air masses, respectively. The mass distribution for organic, nitrate, and sulfate aerosols presented distinct profiles in different air mass types. During 11-12 August, regional influence of a biomass burning event was observed, increasing the background βext and estimated MEE values in the Front Range.

  4. Enhanced methane emission during carbonaceous sediment-basalt interactions as a mechanism for mass extinction

    NASA Astrophysics Data System (ADS)

    Kubo, A. I.; Day, J. M.; Ryabov, V. V.; Taylor, L. A.

    2016-12-01

    Precise dating techniques have established the contemporaneous eruption of the Siberian Traps at the beginning of the Permian faunal mass extinction at 248 ± 2 Ma. Within a relatively limited time-period ( 1 Ma), the Siberian Traps expelled approximately ninety percent of its total volume ( 1.5 Mkm3), each episode of volcanism adding substantial amounts of CO2, CH4, and SO2 to the atmosphere. The Permian-Triassic Boundary shows average organic carbon isotope excursions of -6.4 ± 4.4‰ (253 Ma), from a long-term average δ13Corg of -25‰. Retallack and Jahren [2008; Journal of Geology] suggested that eruption into C-rich sediments and resulting methane degassing would satisfy necessary conditions to cause such large, variable perturbations in the carbon isotope record. To test this hypothesis, we measured C isotope variations in upper crustal sediments and metalliferous basalts from the Khungtukun and Dzhatul Intrusions, of the Siberian Traps. We find that δ13C values for Siberian coal and sandstones are restricted at -23 to -25‰, with similar values measured in the metalliferous basalts. Anticipated thermogenic methane from disassociation of these sources would be considerably lighter and consistent with low δ13C isotopic values. We further test this mechanism by employing a zero dimensional energy balance model to examine three key parameters: eruption duration, amounts of CO2 and CH4 emission, and the frequency of eruptions. Greater methane emissions than previously estimated due to carbonaceous sediment-basalt interactions have a sustained temperature effect due to high global warming potential (GWP), between 28 and 36 over 100 years compared to the CO2 reference value. Our model predicts that a quick succession of massive effusive eruptions would cause a sustained and substantial temperature effect consistent with estimated equatorial levels of 40°C during the Permian-Triassic Boundary. This mechanism could explain the deficit between the amount of

  5. Metapopulation extinction risk: dispersal's duplicity.

    PubMed

    Higgins, Kevin

    2009-09-01

    Metapopulation extinction risk is the probability that all local populations are simultaneously extinct during a fixed time frame. Dispersal may reduce a metapopulation's extinction risk by raising its average per-capita growth rate. By contrast, dispersal may raise a metapopulation's extinction risk by reducing its average population density. Which effect prevails is controlled by habitat fragmentation. Dispersal in mildly fragmented habitat reduces a metapopulation's extinction risk by raising its average per-capita growth rate without causing any appreciable drop in its average population density. By contrast, dispersal in severely fragmented habitat raises a metapopulation's extinction risk because the rise in its average per-capita growth rate is more than offset by the decline in its average population density. The metapopulation model used here shows several other interesting phenomena. Dispersal in sufficiently fragmented habitat reduces a metapopulation's extinction risk to that of a constant environment. Dispersal between habitat fragments reduces a metapopulation's extinction risk insofar as local environments are asynchronous. Grouped dispersal raises the effective habitat fragmentation level. Dispersal search barriers raise metapopulation extinction risk. Nonuniform dispersal may reduce the effective fraction of suitable habitat fragments below the extinction threshold. Nonuniform dispersal may make demographic stochasticity a more potent metapopulation extinction force than environmental stochasticity.

  6. Stress before extinction learning enhances and generalizes extinction memory in a predictive learning task.

    PubMed

    Meir Drexler, Shira; Hamacher-Dang, Tanja C; Wolf, Oliver T

    2017-05-01

    In extinction learning, the individual learns that a previously acquired association (e.g. between a threat and its predictor) is no longer valid. This learning is the principle underlying many cognitive-behavioral psychotherapeutic treatments, e.g. 'exposure therapy'. However, extinction is often highly-context dependent, leading to renewal (relapse of extinguished conditioned response following context change). We have previously shown that post-extinction stress leads to a more context-dependent extinction memory in a predictive learning task. Yet as stress prior to learning can impair the integration of contextual cues, here we aim to create a more generalized extinction memory by inducing stress prior to extinction. Forty-nine men and women learned the associations between stimuli and outcomes in a predictive learning task (day 1), extinguished them shortly after an exposure to a stress/control condition (day 2), and were tested for renewal (day 3). No group differences were seen in acquisition and extinction learning, and a renewal effect was present in both groups. However, the groups differed in the strength and context-dependency of the extinction memory. Compared to the control group, the stress group showed an overall reduced recovery of responding to the extinguished stimuli, in particular in the acquisition context. These results, together with our previous findings, demonstrate that the effects of stress exposure on extinction memory depend on its timing. While post-extinction stress makes the memory more context-bound, pre-extinction stress strengthens its consolidation for the acquisition context as well, making it potentially more resistant to relapse. These results have implications for the use of glucocorticoids as extinction-enhancers in exposure therapy. Copyright © 2017 Elsevier Inc. All rights reserved.

  7. A method for identifying satiation versus extinction effects under noncontingent reinforcement schedules.

    PubMed

    Kahng, S W; Iwata, B A; Thompson, R H; Hanley, G P

    2000-01-01

    We evaluated one method for determining whether response suppression under noncontingent reinforcement (NCR) is a function of satiation or extinction. Three individuals with developmental disabilities who engaged in self-injurious behavior (SIB) or aggression participated. Results of functional analyses indicated that their problem behavior was maintained by social-positive reinforcement. NCR procedures, individualized for each participant, were implemented in a multiple baseline across subjects design and were associated with decreases in all participants' problem behavior. Identification of the mechanism by which NCR produced these effects was based on examination of cumulative records showing response patterns during and immediately following each NCR session. Satiation during NCR should lead to a temporary increase in responding during the post-NCR (extinction) period due to a transition from the availability to the unavailability of reinforcement (satiation to deprivation). Alternatively, extinction during NCR should reveal no increase in responding during the extinction period because the contingency for the problem behavior would remain unchanged and the transition from satiation to deprivation conditions would be irrelevant. Results suggested that the operative mechanisms of NCR were idiosyncratic across the 3 participants and appeared to change during treatment for 1 of the participants.

  8. Extinction and recolonization of coastal megafauna following human arrival in New Zealand

    PubMed Central

    Collins, Catherine J.; Rawlence, Nicolas J.; Prost, Stefan; Anderson, Christian N. K.; Knapp, Michael; Scofield, R. Paul; Robertson, Bruce C.; Smith, Ian; Matisoo-Smith, Elizabeth A.; Chilvers, B. Louise; Waters, Jonathan M.

    2014-01-01

    Extinctions can dramatically reshape biological communities. As a case in point, ancient mass extinction events apparently facilitated dramatic new evolutionary radiations of surviving lineages. However, scientists have yet to fully understand the consequences of more recent biological upheaval, such as the megafaunal extinctions that occurred globally over the past 50 kyr. New Zealand was the world's last large landmass to be colonized by humans, and its exceptional archaeological record documents a vast number of vertebrate extinctions in the immediate aftermath of Polynesian arrival approximately AD 1280. This recently colonized archipelago thus presents an outstanding opportunity to test for rapid biological responses to extinction. Here, we use ancient DNA (aDNA) analysis to show that extinction of an endemic sea lion lineage (Phocarctos spp.) apparently facilitated a subsequent northward range expansion of a previously subantarctic-limited lineage. This finding parallels a similar extinction–replacement event in penguins (Megadyptes spp.). In both cases, an endemic mainland clade was completely eliminated soon after human arrival, and then replaced by a genetically divergent clade from the remote subantarctic region, all within the space of a few centuries. These data suggest that ecological and demographic processes can play a role in constraining lineage distributions, even for highly dispersive species, and highlight the potential for dynamic biological responses to extinction. PMID:24827440

  9. Plants with double genomes might have had a better chance to survive the Cretaceous–Tertiary extinction event

    PubMed Central

    Fawcett, Jeffrey A.; Maere, Steven; Van de Peer, Yves

    2009-01-01

    Most flowering plants have been shown to be ancient polyploids that have undergone one or more whole genome duplications early in their evolution. Furthermore, many different plant lineages seem to have experienced an additional, more recent genome duplication. Starting from paralogous genes lying in duplicated segments or identified in large expressed sequence tag collections, we dated these youngest duplication events through penalized likelihood phylogenetic tree inference. We show that a majority of these independent genome duplications are clustered in time and seem to coincide with the Cretaceous–Tertiary (KT) boundary. The KT extinction event is the most recent mass extinction caused by one or more catastrophic events such as a massive asteroid impact and/or increased volcanic activity. These events are believed to have generated global wildfires and dust clouds that cut off sunlight during long periods of time resulting in the extinction of ≈60% of plant species, as well as a majority of animals, including dinosaurs. Recent studies suggest that polyploid species can have a higher adaptability and increased tolerance to different environmental conditions. We propose that polyploidization may have contributed to the survival and propagation of several plant lineages during or following the KT extinction event. Due to advantages such as altered gene expression leading to hybrid vigor and an increased set of genes and alleles available for selection, polyploid plants might have been better able to adapt to the drastically changed environment 65 million years ago. PMID:19325131

  10. Temporal factors in the extinction of fear in inbred mouse strains differing in extinction efficacy

    PubMed Central

    2013-01-01

    Background Various neuropsychiatric conditions, including posttraumatic stress disorder (PTSD), are characterized by deficient fear extinction, but individuals differ greatly in risk for these. While there is growing evidence that fear extinction is influenced by certain procedural variables, it is unclear how these influences might vary across individuals and subpopulations. To model individual differences in fear extinction, prior studies identified a strain of inbred mouse, 129S1/SvImJ (S1), which exhibits a profound deficit in fear extinction, as compared to other inbred strains, such as C57BL/6J (B6). Methods Here, we assessed the effects of procedural variables on the impaired extinction phenotype of the S1 strain and, by comparison, the extinction-intact B6 strain. The variables studied were 1) the interval between conditioning and extinction, 2) the interval between cues during extinction training, 3) single-cue exposure before extinction training, and 4) extinction of a second-order conditioned cue. Results Conducting extinction training soon after (‘immediately’) conditioning attenuated fear retrieval in S1 mice and impaired extinction in B6 mice. Spacing cue presentations with long inter-trial intervals during extinction training augmented fear in S1 and B6 mice. The effect of spacing was lost with one-trial fear conditioning in B6, but not S1 mice. A single exposure to a conditioned cue before extinction training did not alter extinction retrieval, either in B6 or S1 mice. Both the S1 and B6 strains exhibited robust second-order fear conditioning, in which a cue associated with footshock was sufficient to serve as a conditioned exciter to condition a fear association to a second cue. B6 mice extinguished the fear response to the second-order conditioned cue, but S1 mice failed to do so. Conclusions These data provide further evidence that fear extinction is strongly influenced by multiple procedural variables and is so in a highly strain

  11. Temporal factors in the extinction of fear in inbred mouse strains differing in extinction efficacy.

    PubMed

    MacPherson, Kathryn; Whittle, Nigel; Camp, Marguerite; Gunduz-Cinar, Ozge; Singewald, Nicolas; Holmes, Andrew

    2013-07-05

    Various neuropsychiatric conditions, including posttraumatic stress disorder (PTSD), are characterized by deficient fear extinction, but individuals differ greatly in risk for these. While there is growing evidence that fear extinction is influenced by certain procedural variables, it is unclear how these influences might vary across individuals and subpopulations. To model individual differences in fear extinction, prior studies identified a strain of inbred mouse, 129S1/SvImJ (S1), which exhibits a profound deficit in fear extinction, as compared to other inbred strains, such as C57BL/6J (B6). Here, we assessed the effects of procedural variables on the impaired extinction phenotype of the S1 strain and, by comparison, the extinction-intact B6 strain. The variables studied were 1) the interval between conditioning and extinction, 2) the interval between cues during extinction training, 3) single-cue exposure before extinction training, and 4) extinction of a second-order conditioned cue. Conducting extinction training soon after ('immediately') conditioning attenuated fear retrieval in S1 mice and impaired extinction in B6 mice. Spacing cue presentations with long inter-trial intervals during extinction training augmented fear in S1 and B6 mice. The effect of spacing was lost with one-trial fear conditioning in B6, but not S1 mice. A single exposure to a conditioned cue before extinction training did not alter extinction retrieval, either in B6 or S1 mice. Both the S1 and B6 strains exhibited robust second-order fear conditioning, in which a cue associated with footshock was sufficient to serve as a conditioned exciter to condition a fear association to a second cue. B6 mice extinguished the fear response to the second-order conditioned cue, but S1 mice failed to do so. These data provide further evidence that fear extinction is strongly influenced by multiple procedural variables and is so in a highly strain-dependent manner. This suggests that the efficacy of

  12. Spontaneous Recovery After Extinction of the Conditioned Proboscis Extension Response in the Honeybee

    PubMed Central

    Sandoz, Jean-Christophe; Pham-Delègue, Minh-Hà

    2004-01-01

    In honeybees, the proboscis extension response (PER) can be conditioned by associating an odor stimulus (CS) to a sucrose reward (US). Conditioned responses to the CS, which are acquired by most bees after a single CS-US pairing, disappear after repeated unrewarded presentations of the CS, a process called extinction. Extinction is usually thought to be based either on (1) the disruption of the stored CS-US association, or (2) the formation of an inhibitory “CS-no US” association that is better retrieved than the initial CS-US association. The observation of spontaneous recovery, i.e., the reappearance of responses to the CS after time passes following extinction, is traditionally interpreted as a proof for the formation of a transient inhibitory association. To provide a better understanding of extinction in honeybees, we examined whether time intervals during training and extinction or the number of conditioning and extinction trials have an effect on the occurrence of spontaneous recovery. We found that spontaneous recovery mostly occurs when conditioning and testing took place in a massed fashion (1-min intertrial intervals). Moreover, spontaneous recovery depended on the time elapsed since extinction, 1 h being an optimum. Increasing the number of conditioning trials improved the spontaneous recovery level, whereas increasing the number of extinction trials reduced it. Lastly, we show that after single-trial conditioning, spontaneous recovery appears only once after extinction. These elements suggest that in honeybees extinction of the PER actually reflects the impairment of the CS-US association, but that depending on training parameters different memory substrates are affected. PMID:15466313

  13. Severest crisis overlooked—Worst disruption of terrestrial environments postdates the Permian–Triassic mass extinction

    PubMed Central

    Hochuli, Peter A.; Sanson-Barrera, Anna; Schneebeli-Hermann, Elke; Bucher, Hugo

    2016-01-01

    Generally Early Triassic floras are believed to be depauperate, suffering from protracted recovery following the Permian–Triassic extinction event. Here we present palynological data of an expanded East Greenland section documenting recovered floras in the basal Triassic (Griesbachian) and a subsequent fundamental floral turnover, postdating the Permian–Triassic boundary extinction by about 500 kyrs. This event is marked by a swap in dominating floral elements, changing from gymnosperm pollen-dominated associations in the Griesbachian to lycopsid spore-dominated assemblages in the Dienerian. This turnover coincides with an extreme δ13Corg negative shift revealing a severe environmental crisis, probably induced by volcanic outbursts of the Siberian Traps, accompanied by a climatic turnover, changing from cool and dry in the Griesbachian to hot and humid in the Dienerian. Estimates of sedimentation rates suggest that this environmental alteration took place within some 1000 years. Similar, coeval changes documented on the North Indian Margin (Pakistan) and the Bowen Basin (Australia) indicate the global extent of this crisis. Our results evidence the first profound disruption of the recovery of terrestrial environments about 500kyrs after the Permian–Triassic extinction event. It was followed by another crisis, about 1myrs later thus, the Early Triassic can be characterised as a time of successive environmental crises. PMID:27340926

  14. Uncertain sightings and the extinction of the Ivory-billed Woodpecker.

    PubMed

    Solow, Andrew; Smith, Woollcott; Burgman, Mark; Rout, Tracy; Wintle, Brendan; Roberts, David

    2012-02-01

    The extinction of a species can be inferred from a record of its sightings. Existing methods for doing so assume that all sightings in the record are valid. Often, however, there are sightings of uncertain validity. To date, uncertain sightings have been treated in an ad hoc way, either excluding them from the record or including them as if they were certain. We developed a Bayesian method that formally accounts for such uncertain sightings. The method assumes that valid and invalid sightings follow independent Poisson processes and use noninformative prior distributions for the rate of valid sightings and for a measure of the quality of uncertain sightings. We applied the method to a recently published record of sightings of the Ivory-billed Woodpecker (Campephilus principalis). This record covers the period 1897-2010 and contains 39 sightings classified as certain and 29 classified as uncertain. The Bayes factor in favor of extinction was 4.03, which constitutes substantial support for extinction. The posterior distribution of the time of extinction has 3 main modes in 1944, 1952, and 1988. The method can be applied to sighting records of other purportedly extinct species. ©2011 Society for Conservation Biology.

  15. Chronic cannabis use is associated with impaired fear extinction in humans.

    PubMed

    Papini, Santiago; Ruglass, Lesia M; Lopez-Castro, Teresa; Powers, Mark B; Smits, Jasper A J; Hien, Denise A

    2017-01-01

    The use of fear conditioning and extinction paradigms to examine intermediate phenotypes of anxiety and stress-related disorders has facilitated the identification of neurobiological mechanisms that underlie specific components of abnormal psychological functioning. Across species, acute pharmacologic manipulation of the endogenous cannabinoid system has provided evidence of its critical role in fear extinction, but the effects of chronic cannabis on extinction are relatively understudied. In rats, chronic cannabinoid administration impairs fear extinction in a drug-free state. Here we examine whether chronic cannabis use is associated with impaired fear extinction in humans. Participants were healthy chronic cannabis users (n = 20) and nonuser controls with minimal lifetime cannabis use (n = 20) matched on age, sex, and race who all screened negative for psychiatric disorders. A 2-day differential fear conditioning paradigm was used to test the hypothesis that chronic cannabis use would be associated with impaired extinction of the skin conductance response. Consistent with hypotheses, chronic cannabis use was associated with reduced within-session extinction of skin conductance response on Day 1 (d = 0.78), and between-session extinction on Day 2 (d = 0.76). Unexpectedly, cannabis use was also associated with reduced subjective differentiation between threat and safety stimuli during conditioning. Replication and translation of findings are necessary to test potential mechanisms directly and examine whether impairments can be reversed pharmacologically or after a period of cannabis abstinence. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

  16. Microconchids from microbialite ecosystem immediately after end-Permian mass extinction: ecologic selectivity and implications for microbialite ecosystem structure

    NASA Astrophysics Data System (ADS)

    Yang, H.; Chen, Z.; Wang, Y. B.; Ou, W.; Liao, W.; Mei, X.

    2013-12-01

    The Permian-Triassic (P-Tr) carbonate successions are often characterized by the presence of microbialite buildups worldwide. The widespread microbialites are believed as indication of microbial proliferation immediately after the P-Tr mass extinction. The death of animals representing the primary consumer trophic structure of marine ecosystem in the P-Tr crisis allows the bloom of microbes as an important primary producer in marine trophic food web structure. Thus, the PTB microbialite builders have been regarded as disaster taxa of the P-Tr ecologic crisis. Microbialite ecosystems were suitable for most organisms to inhabit. However, increasing evidence show that microbialite dwellers are also considerably abundant and diverse, including mainly foraminifers Earlandia sp. and Rectocornuspira sp., lingulid brachiopods, ostrocods, gastropods, and microconchids. In particular, ostracods are extremely abundant in this special ecosystem. Microconchid-like calcareous tubes are also considerably abundant. Here, we have sampled systematically a PTB microbialite deposit from the Dajiang section, southern Guizhou Province, southwest China and have extracted abundant isolated specimens of calcareous worm tubes. Quantitative analysis enables to investigate stratigraphic and facies preferences of microconchids in the PTB microbialites. Our preliminary result indicates that three microconchid species Microconchus sp., Helicoconchus elongates and Microconchus aberrans inhabited in microbialite ecosystem. Most microconchilds occurred in the upper part of the microbialite buildup and the grainstone-packstone microfacies. Very few microconchilds were found in the rocks bearing well-developed microbialite structures. Their stratigraphic and environmental preferences indicate proliferation of those metazoan organisms is coupled with ebb of the microbialite development. They also proliferated in some local niches in which microbial activities were not very active even if those

  17. Timing of global regression and microbial bloom linked with the Permian-Triassic boundary mass extinction: implications for driving mechanisms

    PubMed Central

    Baresel, Björn; Bucher, Hugo; Bagherpour, Borhan; Brosse, Morgane; Guodun, Kuang; Schaltegger, Urs

    2017-01-01

    New high-resolution U-Pb dates indicate a duration of 89 ± 38 kyr for the Permian hiatus and of 14 ± 57 kyr for the overlying Triassic microbial limestone in shallow water settings of the Nanpanjiang Basin, South China. The age and duration of the hiatus coincides with the Permian-Triassic boundary (PTB) and the extinction interval in the Meishan Global Stratotype Section and Point, and strongly supports a glacio-eustatic regression, which best explains the genesis of the worldwide hiatus straddling the PTB in shallow water records. In adjacent deep marine troughs, rates of sediment accumulation display a six-fold decrease across the PTB compatible with a dryer and cooler climate as indicated by terrestrial plants. Our model of the Permian-Triassic boundary mass extinction (PTBME) hinges on the synchronicity of the hiatus with the onset of the Siberian Traps volcanism. This early eruptive phase released sulfur-rich volatiles into the stratosphere, thus simultaneously eliciting a short-lived ice age responsible for the global regression and a brief but intense acidification. Abrupt cooling, shrunk habitats on shelves and acidification may all have synergistically triggered the PTBME. Subsequently, the build-up of volcanic CO2 induced a transient cool climate whose early phase saw the deposition of the microbial limestone. PMID:28262815

  18. Timing of global regression and microbial bloom linked with the Permian-Triassic boundary mass extinction: implications for driving mechanisms

    NASA Astrophysics Data System (ADS)

    Baresel, Björn; Bucher, Hugo; Bagherpour, Borhan; Brosse, Morgane; Guodun, Kuang; Schaltegger, Urs

    2017-03-01

    New high-resolution U-Pb dates indicate a duration of 89 ± 38 kyr for the Permian hiatus and of 14 ± 57 kyr for the overlying Triassic microbial limestone in shallow water settings of the Nanpanjiang Basin, South China. The age and duration of the hiatus coincides with the Permian-Triassic boundary (PTB) and the extinction interval in the Meishan Global Stratotype Section and Point, and strongly supports a glacio-eustatic regression, which best explains the genesis of the worldwide hiatus straddling the PTB in shallow water records. In adjacent deep marine troughs, rates of sediment accumulation display a six-fold decrease across the PTB compatible with a dryer and cooler climate as indicated by terrestrial plants. Our model of the Permian-Triassic boundary mass extinction (PTBME) hinges on the synchronicity of the hiatus with the onset of the Siberian Traps volcanism. This early eruptive phase released sulfur-rich volatiles into the stratosphere, thus simultaneously eliciting a short-lived ice age responsible for the global regression and a brief but intense acidification. Abrupt cooling, shrunk habitats on shelves and acidification may all have synergistically triggered the PTBME. Subsequently, the build-up of volcanic CO2 induced a transient cool climate whose early phase saw the deposition of the microbial limestone.

  19. Is extinction age dependent?

    USGS Publications Warehouse

    Doran, N.A.; Arnold, A.J.; Parker, W.C.; Huffer, F.W.

    2006-01-01

    Age-dependent extinction is an observation with important biological implications. Van Valen's Red Queen hypothesis triggered three decades of research testing its primary implication: that age is independent of extinction. In contrast to this, later studies with species-level data have indicated the possible presence of age dependence. Since the formulation of the Red Queen hypothesis, more powerful tests of survivorship models have been developed. This is the first report of the application of the Cox Proportional Hazards model to paleontological data. Planktonic foraminiferal morphospecies allow the taxonomic and precise stratigraphic resolution necessary for the Cox model. As a whole, planktonic foraminiferal morphospecies clearly show age-dependent extinction. In particular, the effect is attributable to the presence of shorter-ranged species (range < 4 myr) following extinction events. These shorter-ranged species also possess tests with unique morphological architecture. The morphological differences are probably epiphenomena of underlying developmental and heterochronic processes of shorter-ranged species that survived various extinction events. Extinction survivors carry developmental and morphological characteristics into postextinction recovery times, and this sets them apart from species populations established independently of extinction events. Copyright ?? 2006, SEPM (Society for Sedimentary Geology).

  20. δ 13C evidence that high primary productivity delayed recovery from end-Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Meyer, K. M.; Yu, M.; Jost, A. B.; Kelley, B. M.; Payne, J. L.

    2011-02-01

    Euxinia was widespread during and after the end-Permian mass extinction and is commonly cited as an explanation for delayed biotic recovery during Early Triassic time. This anoxic, sulfidic episode has been ascribed to both low- and high-productivity states in the marine water column, leaving the causes of euxinia and the mechanisms underlying delayed recovery poorly understood. Here we use isotopic analysis to examine the changing chemical structure of the water column through the recovery interval and thereby better constrain paleoproductivity. The δ 13C of limestones from 5 stratigraphic sections in south China displays a negative gradient of approximately 4‰ from shallow-to-deep water facies within the Lower Triassic. This intense gradient declines within Spathian and lowermost Middle Triassic strata, coincident with accelerated biotic recovery and carbon cycle stabilization. Model simulations show that high nutrient levels and a vigorous biological pump are required to sustain such a large gradient in δ 13C, indicating that Early Triassic ocean anoxia and delayed recovery of benthic animal ecosystems resulted from too much productivity rather than too little.

  1. PULSATION-TRIGGERED MASS LOSS FROM AGB STARS: THE 60 DAY CRITICAL PERIOD

    SciTech Connect

    McDonald, I.; Zijlstra, A. A., E-mail: iain.mcdonald-2@jb.man.ac.uk, E-mail: albert.zijlstra@manchester.ac.uk

    2016-06-01

    Low- and intermediate-mass stars eject much of their mass during the late, red giant branch (RGB) phase of evolution. The physics of their strong stellar winds is still poorly understood. In the standard model, stellar pulsations extend the atmosphere, allowing a wind to be driven through radiation pressure on condensing dust particles. Here, we investigate the onset of the wind, using nearby RGB stars drawn from the Hipparcos catalog. We find a sharp onset of dust production when the star first reaches a pulsation period of 60 days. This approximately coincides with the point where the star transitions to themore » first overtone pulsation mode. Models of the spectral energy distributions show stellar mass-loss rate suddenly increasing at this point, by a factor of ∼10 over the existing (chromospherically driven) wind. The dust emission is strongly correlated with both pulsation period and amplitude, indicating stellar pulsation is the main trigger for the strong mass loss, and determines the mass-loss rate. Dust emission does not strongly correlate with stellar luminosity, indicating radiation pressure on dust has little effect on the mass-loss rate. RGB stars do not normally appear to produce dust, whereas dust production by asymptotic giant branch stars appears commonplace, and is probably ubiquitous above the RGB-tip luminosity. We conclude that the strong wind begins with a step change in mass-loss rate and is triggered by stellar pulsations. A second rapid mass-loss-rate enhancement is suggested when the star transitions to the fundamental pulsation mode at a period of ∼300 days.« less

  2. Forming competing fear learning and extinction memories in adolescence makes fear difficult to inhibit

    PubMed Central

    Richardson, Rick

    2015-01-01

    Fear inhibition is markedly impaired in adolescent rodents and humans. The present experiments investigated whether this impairment is critically determined by the animal's age at the time of fear learning or their age at fear extinction. Male rats (n = 170) were tested for extinction retention after conditioning and extinction at different ages. We examined neural correlates of impaired extinction retention by detection of phosphorylated mitogen-activated protein kinase immunoreactivity (pMAPK-IR) in several brain regions. Unexpectedly, adolescent rats exhibited good extinction retention if fear was acquired before adolescence. Further, fear acquired in adolescence could be successfully extinguished in adulthood but not within adolescence. Adolescent rats did not show extinction-induced increases in pMAPK-IR in the medial prefrontal cortex or the basolateral amygdala, or a pattern of reduced caudal central amygdala pMAPK-IR, as was observed in juveniles. This dampened prefrontal and basolateral amygdala MAPK activation following extinction in adolescence occurred even when there was no impairment in extinction retention. In contrast, only adolescent animals that exhibited impaired extinction retention showed elevated pMAPK-IR in the posterior paraventricular thalamus. These data suggest that neither the animal's age at the time of fear acquisition or extinction determines whether impaired extinction retention is exhibited. Rather, it appears that forming competing fear conditioning and extinction memories in adolescence renders this a vulnerable developmental period in which fear is difficult to inhibit. Furthermore, even under conditions that promote good extinction, the neural correlates of extinction in adolescence are different than those recruited in animals of other ages. PMID:26472643

  3. Variability in life-history and ecological traits is a buffer against extinction in mammals.

    PubMed

    González-Suárez, Manuela; Revilla, Eloy

    2013-02-01

    Anthropogenic degradation of the world's ecosystems is leading to a widespread and accelerating loss of biodiversity. However, not all species respond equally to existing threats, raising the question: what makes a species more vulnerable to extinction? We propose that higher intraspecific variability may reduce the risk of extinction, as different individuals and populations within a species may respond differently to occurring threats. Supporting this prediction, our results show that mammalian species with more variable adult body masses, litter sizes, sexual maturity ages and population densities are less vulnerable to extinction. Our findings reveal the role of local variation among populations, particularly of large mammals, as a buffering mechanism against extinction, and emphasise the importance of considering trait variation in comparative analyses and conservation management. © 2012 Blackwell Publishing Ltd/CNRS.

  4. On Kill Curves and Sampling Protocols: Studying the Relationships between Impact and Extinction

    NASA Astrophysics Data System (ADS)

    Ward, Peter D.

    1997-05-01

    The pioneering efforts of Raup (1990) have suggested that a relationship exists between crater diameter and percentage of organisms killed as a result of meteor or comet impact with the Earth. The new data (coming from study of the Manson and Chicxulub craters) suggest that the nature of target rock may be a factor nearly as important as impacter size, and that other aspects of the target, including its latitude, the atmospheric and climate conditions characterizing the Earth, as well as the stage of biological evolution and community development at the time of impact are factors which all must be factored into any new kill curve. It may be that no single 'curve' is appropriate, but that a family of curves may be necessary to model the biological effects of large impacts. We propose that a new protocol be developed to better constrain and understand the relationship between impact and extinction. Rather than searching known mass extinction boundaries for evidence of impact (an exercise which up to now has demonstrated that only the Chicxulub crater can be unambiguously related to a mass extinction of planetary scale), we propose that four known craters be investigated to see if they are temporally correlated with extinction at any detectable level. We suggest that Kara, Popigai, Manson, and Manicouagan Craters be investigated in the following way. First, what is their age? The Manson lesson is that the first step in understanding the relationship between impact and extinction is through reliable age dating. Second, can distal components of the impact ejecta (spherules, shocked quartz, and mineral signatures) be located from sedimentary record? Third, once identified, do these signatures coincide with paleontological or geochemical markers of extinction in either the synoptic literature, or from actual outcrops (or deep sea cores).

  5. Rats that sign-track are resistant to Pavlovian but not instrumental extinction

    PubMed Central

    Ahrens, Allison M.; Singer, Bryan F.; Fitzpatrick, Christopher J.; Morrow, Jonathan D.; Robinson, Terry E.

    2015-01-01

    Individuals vary in the extent to which they attribute incentive salience to a discrete cue (conditioned stimulus; CS) that predicts reward delivery (unconditioned stimulus; US), which results in some individuals approaching and interacting with the CS (sign-trackers; STs) more than others (goal-trackers; GTs). Here we asked how periods of non-reinforcement influence conditioned responding in STs vs. GTs, in both Pavlovian and instrumental tasks. After classifying rats as STs or GTs by pairing a retractable lever (the CS) with the delivery of a food pellet (US), we introduced periods of non-reinforcement, first by simply withholding the US (i.e., extinction training; experiment 1), then by signaling alternating periods of reward (R) and non-reward (NR) within the same session (experiments 2 and 3). We also examined how alternating R and NR periods influenced instrumental responding for food (experiment 4). STs and GTs did not differ in their ability to discriminate between R and NR periods in the instrumental task. However, in Pavlovian settings STs and GTs responded to periods of non-reward very differently. Relative to STs, GTs very rapidly modified their behavior in response to periods of non-reward, showing much faster extinction and better and faster discrimination between R and NR conditions. These results highlight differences between Pavlovian and instrumental extinction learning, and suggest that if a Pavlovian CS is strongly attributed with incentive salience, as in STs, it may continue to bias attention toward it, and to facilitate persistent and relatively inflexible responding, even when it is no longer followed by reward. PMID:26235331

  6. The impact of the Cretaceous-Paleogene (K-Pg) mass extinction event on the global sulfur cycle: Evidence from Seymour Island, Antarctica

    NASA Astrophysics Data System (ADS)

    Witts, James D.; Newton, Robert J.; Mills, Benjamin J. W.; Wignall, Paul B.; Bottrell, Simon H.; Hall, Joanna L. O.; Francis, Jane E.; Alistair Crame, J.

    2018-06-01

    The Cretaceous-Paleogene (K-Pg) mass extinction event 66 million years ago led to large changes to the global carbon cycle, primarily via a decrease in primary or export productivity of the oceans. However, the effects of this event and longer-term environmental changes during the Late Cretaceous on the global sulfur cycle are not well understood. We report new carbonate associated sulfate (CAS) sulfur isotope data derived from marine macrofossil shell material from a highly expanded high latitude Maastrichtian to Danian (69-65.5 Ma) succession located on Seymour Island, Antarctica. These data represent the highest resolution seawater sulfate record ever generated for this time interval, and are broadly in agreement with previous low-resolution estimates for the latest Cretaceous and Paleocene. A vigorous assessment of CAS preservation using sulfate oxygen, carbonate carbon and oxygen isotopes and trace element data, suggests factors affecting preservation of primary seawater CAS isotopes in ancient biogenic samples are complex, and not necessarily linked to the preservation of original carbonate mineralogy or chemistry. Primary data indicate a generally stable sulfur cycle in the early-mid Maastrichtian (69 Ma), with some fluctuations that could be related to increased pyrite burial during the 'mid-Maastrichtian Event'. This is followed by an enigmatic +4‰ increase in δ34SCAS during the late Maastrichtian (68-66 Ma), culminating in a peak in values in the immediate aftermath of the K-Pg extinction which may be related to temporary development of oceanic anoxia in the aftermath of the Chicxulub bolide impact. There is no evidence of the direct influence of Deccan volcanism on the seawater sulfate isotopic record during the late Maastrichtian, nor of a direct influence by the Chicxulub impact itself. During the early Paleocene (magnetochron C29R) a prominent negative excursion in seawater δ34S of 3-4‰ suggests that a global decline in organic carbon burial

  7. Extinction of Cocaine Seeking Requires a Window of Infralimbic Pyramidal Neuron Activity after Unreinforced Lever Presses

    PubMed Central

    Nett, Kelle E.; Cosme, Caitlin V.; Worth, Wensday R.; Wemmie, John A.

    2017-01-01

    The infralimbic cortex (IL) mediates extinction learning and the active suppression of cocaine-seeking behavior. However, the precise temporal relationship among IL activity, lever pressing, and extinction learning is unclear. To address this issue, we used activity-guided optogenetics in male Sprague Dawley rats to silence IL pyramidal neurons optically for 20 s immediately after unreinforced lever presses during early extinction training after cocaine self-administration. Optical inhibition of the IL increased active lever pressing during shortened extinction sessions, but did not alter the retention of the extinction learning as assessed in ensuing extinction sessions with no optical inhibition. During subsequent cued reinstatement sessions, rats that had previously received optical inhibition during the extinction sessions showed increased cocaine-seeking behavior. These findings appeared to be specific to inhibition during the post-lever press period because IL inhibition given in a noncontingent, pseudorandom manner during extinction sessions did not produce the same effects. Illumination alone (i.e., with no opsin expression) and food-seeking control experiments also failed to produce the same effects. In another experiment, IL inhibition after lever presses during cued reinstatement sessions increased cocaine seeking during those sessions. Finally, inhibition of the prelimbic cortex immediately after unreinforced lever presses during shortened extinction sessions decreased lever pressing during these sessions, but had no effect on subsequent reinstatement. These results indicate that IL activity immediately after unreinforced lever presses is necessary for normal extinction of cocaine seeking, suggesting that critical encoding of the new contingencies between a lever press and a cocaine reward occurs during that period. SIGNIFICANCE STATEMENT The infralimbic cortex (IL) contributes to the extinction of cocaine-seeking behavior, but the precise relationship

  8. The Late Ordovician Extinction: How it became the best understood of the five major extinctions.

    NASA Astrophysics Data System (ADS)

    Sheehan, P.

    2003-04-01

    The end Ordovician extinction has become arguably the best-understood major extinction event in Earth History. A plethora of workers have established the pattern of faunal change and causes of the extinction with remarkably little disagreement. The first indication of increased extinction at the end of the Ordovician was a graph of global diversity patterns by Norman Newell in 1967, although he did not recognize it as a major event. The presence of a major extinction event became clear as William Berry and Art Boucot assembled data for Silurian correlation charts in the late 1960s. The first reports of North African glaciation in the late 1960s provided a cause for the extinction and study of the event snowballed. It was no accident that recognition of the extinction began in North America, because it was there that the extinction completely overturned faunas in the epicontinental seas. Glacio-eustatic regression of shallow seaway coincided with the disappearance of endemic Laurentian faunas and replacement by a highly cosmopolitan fauna in the Silurian. Once the event was established in North America, paleontologists soon found evidence of the event around the globe. The well-documented Hirnantia Fauna was found to correspond to the glacial interval, and Pat Brenchley soon recognized that there were two pulses of extinction, at the beginning and end of the glaciation. At the same time that the faunal changes were being documented geologic studies of the glaciation provided information on the environmental changes associated with the extinction. The timing of the glacial maximum was established in Africa and by the presence of dropstones in high latitude marine rocks. The 1990s saw geochemical techniques employed that allowed examination of atmospheric CO2 and temperature changes. In many places carbonate deposition declined. Glacio-eustatic regression was obvious in many areas, and a sea-level decline in the range of 50-100 m was established. Shallow

  9. Tying Extinction Events to Comet Impacts Large Enough to Cause an Extinction in Themselves.

    NASA Astrophysics Data System (ADS)

    Burgener, J. A.

    2017-12-01

    Comets over 35 km in size impacting Earth will create vast fireballs, and will boil large parts of the oceans, causing extinction events in themselves. They will likely provide enough energy to shatter the crust and eject large masses of molten rock from the mantle, forming traps. Traps are clearly associated with extinction events, but are not expected to cause extinctions. While Chicxulub is recognized to have occurred at the time of the K/Pg boundary layer, it is recognized as being too small in itself to cause an extinction. Are large comet impacts likely? The Kuiper belt has more than 100,000 objects over 100 km in diameter and millions over 10 km. Typically their orbits are less stable than asteroid orbits due to large bodies such as Pluto moving through the belt. The asteroid belt has only 10,000 objects over 10 km diameter. Comet impacts should be more common than asteroid impacts, yet none of the recognized craters are expected to be due to comets. There are many features on Earth that are poorly explained by Plate Tectonics that would be well explained if they were considered to be comet impact craters. A consideration of the Black Sea and the Tarim Basin will show that impact interpretations are a better fit than the present Plate Tectonics' explanations. Both basins are in the midst of mountain building from plate collisions, but are themselves not being disturbed by the plate collisions. Both are ellipses angled at 23.4 degrees to the equator, matching the angle expected for a low angle impact from a comet traveling in the ecliptic. Both are too deep at 15 km depths to be standard oceans (typically 5 km deep). Both are filled with horizontal layers of sediments, undisturbed by the mountain building occurring at the edges. Both have thin crusts and high Moho boundaries. Both have thin lithosphere. Yet both show GPS movement of the land around them moving away from them, as though they were much thicker and stronger than the surrounding land. The Tarim

  10. Endocranial Morphology of the Extinct North American Lion (Panthera atrox).

    PubMed

    Cuff, Andrew R; Stockey, Christopher; Goswami, Anjali

    2016-01-01

    The extinct North American lion (Panthera atrox) is one of the largest felids (Mammalia, Carnivora) to have ever lived, and it is known from a plethora of incredibly well-preserved remains. Despite this abundance of material, there has been little research into its endocranial anatomy. CT scans of a skull of P. atrox from the Pleistocene La Brea Tar pits were used to generate the first virtual endocranium for this species and to elucidate previously unknown details of its brain size and gross structure, cranial nerves, and inner-ear morphology. Results show that its gross brain anatomy is broadly similar to that of other pantherines, although P. atrox displays less cephalic flexure than either extant lions or tigers, instead showing a brain shape that is reminiscent of earlier felids. Despite this unusual reduction in flexure, the estimated absolute brain size for this specimen is one of the largest reported for any felid, living or extinct. Its encephalization quotient (brain size as a fraction of the expected brain mass for a given body mass) is also larger than that of extant lions but similar to that of the other pantherines. The advent of CT scans has allowed nondestructive sampling of anatomy that cannot otherwise be studied in these extinct lions, leading to a more accurate reconstruction of endocranial morphology and its evolution. © 2017 S. Karger AG, Basel.

  11. Biological hierarchies and the nature of extinction.

    PubMed

    Congreve, Curtis R; Falk, Amanda R; Lamsdell, James C

    2018-05-01

    could be used to suggest that environmentally mediated patterns of extinction or slowed speciation across geological time are largely artefacts of poor preservation or a coarse temporal scale. We demonstrate how MALF fits into a hierarchical framework, showing that MALF can be a primary forcing mechanism at lower scales that still results in differential survivorship patterns at the species and clade level which vary depending upon the initial environmental forcing mechanism. Thus, even if MALF is the primary mechanism of extinction across all mass extinction events, the primary environmental cause of these events will still affect the system and result in differential responses. Therefore, patterns at both temporal scales are relevant. © 2017 Cambridge Philosophical Society.

  12. Gradients of Fear Potentiated Startle During Generalization, Extinction, and Extinction Recall--and Their Relations With Worry.

    PubMed

    Dunning, Jonathan P; Hajcak, Greg

    2015-09-01

    It is well established that fear conditioning plays a role in the development and maintenance of anxiety disorders. Moreover, abnormalities in fear generalization, extinction, and extinction recall have also been associated with anxiety. The present study used a generalization paradigm to examine fear processing during phases of generalization, extinction, and extinction recall. Specifically, participants were shocked following a CS+ and were also presented with stimuli that ranged in perceptual similarity to the CS+ (i.e., 20%, 40%, or 60% smaller or larger than the CS+) during a fear generalization phase. Participants were also presented with the same stimuli during an extinction phase and an extinction recall phase 1week later; no shocks were presented during extinction or recall. Lastly, participants completed self-report measures of worry and trait anxiety. Results indicated that fear potentiated startle (FPS) to the CS+ and GS±20% shapes was present in generalization and extinction, suggesting that fear generalization persisted into extinction. FPS to the CS+ was also evident 1 week later during extinction recall. Higher levels of worry were associated with greater FPS to the CS+ during generalization and extinction phases. Moreover, individuals high in worry had fear response gradients that were steeper during both generalization and extinction. This suggests that high levels of worry are associated with greater discriminative fear conditioning to threatening compared to safe stimuli and less fear generalization to perceptually similar stimuli. Copyright © 2015. Published by Elsevier Ltd.

  13. Constraining the time of extinction of the South American fox Dusicyon avus (Carnivora, Canidae) during the late Holocene.

    NASA Astrophysics Data System (ADS)

    Prevosti, Francisco; Santiago, Fernando; Prates, Luciano; Salemme, Mónica; Martin, Fabiana

    2010-05-01

    The mass extinction at the end of the Pleistocene affected South America during the Late Pleistocene and the Early Holocene, when megamammals and large mammals disappeared. Several carnivores became extinct, like the sabretooth Smilodon, the short face bear (Arctotherium) and some large canids (i.e. Protocyon, Canis dirus). After this mass event virtually no carnivores became extinct in South America. The only exception is the fox Dusicyon avus, a middle sized canid (estimated body mass between 10-15 kg) with a more carnivore diet than the living South American foxes (i.e. Lycalopex culpaeus). The last record of the species comes from middle-late Holocene archaeological sites in the Pampean Region (Argentina) and Patagonia (Argentina and Chile). During the Late Pleistocene D. avus had a wide distribution, that covered part of Uruguay, Argentina (Buenos Aires province) and the southernmost Chile. Albeit some remains from late Holocene sites have been published, these remains lack of isotopic dates that could (allow?) constraint (to determine) the date of extinction of this fox. In this contribution we present several new records from the Pampean Region and Patagonia, and several taxon dates. The new records indicate that D. avus disappeared in the late Holocene at least ≈ 3000 years BP in the island of Tierra del Fuego (Patagonia) and ≈ 1600 BP in the continent. Since at this time humans were occupying most of the Pampas and Patagonia a revision of the causes behind the extinction of this fox is required.

  14. Duration of extinction trials as a determinant of instrumental extinction in terrestrial toads (Rhinella arenarum).

    PubMed

    Puddington, Martín M; Papini, Mauricio R; Muzio, Rubén N

    2018-01-01

    Instrumental learning guides behavior toward resources. When such resources are no longer available, approach to previously reinforced locations is reduced, a process called extinction. The present experiments are concerned with factors affecting the extinction of acquired behaviors in toads. In previous experiments, total reward magnitude in acquisition and duration of extinction trials were confounded. The present experiments were designed to test the effects of these factors in factorial designs. Experiment 1 varied reward magnitude (900, 300, or 100 s of water access per trial) and amount of acquisition training (5 or 15 daily trials). With total amount of water access equated in acquisition, extinction with large rewards was faster (longer latencies in 900/5 than 300/15), but with total amount of training equated, extinction with small rewards was faster (longer latencies in 100/15 than 300/15). Experiment 2 varied reward magnitude (1200 or 120 s of water access per trial) while holding constant the number of acquisition trials (5 daily trials) and the duration of extinction trials (300 s). Extinction performance was lower with small, rather than large reward magnitude (longer latencies in 120/300 than in 1200/300). Thus, instrumental extinction depends upon the amount of time toads are exposed to the empty goal compartment during extinction trials.

  15. Optical Extinction and Aerosol Hygroscopicity in the Southeastern United States

    NASA Astrophysics Data System (ADS)

    Brock, C. A.; Gordon, T.; Wagner, N.; Lack, D. A.; Richardson, M.; Middlebrook, A. M.; Liao, J.; Murphy, D. M.; Attwood, A. R.; Washenfelder, R. A.; Campuzano Jost, P.; Day, D. A.; Jimenez, J. L.; Carlton, A. M. G.

    2015-12-01

    Most aerosol particles take up water and grow as relative humidity increases, leading to increased optical extinction, reduced visibility, greater aerosol optical depths (AODs), and altered radiative forcing, even while dry particulate mass remains constant. Relative humidity varies greatly temporally, horizontally, and especially vertically. Thus hygroscopicity is a confounding factor when attempting to link satellite-based observations of AOD to surface measurements of particulate mass or to model predictions of aerosol mass concentrations. Airborne observations of aerosol optical, chemical, and microphysical properties were made in the southeastern United States in the daytime in summer 2013 during the NOAA SENEX and NASA SEAC4RS projects. Applying κ-Köhler theory for hygroscopic growth to these data, the inferred hygroscopicity parameter κ for the organic fraction of the aerosol was <0.11. This κ for organics is toward the lower end of values found from laboratory studies of the aerosol formed from oxidation of biogenic precursors and from several field studies in rural environments. The gamma (γ) parameterization is commonly used to describe the change in aerosol extinction as a function of relative humidity. Because this formulation did not fit the airborne data well, a new parameterization was developed that better describes the observations. This new single-parameter κext formulation is physically based and relies upon the well-known approximately linear relationship between particle volume and optical extinction. The fitted parameter, κext, is nonlinearly related to the chemically derived κ parameter used in κ-Köhler theory. The values of κext determined from the airborne measurements are consistent with independent observations at a nearby ground site.

  16. Protection from extinction.

    PubMed

    Rescorla, Robert A

    2003-05-01

    The effect of the presence of a conditioned inhibitor on extinction of excitatory conditioning was studied in one magazine approach and three autoshaping experiments using rats and pigeons. In each case, the presence of an inhibitor reduced responding to an exciter during extinction but allowed substantial recovery of responding to that exciter when subsequently tested separately. Control stimuli with a history of being irrelevant to reinforcement or being nonreinforced had less of a protective effect. This constitutes a clear demonstration of protection from extinction, a phenomenon of substantial theoretical and applied importance.

  17. Holocene extinction dynamics of Equus hydruntinus, a late-surviving European megafaunal mammal

    NASA Astrophysics Data System (ADS)

    Crees, Jennifer J.; Turvey, Samuel T.

    2014-05-01

    The European wild ass (Equus hydruntinus) is a globally extinct Eurasian equid. This species was widespread in Europe and southwest Asia during the Late Pleistocene, but its distribution became restricted to southern Europe and adjacent geographic regions in the Holocene. Previous research on E. hydruntinus has focused predominantly on its taxonomy and Late Pleistocene distribution. However, its Holocene distribution and extinction remain poorly understood, despite the fact that the European wild ass represents one of Europe's very few globally extinct Holocene megafaunal mammal species. We summarise all available Holocene zooarchaeological spatio-temporal occurrence data for the species, and analyse patterns of its distribution and extinction using point pattern analysis (kernel density estimation and Clark Evans index) and optimal linear estimation. We demonstrate that the geographic range of E. hydruntinus became highly fragmented into discrete subpopulations during the Holocene, which were associated with separate regions of open habitat and which became progressively extinct between the Neolithic and Iron Age. These data challenge previous suggestions of the late survival of E. hydruntinus into the medieval period in Spain, and instead suggest that postglacial climate-driven vegetational changes were a primary factor responsible for extinction of the species, driving isolation of small remnant subpopulations that may have been increasingly vulnerable to human exploitation. This study contributes to a more nuanced understanding of Late Quaternary species extinctions in Eurasia, suggesting that they were temporally staggered and distinct in their respective extinction trajectories.

  18. Extinction and climate change.

    PubMed

    Thomas, Chris D; Williamson, Mark

    2012-02-22

    Arising from F. He & S. P. Hubbell 473, 368-371 (2011). Statistical relationships between habitat area and the number of species observed (species-area relationships, SARs) are sometimes used to assess extinction risks following habitat destruction or loss of climatic suitability. He and Hubbell argue that the numbers of species confined to-rather than observed in-different areas (endemics-area relationships, EARs) should be used instead of SARs, and that SAR-based extinction estimates in the literature are too high. We suggest that He and Hubbell's SAR estimates are biased, that the empirical data they use are not appropriate to calculate extinction risks, and that their statements about extinction risks from climate change do not take into account non-SAR-based estimates or recent observations. Species have already responded to climate change in a manner consistent with high future extinction risks.

  19. Erasing fear memories with extinction training

    PubMed Central

    Quirk, Gregory J.; Paré, Denis; Richardson, Rick; Herry, Cyril; Monfils, Marie H.; Schiller, Daniela; Vicentic, Aleksandra

    2012-01-01

    Decades of behavioral studies have confirmed that extinction does not erase classically-conditioned fear memories. For this reason, research efforts have focused on the mechanisms underlying the development of extinction-induced inhibition within fear circuits. However, recent studies in rodents have uncovered mechanisms that stabilize and destabilize fear memories, opening the possibility that extinction might be used to erase fear memories. This symposium focuses on several of these new developments, which involve the timing of extinction training. Extinction-induced erasure of fear occurs in very young rats, but is lost with the development of perineuronal nets in the amygdala that render fear memories impervious to extinction. Moreover, extinction administered during the reconsolidation phase, when fear memory is destabilized, updates the fear association as safe, thereby preventing the return of fear, in both rats and humans. The use of modified extinction protocols to eliminate fear memories complements existing pharmacological strategies for strengthening extinction. PMID:21068303

  20. End-Permian mass extinction and palaeoenvironmental changes in Neotethys: Evidence from an oceanic carbonate section in southwestern Tibet

    NASA Astrophysics Data System (ADS)

    Shen, Shu-zhong; Cao, Chang-qun; Zhang, Yi-chun; Li, Wen-zhong; Shi, G. R.; Wang, Yue; Wu, Ya-sheng; Ueno, K.; Henderson, C. M.; Wang, Xiang-dong; Zhang, Hua; Wang, Xiao-juan; Chen, Jun

    2010-08-01

    This paper documents a new Permian-Triassic carbonate sequence which recorded the end-Permian mass extinction in the isolated oceanic setting of Neotethys in southwestern Tibet, China. The sequence is over 350 m thick and consists of the Gyanyima and the Lower Lanchengquxia formations in ascending order. The Lopingian (Late Permian) Gyanyima Formation is composed of fossiliferous reddish carbonates dominated by Colaniella grainstone and reef facies including fenestrate/sponge/coral framestone and bafflestone. 156 species are recognized from the Lopingian Gyanyima Formation. Composite ranges of brachiopods, ostracods, rugose corals and foraminifers at the Gyanyima Section suggest that evolution and diversification of Permian marine organisms continued to the end-Permian preceding a major faunal extinction close to the Permian-Triassic boundary (PTB), coincident with a 2-3‰ negative shift of δ13C carb. The timing and accelerating extinction pattern and the negative δ13C carb excursion are largely comparable with those reported from many previously-documented sections on continental shelf environments. Based on a detailed lithofacies analysis, the latest Permian reefal facies is sharply replaced by ostracod/crinoid packstone/grainstone with abrupt abundant occurrences of Early Triassic conodonts at the Gyanyima Section. This is then followed by thrombolitic microbialite, stromatolite, packstone containing abundant spherical microbes, and bivalve/ammonoid packstone of tidal and intertidal facies. This distinct lithofacies and biofacies shift would, therefore, suggest a dramatic faunal community and environmental change across the PTB. Distinct palaeoclimate fluctuations through the P- T interval are also indicated by the alternation of warm- and cool-water faunas through the uppermost part of the succession. The lower part of the Gyanyima Formation is characterized by a warm condition as indicated by Cathaysian-dominated fossils. This was then followed by a mild

  1. Rescaling of temporal expectations during extinction

    PubMed Central

    Drew, Michael R.; Walsh, Carolyn; Balsam, Peter D

    2016-01-01

    Previous research suggests that extinction learning is temporally specific. Changing the CS duration between training and extinction can facilitate the loss of the CR within the extinction session but impairs long-term retention of extinction. In two experiments using conditioned magazine approach with rats, we examined the relation between temporal specificity of extinction and CR timing. In Experiment 1 rats were trained on a 12-s, fixed CS-US interval and then extinguished with CS presentations that were 6, 12, or 24 s in duration. The design of Experi