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Sample records for antarctic fossil record

  1. Biomarkers and Microbial Fossils In Antarctic Rocks

    NASA Astrophysics Data System (ADS)

    Wierzchos, J.; Ascaso, C.

    Lithobiontic microbial communities living within Antarctic rocks are an example of survival in an extremely cold and dry environment. Any unfavourable change in ex- ternal conditions can result in the death and disappearance of microscopic organisms, and this may be followed by the appearance of trace biomarkers and microbial fossils. The extinction of these microorganisms in some zones of the Ross Desert, probably provoked by the hostile environment, might be considered a good terrestrial analogue of the first stage of the disappearance of possible life on early Mars. Granite samples from maritime Antarctica (Granite Harbour) and sandstone rocks from the continental Ross Desert were collected with the aim of searching for biomarkers and microbial fossils at the microscopic level of observation. To this end, a novel in situ applica- tion of scanning electron microscopy with backscattered electron imaging was com- bined with the simultaneous use of X-ray energy dispersive spectroscopy techniques. Our findings confirm the existence of inorganic biomarkers in the form of physico- chemically bioweathered minerals within the granitic rocks. The presence of Fe-rich diagenetic minerals, such as iron hydroxide nanocrystals and biogenic clays around chasmoendolithic hyphae and bacterial cells was also observed. Others biomarkers, including inorganic deposits such as calcium oxalates and silica accumulations, are clear signs of endolithic microorganism activity. The interior of the sandstone rocks (Ross Desert, Mt. Fleming) reveal the presence of microbial fossils of algae and other endolithic microorganisms. These microbial fossils, detected for the first time within Antarctic rocks, contain well preserved and morphologically distinguishable relics of ultrastructural cytoplasm elements, such as cell walls, chloroplast membranes, and oc- casionally, pyrenoids and traces of organic matter. These structures are similar to those observed in live cells also found in Antarctic

  2. Cosmogenic records in Antarctic meteorites

    NASA Technical Reports Server (NTRS)

    Goswami, J. N.; Nishiizumi, K.

    1983-01-01

    Aliquot samples of 29 Antarctic L and H chondrites are analyzed for their nuclear track records and Mn-53 activities. The track density in the analyzed samples ranges from 10 to the 4th to approximately 6 x 10 to the 6th per sq cm. A significant finding is the observation of track-rich grains in a set of four L3 chondrites (ALHA 77215, 77216, 77217, and 77252), suspected of belonging to the same fall based on petrographic observations. An additional sample, ALHA 78105, an L6 chondrite, also has track-rich grains. Mn-53 activity is at near saturation level in approximately 65 percent of the analyzed samples, suggesting exposure ages of greater than 10 m.y. in these cases. Very few H chondrites from the 7-m.y. exposure age peak are apparently sampled among the ones investigated in this study. Approximately 6 percent and 4 percent, respectively, of the Antarctic H and L chondrites analyzed thus far for their cosmogenic records have precompaction irradiation features. A combined analysis of Mn-53 and nuclear track data makes it possible to confirm or rule out the proposed pairing of several sets of Antarctic meteorites and to estimate the preatmospheric sizes of some of these meteorites. The results suggest that most of the small Antarctic meteorites (less than 1 kg) have suffered high (greater than 95 percent) ablation mass-loss.

  3. Microbial trace-fossil formation, biogenous, and abiotic weathering in the Antarctic cold desert

    NASA Technical Reports Server (NTRS)

    Friedmann, E. Imre; Weed, Rebecca

    1987-01-01

    In the Antarctic cold desert (Ross Desert), the survival of the cryptoendolithic microorganisms that colonize the near-surface layer of porous sandstone rocks depends on a precarious equilibrium of biological and geological factors. An unfavorable shift of this equilibrium results in death, and this may be followed by formation of trace fossils that preserve the characteristic iron-leaching pattern caused by microbial activity. Similar microbial trace fossils may exist in the geological record. If life ever arose on early Mars, similar processes may have occurred there and left recognizable traces.

  4. 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.

  5. Organic molecules as chemical fossils - The molecular fossil record

    NASA Technical Reports Server (NTRS)

    Eglinton, G.

    1983-01-01

    The study of biochemical clues to the early earth and the origin of life is discussed. The methods used in such investigation are described, including the extraction, fractionation, and analysis of geolipids and the analysis of kerogen. The occurrence of molecular fossils in the geological record is examined, discussing proposed precursor-product relationships and the molecular assessment of deep sea sediments, ancient sediments, and crude petroleums. Alterations in the molecular record due to diagenesis and catagenesis are considered, and the use of microbial lipids as molecular fossils is discussed. The results of searches for molecular fossils in Precambrian sediments are assessed.

  6. The fossil record of the sixth extinction.

    PubMed

    Plotnick, Roy E; Smith, Felisa A; Lyons, S Kathleen

    2016-05-01

    Comparing the magnitude of the current biodiversity crisis with those in the fossil record is difficult without an understanding of differential preservation. Integrating data from palaeontological databases with information on IUCN status, ecology and life history characteristics of contemporary mammals, we demonstrate that only a small and biased fraction of threatened species (< 9%) have a fossil record, compared with 20% of non-threatened species. We find strong taphonomic biases related to body size and geographic range. Modern species with a fossil record tend to be large and widespread and were described in the 19(th) century. The expected magnitude of the current extinction based only on species with a fossil record is about half of that of one based on all modern species; values for genera are similar. The record of ancient extinctions may be similarly biased, with many species having originated and gone extinct without leaving a tangible record. PMID:26932459

  7. Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf

    NASA Astrophysics Data System (ADS)

    Clark, Nicola A.; Williams, Mark; Hill, Daniel J.; Quilty, Patrick G.; Smellie, John L.; Zalasiewicz, Jan; Leng, Melanie J.; Ellis, Michael A.

    2013-08-01

    We evaluate the available palaeontological and geochemical proxy data from bivalves, bryozoans, silicoflagellates, diatoms and cetaceans for sea surface temperature (SST) regimes around the nearshore Antarctic coast during the late Neogene. These fossils can be found in a number of shallow marine sedimentary settings from three regions of the Antarctic continent, the northern Antarctic Peninsula, the Prydz Bay region and the western Ross Sea. Many of the proxies suggest maximum spring-summer SSTs that are warmer than present by up to 5 °C, which would result in reduced seasonal sea ice. The evidence suggests that the summers on the Antarctic shelf during the late Neogene experienced most of the warming, while winter SSTs were little changed from present. Feedbacks from changes in summer sea ice cover may have driven much of the late Neogene ocean warming seen in stratigraphic records. Synthesized late Neogene and earliest Quaternary Antarctic shelf proxy data are compared to the multi-model SST estimates of the Pliocene Model Intercomparison Project (PlioMIP) Experiment 2. Despite the fragmentary geographical and temporal context for the SST data, comparisons between the SST warming in each of the three regions represented in the marine palaeontological record of the Antarctic shelf and the PlioMIP climate simulations show a good concordance.

  8. Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf.

    PubMed

    Clark, Nicola A; Williams, Mark; Hill, Daniel J; Quilty, Patrick G; Smellie, John L; Zalasiewicz, Jan; Leng, Melanie J; Ellis, Michael A

    2013-08-01

    We evaluate the available palaeontological and geochemical proxy data from bivalves, bryozoans, silicoflagellates, diatoms and cetaceans for sea surface temperature (SST) regimes around the nearshore Antarctic coast during the late Neogene. These fossils can be found in a number of shallow marine sedimentary settings from three regions of the Antarctic continent, the northern Antarctic Peninsula, the Prydz Bay region and the western Ross Sea. Many of the proxies suggest maximum spring-summer SSTs that are warmer than present by up to 5 °C, which would result in reduced seasonal sea ice. The evidence suggests that the summers on the Antarctic shelf during the late Neogene experienced most of the warming, while winter SSTs were little changed from present. Feedbacks from changes in summer sea ice cover may have driven much of the late Neogene ocean warming seen in stratigraphic records. Synthesized late Neogene and earliest Quaternary Antarctic shelf proxy data are compared to the multi-model SST estimates of the Pliocene Model Intercomparison Project (PlioMIP) Experiment 2. Despite the fragmentary geographical and temporal context for the SST data, comparisons between the SST warming in each of the three regions represented in the marine palaeontological record of the Antarctic shelf and the PlioMIP climate simulations show a good concordance. PMID:23828612

  9. Antarctic glacial geologic record and GCM modeling: A test

    SciTech Connect

    Elliot, D.H.; Bromwich, D.H.; Harwood, D.M.; Webb, P.

    1992-03-01

    A recent GCM (General Circulation Model) study of Antarctic glaciation by Oglesby concluded that (1) oceanic heat transport is relatively unimportant in the development and maintenance of Antarctic glaciation; (2) height and polar position, not the Antarctic Circumpolar Current, have led to thermal isolation; and (3) surface elevation may be crucial for glaciation. Model results are here evaluated against the Pliocene geologic record for Antarctica. The Sirius Group, widely distributed in the Transantarctic Mountains, contains diatom floras suggesting open marine conditions in interior East Antarctica as recently as about 3 m.y. ago. The Sirius deposits also contain a sparse fossil flora including Nothofagus wood, demonstrating snow-free conditions and elevated summer temperatures within 500 km of the South Pole. Based on fission track data and marine sediments, uplift rates for the Transantarctic Mountains are estimated to average 50-100 m m.y.-1 for the last 10 m.y., although rates may have been higher during the last 3 m.y. The continental interior is also most unlikely to have changed elevation by more than a few hundred meters in the last 3 m.y. If the dating of the Sirius is correct and uplift rates have not been an order of magnitude higher, then polar location and elevation cannot be primary controls on the formation and subsequent fluctuations of the ice sheet.

  10. Reconciling molecular phylogenies with the fossil record.

    PubMed

    Morlon, Hélène; Parsons, Todd L; Plotkin, Joshua B

    2011-09-27

    Historical patterns of species diversity inferred from phylogenies typically contradict the direct evidence found in the fossil record. According to the fossil record, species frequently go extinct, and many clades experience periods of dramatic diversity loss. However, most analyses of molecular phylogenies fail to identify any periods of declining diversity, and they typically infer low levels of extinction. This striking inconsistency between phylogenies and fossils limits our understanding of macroevolution, and it undermines our confidence in phylogenetic inference. Here, we show that realistic extinction rates and diversity trajectories can be inferred from molecular phylogenies. To make this inference, we derive an analytic expression for the likelihood of a phylogeny that accommodates scenarios of declining diversity, time-variable rates, and incomplete sampling; we show that this likelihood expression reliably detects periods of diversity loss using simulation. We then study the cetaceans (whales, dolphins, and porpoises), a group for which standard phylogenetic inferences are strikingly inconsistent with fossil data. When the cetacean phylogeny is considered as a whole, recently radiating clades, such as the Balaneopteridae, Delphinidae, Phocoenidae, and Ziphiidae, mask the signal of extinctions. However, when isolating these groups, we infer diversity dynamics that are consistent with the fossil record. These results reconcile molecular phylogenies with fossil data, and they suggest that most extant cetaceans arose from four recent radiations, with a few additional species arising from clades that have been in decline over the last ~10 Myr. PMID:21930899

  11. Reconciling molecular phylogenies with the fossil record

    PubMed Central

    Morlon, Hélène; Parsons, Todd L.; Plotkin, Joshua B.

    2011-01-01

    Historical patterns of species diversity inferred from phylogenies typically contradict the direct evidence found in the fossil record. According to the fossil record, species frequently go extinct, and many clades experience periods of dramatic diversity loss. However, most analyses of molecular phylogenies fail to identify any periods of declining diversity, and they typically infer low levels of extinction. This striking inconsistency between phylogenies and fossils limits our understanding of macroevolution, and it undermines our confidence in phylogenetic inference. Here, we show that realistic extinction rates and diversity trajectories can be inferred from molecular phylogenies. To make this inference, we derive an analytic expression for the likelihood of a phylogeny that accommodates scenarios of declining diversity, time-variable rates, and incomplete sampling; we show that this likelihood expression reliably detects periods of diversity loss using simulation. We then study the cetaceans (whales, dolphins, and porpoises), a group for which standard phylogenetic inferences are strikingly inconsistent with fossil data. When the cetacean phylogeny is considered as a whole, recently radiating clades, such as the Balaneopteridae, Delphinidae, Phocoenidae, and Ziphiidae, mask the signal of extinctions. However, when isolating these groups, we infer diversity dynamics that are consistent with the fossil record. These results reconcile molecular phylogenies with fossil data, and they suggest that most extant cetaceans arose from four recent radiations, with a few additional species arising from clades that have been in decline over the last ∼10 Myr. PMID:21930899

  12. The circum-Antarctic sedimentary record; a dowsing rod for Antarctic ice in the Eocene

    NASA Astrophysics Data System (ADS)

    Scher, H.

    2012-12-01

    Arguments for short-lived Antarctic glacial events during the Eocene (55-34 Ma) are compelling, however the paleoceanographic proxy records upon which these arguments are based (e.g., benthic δ18O, eustatic sea level, deep sea carbonate deposition) are global signals in which the role of Antarctic ice volume variability is ambiguous. That is to say, the proxy response to ice volume may be masked other processes. As a result broad correlations between proxies for ice volume are lacking during suspected Eocene glacial events. I will present a more direct approach for detecting Antarctic ice sheets in the Eocene; utilizing provenance information derived from the radiogenic isotopic composition of the terrigenous component of marine sediments near Antarctica. The method relies on knowledge that marine sediments represent a mixture derived from different basement terrains with different isotopic fingerprints. A key issue when using sedimentary deposits to characterize continental sediment sources is to deconvolve different sources from the mixed signal of the bulk sample. The pioneering work of Roy et al. (2007) and van de Flierdt et al. (2007) represents a major advance in Antarctic provenance studies. It is now known that the isotopic composition of neodymium (Nd) and hafnium (Hf) in modern circum-Antarctic sediments are distributed in a pattern that mimics the basement age of sediment sources around Antarctica. For this study I selected two Ocean Drilling Program (ODP) sites on southern Kerguelen Plateau (ODP Sites 738 and 748) because of their proximity to Prydz Bay, where Precambrian sediment sources contribute to extremely nonradiogenic isotopic signatures in modern sediments in the Prydz Bay region. New detrital Nd isotope records from these sediment cores reveal an Nd isotope excursion at the Bartonian/Priabonian boundary (ca. 37 Ma) that coincides with a 0.5 ‰ increase in benthic foram δ18O values. Detrital sediment ɛNd values are around -12 in intervals

  13. Insect diversity in the fossil record

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    Insects possess a surprisingly extensive fossil record. Compilation of the geochronologic ranges of insect families demonstrates that their diversity exceeds that of preserved vertebrate tetrapods through 91 percent of their evolutionary history. The great diversity of insects was achieved not by high origination rates but rather by low extinction rates comparable to the low rates of slowly evolving marine invertebrate groups. The great radiation of modern insects began 245 million years ago and was not accelerated by the expansion of angiosperms during the Cretaceous period. The basic trophic machinery of insects was in place nearly 100 million years before angiosperms appeared in the fossil record.

  14. Expected anomalies in the fossil record.

    PubMed

    Fischer, Mareike; Steel, Mike

    2008-01-01

    The problem of intermediates in the fossil record has been frequently discussed ever since Darwin. The extent of 'gaps' (missing transitional stages) has been used to argue against gradual evolution from a common ancestor. Traditionally, gaps have often been explained by the improbability of fossilization and the discontinuous selection of found fossils. Here we take an analytical approach and demonstrate why, under certain sampling conditions, we may not expect intermediates to be found. Using a simple null model, we show mathematically that the question of whether a taxon sampled from some time in the past is likely to be morphologically intermediate to other samples (dated earlier and later) depends on the shape and dimensions of the underlying phylogenetic tree that connects the taxa, and the times from which the fossils are sampled. PMID:19204808

  15. Adaptation, plant evolution, and the fossil record

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Niklas, K. J.

    1987-01-01

    The importance of adaptation in determining patterns of evolution has become an important focus of debate in evolutionary biology. As it pertains to paleobotany, the issue is whether or not adaptive evolution mediated by natural selection is sufficient to explain the stratigraphic distributions of taxa and character states observed in the plant fossil record. One means of addressing this question is the functional evaluation of stratigraphic series of plant organs set in the context of paleoenvironmental change and temporal patterns of floral composition within environments. For certain organ systems, quantitative estimates of biophysical performance can be made on the basis of structures preserved in the fossil record. Performance estimates for plants separated in time or space can be compared directly. Implicit in different hypotheses of the forces that shape the evolutionary record (e.g. adaptation, mass extinction, rapid environmental change, chance) are predictions about stratigraphic and paleoenvironmental trends in the efficacy of functional performance. Existing data suggest that following the evolution of a significant structural innovation, adaptation for improved functional performance can be a major determinant of evolutionary changes in plants; however, there are structural and development limits to functional improvement, and once these are reached, the structure in question may no longer figure strongly in selection until and unless a new innovation evolves. The Silurian-Devonian paleobotanical record is consistent with the hypothesis that the succession of lowland floodplain dominants preserved in the fossil record of this interval was determined principally by the repeated evolution of new taxa that rose to ecological importance because of competitive advantages conferred by improved biophysical performance. This does not seem to be equally true for Carboniferous-Jurassic dominants of swamp and lowland floodplain environments. In these cases

  16. Combustion of available fossil-fuel resources sufficient to eliminate the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Winkelmann, R.; Levermann, A.; Ridgwell, A.; Caldeira, K.

    2015-12-01

    The Antarctic Ice Sheet stores water equivalent to 58 meters in global sea-level rise. Here we show in simulations with the Parallel Ice Sheet Model that burning the currently attainable fossil-fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil-fuel emissions of 10 000 GtC, Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 meters per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West- and East Antarctica results in a threshold-increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.

  17. Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet.

    PubMed

    Winkelmann, Ricarda; Levermann, Anders; Ridgwell, Andy; Caldeira, Ken

    2015-09-01

    The Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources. PMID:26601273

  18. Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet

    PubMed Central

    Winkelmann, Ricarda; Levermann, Anders; Ridgwell, Andy; Caldeira, Ken

    2015-01-01

    The Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources. PMID:26601273

  19. Sei whale sounds recorded in the Antarctic.

    PubMed

    McDonald, Mark A; Hildebrand, John A; Wiggins, Sean M; Thiele, Deborah; Glasgow, Deb; Moore, Sue E

    2005-12-01

    Sei whales are the least well known acoustically of all the rorquals, with only two brief descriptions of their calls previously reported. Recordings of low-frequency tonal and frequency swept calls were made near a group of four or five sei whales in waters west of the Antarctic Peninsula on 19 February 2003. These whales also produced broadband sounds which can be described as growls or whooshes. Many of the tonal and frequency swept calls (30 out of 68) consist of multiple parts with a frequency step between the two parts, this being the most unique characteristic of the calls, allowing them to be distinguished from the calls of other whale species. The average duration of the tonal calls is 0.45 +/- 0.3 s and the average frequency is 433 +/- 192 Hz. Using a calibrated seafloor recorder to determine the absolute calibration of a sonobuoy system, the maximum source level of the tonal calls was 156 +/- 3.6 dB re 1 microPa at 1 m. Each call had different character and there was no temporal pattern in the calling. PMID:16419837

  20. Sei whale sounds recorded in the Antarctic

    NASA Astrophysics Data System (ADS)

    McDonald, Mark A.; Hildebrand, John A.; Wiggins, Sean M.; Thiele, Deborah; Glasgow, Deb; Moore, Sue E.

    2005-12-01

    Sei whales are the least well known acoustically of all the rorquals, with only two brief descriptions of their calls previously reported. Recordings of low-frequency tonal and frequency swept calls were made near a group of four or five sei whales in waters west of the Antarctic Peninsula on 19 February 2003. These whales also produced broadband sounds which can be described as growls or whooshes. Many of the tonal and frequency swept calls (30 out of 68) consist of multiple parts with a frequency step between the two parts, this being the most unique characteristic of the calls, allowing them to be distinguished from the calls of other whale species. The average duration of the tonal calls is 0.45+/-0.3 s and the average frequency is 433+/-192 Hz. Using a calibrated seafloor recorder to determine the absolute calibration of a sonobuoy system, the maximum source level of the tonal calls was 156+/-3.6 dB re 1 μPa at 1 m. Each call had different character and there was no temporal pattern in the calling.

  1. Towards a Circum-Antarctic Holocene Paleointensity Record

    NASA Astrophysics Data System (ADS)

    Brachfeld, S.; Kissel, C.; Laj, C.; Willmott, V.

    2005-12-01

    New Holocene geomagnetic paleointensity records have been constructed from the Western Antarctic Peninsula (WAP), Eastern Antarctic Peninsula (EAP), and from the East Antarctic Margin (EAM). The goal of this work is to develop Antarctic paleointensity reference curves for correlation and dating of Antarctic continental shelf sediments. Sediment sequences deposited in fjords and inner shelf basins contain Holocene sections of 3-meters to more than 20-meters, recording the last deglaciation, the paleohistory of ice shelves, and shifting paleoceanographic conditions. However, these records suffer from a lack biogenic calcite for radiocarbon dating. Diatomaceous mud contains sufficient acid insoluble organic matter (aiom) for radiocarbon dating and hence an independent chronology. However, laminated oozes yield shallow inclinations, hence the remanence vector is suspect. Bioturbated diatomaceous mud and diatom-poor muds yield excellent directional records and satisfy the criteria for magnetic uniformity, however the organic content is low and aiom dates can be problematic. Our paleointensity records show the broad pattern of higher intensity during the late Holocene, and lower intensity during the early to middle Holocene, similar to the sinusoidal intensity pattern seen in global absolute and relative paleointensity stacks. Several of the records contain 3 to 4 late Holocene peaks with 1000-year wavelengths that are similar in amplitude and duration to features seen in northern hemisphere lacustrine and marine records. Here we evaluate the local versus regional character of the Antarctic paleointensity records, and the consistency of aiom-dated versus paleointensity-tuned chronologies.

  2. Organo-mineral imprints in fossil cyanobacterial mats of an Antarctic lake

    NASA Astrophysics Data System (ADS)

    Javaux, E.; Lepot, K.; Deremiens, L.; Namsaraev, Z.; Compere, P.; Gerard, E.; Verleyen, E.; Tavernier, I.; Hodgson, D.; Vyverman, W.; Wilmotte, A.

    2010-12-01

    Lacustrine microbial mats in Antarctic ice-free oases are considered to be modern analogues of early microbial ecosystems because they are dominated by cyanobacteria that need to cope with elevated UV radiation during summer by producing protective compounds such as UV-screening pigments. These microbial consortia offer a unique opportunity to (i) identify biogeochemical signatures to study the fossil record of microorganisms, and (ii) better understand their imprint mineral record. We studied sediment cores from a meromictic brackish-water lake, Kobachi Ike, Skarvsnes Peninsula, Lützow Holm Bay, East Antarctica, where primary production is dominated by photosynthetic benthic communities. The faintly to finely laminated (stromatolitic) sediments include variable amounts of organic-rich laminae, micritic carbonate, clays and silicate sand. We studied the microstructure and chemistry of organo-mineral associations in a suite of sediments ranging in age from several tens to ca. 3500 years. We examined Os- and U- stained polished resin-embedded sediments in a scanning electron microscope (SEM). We imaged photosynthetic pigments of microorganisms in fluorescence by confocal laser scanning microscopy (CLSM). We analyzed organic matter chemistry in demineralized sediments and cultured cyanobacteria using Fourier-Transform Infrared (FTIR) spectromicroscopy. Molecular analyses of fossil cyanobacterial DNA were performed using Denaturating Gradient Gel Electrophoresis of partial 16S rRNA genes and sequencing. SEM revealed an intimate association between nanostructured Ca-carbonate peloids, fossil cell clusters resembling colonies of unicellular coccoid cyanobacteria, and cell-like imprints preserved in nanocarbonates. Diffuse organic matter (kerogen or EPS) is associated with nanoclays to form a laminae-building network around the carbonates. These organo-mineral microstructures strongly resemble those of the 2.7 Gyrs old Tumbiana stromatolites. CLSM imaging and fossil DNA

  3. The eukaryotic fossil record in deep time

    NASA Astrophysics Data System (ADS)

    Butterfield, N.

    2011-12-01

    Eukaryotic organisms are defining constituents of the Phanerozoic biosphere, but they also extend well back into the Proterozoic record, primarily in the form of microscopic body fossils. Criteria for identifying pre-Ediacaran eukaryotes include large cell size, morphologically complex cell walls and/or the recognition of diagnostically eukaryotic cell division patterns. The oldest unambiguous eukaryote currently on record is an acanthomorphic acritarch (Tappania) from the Palaeoproterozoic Semri Group of central India. Older candidate eukaryotes are difficult to distinguish from giant bacteria, prokaryotic colonies or diagenetic artefacts. In younger Meso- and Neoproterozoic strata, the challenge is to recognize particular grades and clades of eukaryotes, and to document their macro-evolutionary expression. Distinctive unicellular forms include mid-Neoproterozoic testate amoebae and phosphate biomineralizing 'scale-microfossils' comparable to an extant green alga. There is also a significant record of seaweeds, possible fungi and problematica from this interval, documenting multiple independent experiments in eukaryotic multicellularity. Taxonomically resolved forms include a bangiacean red alga and probable vaucheriacean chromalveolate algae from the late Mesoproterozoic, and populations of hydrodictyacean and siphonocladalean green algae of mid Neoproterozoic age. Despite this phylogenetic breadth, however, or arguments from molecular clocks, there is no convincing evidence for pre-Ediacaran metazoans or metaphytes. The conspicuously incomplete nature of the Proterozoic record makes it difficult to resolve larger-scale ecological and evolutionary patterns. Even so, both body fossils and biomarker data point to a pre-Ediacaran biosphere dominated overwhelming by prokaryotes. Contemporaneous eukaryotes appear to be limited to conspicuously shallow water environments, and exhibit fundamentally lower levels of morphological diversity and evolutionary turnover than

  4. Rates of speciation in the fossil record

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    Data from palaeontology and biodiversity suggest that the global biota should produce an average of three new species per year. However, the fossil record shows large variation around this mean. Rates of origination have declined through the Phanerozoic. This appears to have been largely a function of sorting among higher taxa (especially classes), which exhibit characteristic rates of speciation (and extinction) that differ among them by nearly an order of magnitude. Secular decline of origination rates is hardly constant, however; many positive deviations reflect accelerated speciation during rebounds from mass extinctions. There has also been general decline in rates of speciation within major taxa through their histories, although rates have tended to remain higher among members in tropical regions. Finally, pulses of speciation appear sometimes to be associated with climate change, although moderate oscillations of climate do not necessarily promote speciation despite forcing changes in species' geographical ranges.

  5. Meteoritic event recorded in Antarctic ice

    SciTech Connect

    Harvey, R.P.; Dunbar, N.W.; McIntosh, W.C.; Esser, R.P.; Nishiizumi, Kuni; Taylor, S.; Caffee, M.W.

    1998-07-01

    During systematic sampling of volcanic ash (tephra) layers at a well-known Antarctic meteorite collection site (the Allan Hills main ice field), a band of unusually dark and rounded (many spheroidal) particles was discovered. This debris layer (BIT-58) extends parallel to the stratigraphy of the ice established from the tephra bands, apparently marking a single depositional event. The shapes, internal texture, major element composition, and levels of cosmogenic nuclides of particles from within BIT-58 all strongly suggest that this material represents ablation debris from the passage of a large H-group ordinary chondrite. Preliminary cosmogenic isotope dating suggests an age of 2.8 Ma, implying that the East Antarctic ice sheet has been stable since that time. The relationship of the Bit-58 layer to known impact events is not clear.

  6. The Quaternary fossil-pollen record and global change

    SciTech Connect

    Grimm, E.C. . Research and Collections Center)

    1993-03-01

    Fossil pollen provide one of the most valuable records of vegetation and climate change during the recent geological past. Advantages of the fossil-pollen record are that deposits containing fossil pollen are widespread, especially in areas having natural lakes, that fossil pollen occurs in continuous stratigraphic sequences spanning millennia, and that fossil pollen occurs in quantitative assemblages permitting a multivariate approach for reconstructing past vegetation and climates. Because of stratigraphic continuity, fossil pollen records climate cycles on a wide range of scales, from annual to the 100 ka Milankovitch cycles. Receiving particular emphasis recently are decadal to century scale changes, possible from the sediments of varved lakes, and late Pleistocene events on a 5--10 ka scale possibly correlating with the Heinrich events in the North Atlantic marine record or the Dansgaard-Oeschger events in the Greenland ice-core record. Researchers have long reconstructed vegetation and climate by qualitative interpretation of the fossil-pollen record. Recently quantitative interpretation has developed with the aid of large fossil-pollen databases and sophisticated numerical models. In addition, fossil pollen are important climate proxy data for validating General Circulation Models, which are used for predicting the possible magnitude future climate change. Fossil-pollen data also contribute to an understanding of ecological issues associated with global climate change, including questions of how and how rapidly ecosystems might respond to abrupt climate change.

  7. Special Creation and the Fossil Record: The Central Fallacy.

    ERIC Educational Resources Information Center

    Miller, Kenneth R.

    1982-01-01

    Fossil records are used to point out two major flaws in the scientific creationist theory: (1) factual evidence does not support the theory, and (2) the creationists' own characterization of the fossil record contradicts their theory. Claims that creationists avoid discussing specifics about their model because of weaknesses. (DC)

  8. Reconstructions of Late Holocene Climate Using Ice-entombed Mosses and Sub-fossil Peat on the Western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Yu, Zicheng; Loisel, Julie; Beilman, David; Cleary, Kate

    2015-04-01

    The western Antarctic Peninsula (WAP) is one of three regions on Earth that have experienced the greatest warming over recent decades. Here we used paleo records from fossil mosses and peats on the WAP to explore a new paleoclimate archive that links climate, cryosphere and ecosystem dynamics for reconstructing climate change in recent millennia. Continuing retreat of ice and permanent snow has recently exposed numerous entombed mosses and intact peatbank ecosystems along the WAP around 65°S latitude that have been buried under ice and snow during the cold "Little Ice Age" (LIA). Radiocarbon dating indicates ages of 850-600 cal yr BP from re-exposed moss samples from retreating ice and of 100 cal yr BP from near shrinking snow. This age difference suggests that initial climate cooling and subsequent ice advance overran peatbanks immediately below the ice margin at the onset of the LIA, followed by permanent snow expansion often from low elevation upslope at the end of the LIA. Furthermore, detailed macrofossil and pollen analysis of a peat core from a moss peatbank on nearby mainland Antarctic Peninsula show dramatic shifts from a waterlogged peatland dominated by pure stands of Antarctic hairgrass (Deschampsia antarctica) before the LIA at 2400-600 cal yr BP to an aerobic peatbank dominated by erect mosses Polytrichum strictum and Chorisodontium aciphyllum in the last 50 years. At present the nearest known occurrence of Deschampsia "bog peats" is in South Georgia, about 1900 km north at 54°S, a location having a mean annual temperature 6°C higher than the study region on the WAP. If we use this modern spatial relationship as an analogue, then this suggests that the climate a few centuries ago was much warmer (up to 6°C) than today and supported very different ecosystems on the WAP. Our results show that these re-exposed sub-fossil mosses and peats are potentially very useful for the reconstructions of coastal low-elevation terrestrial climates. These records

  9. Antarctic Cenozoic climate history from sedimentary records: ANDRILL and beyond.

    PubMed

    McKay, R M; Barrett, P J; Levy, R S; Naish, T R; Golledge, N R; Pyne, A

    2016-01-28

    Mounting evidence from models and geological data implies that the Antarctic Ice Sheet may behave in an unstable manner and retreat rapidly in response to a warming climate, which is a key factor motivating efforts to improve estimates of Antarctic ice volume contributions to future sea-level rise. Here, we review Antarctic cooling history since peak temperatures of the Middle Eocene Climatic Optimum (approx. 50 Ma) to provide a framework for future initiatives to recover sediment cores from subglacial lakes and sedimentary basins in Antarctica's continental interior. While the existing inventory of cores has yielded important insights into the biotic and climatic evolution of Antarctica, strata have numerous and often lengthy time breaks, providing a framework of 'snapshots' through time. Further cores, and more work on existing cores, are needed to reconcile Antarctic records with the more continuous 'far-field' records documenting the evolution of global ice volume and deep-sea temperature. To achieve this, we argue for an integrated portfolio of drilling and coring missions that encompasses existing methodologies using ship- and sea-ice-/ice-shelf-based drilling platforms as well as recently developed seafloor-based drilling and subglacial access systems. We conclude by reviewing key technological issues that will need to be overcome. PMID:26667911

  10. Fossil DNA as a Recorder of Ancient Microbial Communities and Palaeoenvironments

    NASA Astrophysics Data System (ADS)

    Coolen, M. J.; Boere, A.; Abbas, B.; Muyzer, G.; Overmann, J.; Wakeham, S. G.; Volkman, J. K.; Sinninghe Damste, J. S.

    2005-12-01

    Fossilized organic components provide an archive of ancient aquatic microbial communities and, hence, can be used to reconstruct climate-induced environmental changes and their impacts on biodiversity. However, the interpretation of these data is complicated by the limited source specificity of some traditional biomarkers, such as lipids and pigments. The ultimate biomarkers are genes encoding for ribosomal RNA (rDNA), which sequences provide information at the species level by phylogenetic comparison but until recently was only applied to identify extant species within environmental samples. With the exception of excellent preservation conditions prevailing in permafrost sediments (3), it was generally believed that DNA becomes rapidly degraded within fossil records. However, we have recently shown that especially in the presence of hydrogen sulfide, DNA can survive in the Holocene fossil record (1, 2). In this presentation we will show how, and to what extent, fossil DNA extracted from Holocene sediments of stratified lakes (the Canadian Mahoney Lake and the Antarctic Ace Lake) and the deep-sea (Black Sea) can be used as a novel proxy to reconstruct the ancient palaeodepositional environments and evolution of past microbial communities. In addition, we will discuss the fate of fossil DNA; quantitative stratigraphic analysis of lipid biomarkers and rDNA from the same biological precursors revealed information on the survival of fossil DNA in comparison to lipid biomarkers. It was shown that most of the DNA was degraded before dead cells reach the bottom but the remaining part was found to be well protected and even less prone to diagenetic alteration compared to certain lipid biomarkers. Base-pair compositions did not change during the Holocene, however, the fossil DNA became fragmented after several thousands of years of deposition but without significantly biasing the qualitative and quantitative molecular biological analysis of at least 10-ka-old fossil DNA

  11. The diatom record from beneath the West Antarctic Ice Sheet and the global proxy perspective

    NASA Technical Reports Server (NTRS)

    Scherer, Reed P.

    1993-01-01

    Recent glaciological evaluation and modeling of the marine-based West Antarctic Ice Sheet (WAIS) support the possibility that the WAIS disintegrated during one or more Pleistocene interglacial period(s). The magnitude of sea level and oxygen isotope variation during certain late-Pleistocene interglacial periods is also consistent with the possibility of major retreat of the WAIS. Although oxygen isotopes from deep-sea sediments provide the best available proxy record for global ice volume (despite the ambiguities in the record), the source of ice volume changes must be hypothesized. Based on the intensity of interglacial isotopic shifts recorded in Southern Ocean marine sedimentary records, stage 11 (400,000 years ago) is the strongest candidate for WAIS collapse, but the records for stages 9, 7, and 5.5 are all consistent with the possibility of multiple late-Pleistocene collapses. Seismic reflection studies through the WAIS have revealed thick successions of strata with seismic characteristics comparable to upper Tertiary marine sediments. Small samples of glacial diamictons from beneath the ice sheet have been collected via hot-water drilled access holes. These sediments include mixed diatom assemblages of varying ages. Late-Miocene diatoms dominate many samples, probably reflecting marine deposition in West Antarctic basins prior to development of a dominantly glacial phase in West Antarctica. In addition to late-Miocene diatoms, samples from Upstream B (1988/89) contain rare post-Miocene diatoms, many of which imply deposition in the West Antarctic interior during one or more Pleistocene deglaciation periods. Age-diagnostic fossils in glacial sediments beneath ice sheets provide relatively coarse chronostratigraphic control, but they do contain direct evidence of regional deglaciation. Thus, sub-glacial till samples provide the evidence regarding the source of ice sheet variability seen in well-dated proxy records. Combined, these independent data sets can

  12. Early East Antarctic Ice Sheet growth recorded in the landscape of the Gamburtsev Subglacial Mountains

    NASA Astrophysics Data System (ADS)

    Rose, Kathryn C.; Ferraccioli, Fausto; Jamieson, Stewart S. R.; Bell, Robin E.; Corr, Hugh; Creyts, Timothy T.; Braaten, David; Jordan, Tom A.; Fretwell, Peter T.; Damaske, Detlef

    2013-08-01

    The Gamburtsev Subglacial Mountains are regarded as a key nucleation site for the Antarctic Ice Sheet and they retain a unique long-term record of pre-glacial and early glacial landscape evolution. Here, we use a range of morphometric analyses to constrain the nature of early glaciation and subsequent ice sheet evolution in the interior of East Antarctica, using a new digital elevation model of the Gamburtsev Subglacial Mountains, derived from an extensive airborne radar survey. We find that an inherited fluvial landscape confirms the existence of the Gamburtsev Subglacial Mountains prior to the onset of glaciation at the Eocene-Oligocene climate boundary (ca. 34 Ma). Features characteristic of glaciation, at a range of scales, are evident across the mountains. High elevation alpine valley heads, akin to cirques, identified throughout the mountains, are interpreted as evidence for early phases of glaciation in East Antarctica. The equilibrium line altitudes associated with these features, combined with information from fossil plant assemblages, suggest that they formed at, or prior to, 34 Ma. It cannot be ruled out that they may have been eroded by ephemeral ice between the Late Cretaceous and the Eocene (100-34 Ma). Hanging valleys, overdeepenings, truncated spurs and steep-sided, linear valley networks are indicative of a more widespread alpine glaciation in this region. These features represent ice growth at, or before, 33.7 Ma and provide a minimum estimate for the scale of the East Antarctic Ice Sheet between ca. 34 and 14 Ma, when dynamic fluctuations in ice extent are recorded at the coast of Antarctica. The implications are that the early East Antarctic Ice Sheet grew rapidly and developed a cold-based core that preserved the alpine landscape. The patterns of landscape evolution identified provide the earliest evidence for the development of the East Antarctic Ice Sheet and can be used to test coupled ice-climate evolution models.

  13. Antarctic Tephrochronology: A Maturing Record of Visible Layers and Cryptotephra

    NASA Astrophysics Data System (ADS)

    Dunbar, N. W.; Kurbatov, A.; McIntosh, W. C.

    2012-12-01

    Visible tephra layers, which represent important time-stratigraphic markers in ice-bound climate records, have been found in majority of the deep Antarctic ice cores. Ice core tephra layers range from sub-centimeter thick, visible layers to cryptotephra consisting of sparse, fine-grained (<10 micron) glass particles. Identification of tephra layers traditionally relied on visual identification or acidity spikes association with sulfate aerosols, but is now also aided by fluorescence and downhole optical logging techniques. Improved analytical techniques for glass characterization, and more complete information on source eruptions has allowed development of a regional record of Antarctic volcanic eruptions. Two deep West Antarctic ice cores (Siple Dome SDMA and West Antarctic Ice Sheet Divide core WDC06A) contain rich tephra records, with the former containing 37 tephra layers and the latter containing several hundred distinct, visible "dusty" layers, many of which are likely to be tephra. Based on analyses of all identified tephra layers in the Siple Dome A and B ice cores and of a subset of those in WDC06A, most layers appear to be derived from two large West Antarctic stratovolcanoes Mt. Berlin and Mt. Takahe, tephra from which have also been recognized in the marine record (Hillenbrand et al., 1988). However, a well-defined ash layer recognized at a depth of between 190.37-190.39 m depth in the WDC06A core and several other ice cores, which contains 20 μm ash shards, was chemically characterized as being derived from the East Antarctic Pleiades volcanic center. Several tephra layers, including one that correlates between the SDMA and WDC06A cores, are thought to be related to South American volcanism. In terms of the West Antarctic regional tephra framework, a very distinct "visible brown layer", with glass shards up to 20 μm in diameter, found at a depth of 1586.363 m in WDC06A (8.279 ka B.P. preliminary age), chemically correlates to a major 40Ar/39Ar

  14. Antarctic ozone hole hits record depth

    SciTech Connect

    Not Available

    1991-10-18

    A bad year for the ozone over Antarctica looked like a good bet this year. For the past 2 years, stratospheric ozone destruction has equaled the record set in 1987. Now things look even worse, with a record-setting ozone hole. In 1987, 1989, and 1990, the minimum amount of ozone over Antarctica early each October was 120 to 125 Dobson units compared to the typical level of 220 that prevailed before manmade Chlorofluorocarbons (CFCs) began eating into the ozone layer. The depletion allowed as much as twice the usual amount of biologically damaging ultraviolet light to reach the earth's surface. But researchers took some comfort in the fact that the hole seemed to have hit a barrier to further losses. Now that barrier may have been breached. On 6 October, the satellite-borne Total Ozone Mapping Spectrometer detected an ozone minimum of 110 Dobson units. The region of the lower stratosphere where icy cloud particles and the chlorine of CFCs combine to destroy ozone - between 14 and 24 kilometers - looks much the same as it did in 1987.

  15. Macrofossil records of West Antarctic Ice Sheet retreat during the Holocene

    NASA Technical Reports Server (NTRS)

    Berkman, Paul Arthur

    1993-01-01

    Marine macrofossils in emerged beaches around Antarctica represent a geochemical framework for interpreting meltwater signatures associated with variations in the adjacent ice sheet margins during the last 10,000 years. In particular, mollusc species provide ideal experimental templates for assessing hydrochemical variations in Antarctic coastal marine environments because of their excellent preservation, high abundances, circumpolar distributions, and carbonate shells, which incorporate trace elements and stable isotopes. Modern samples of the bivalve Adamussium colbecki, which were collected across a depth gradient in the vicinity of a glacial meltwater stream in West McMurdo Sound, revealed shell trace element concentrations that were significantly higher above 10 meters because of their exposure to meltwater runoff. This meltwater signature also was reflected by the shell oxygen isotopic composition, which was in equilibrium with the ambient seawater, as demonstrated by the overlap between the predicted and actual O-(delta-18)sub w values. These modern samples provide analogs for interpreting the geochemical records in their fossils, which were based solely on molluscan fossils, complement the above geochemical data by suggesting that the rate of beach emergence fluctuated around Antarctica during the mid-Holocene. Paleoenvironmental analysis of macrofossils from emerged beaches represents a new direction in Antarctic research that can be used to assess changes in the margins of the ice sheets since the Last Glacial Maximum. The resolution of these analyses will be enhanced by collaborations that are developing with scientists who are conducting comparable studies in other coastal regions around the continent.

  16. Prograde Metamorphism recorded in Antarctic Granulite

    NASA Astrophysics Data System (ADS)

    Marschall, H.; Pauly, J.; Chatterjee, N.; Monteleone, B.; Meyer, H. P.

    2015-12-01

    High-grade metamorphic rocks provide an archive of tectonic processes and record conditions in the deep roots of orogenic belts. Granulites typically preserve chemical and mineralogical evidence of the peak temperature to which crustal rocks may be subjected, and they commonly preserve a multitude of textural and chemical features that allow a rather detailed reconstruction of their cooling and exhumation. More rarely, however, is it possible to reconstruct parts of the prograde path, which would allow a reconstruction of the loading and heating of the rocks. Access to the prograde P-T path and the rates and durations involved in granulite formation would provide important constraints on the convergence part of orogenic processes. Here we investigated a sample of felsic granulite from the H.U. Sverdrupfjella, which is part of the high-grade Maud Belt (East Antarctica). Peak-metamorphic conditions of approximately 925 °C and 1.45 GPa persisted for a maximum of circa 14 million years and were attained shortly after 570 Ma. In addition to the short-lived temperature peak, zircon preserved evidence for protracted granulite facies conditions with temperatures above 800 °C persisting for approximately 40 million years. Constraints on prograde metamorphism are recorded by garnet that preserved pre-peak metamorphic growth zones, by Ti zonation in zircon and by rutile inclusions in garnet. Zr-in-rutile thermometry using rutile included in different generations of garnet is used to reconstruct the prograde P-T path documenting burial followed by heating to ultra-high temperatures at peak pressures. Complementary, Ti zonation in prograde cores of zircon grains document and date heating, whereas younger zircon rims show again lower Ti-in-zircon temperatures and date the retrograde stages of metamorphism. The highest T is recorded in rutile, but not in zircon, consistent with the dissolution rather than growth of zircon at ultra-high temperatures. The clockwise loading

  17. Antarctic climate signature in the Greenland ice core record

    PubMed Central

    Barker, Stephen; Knorr, Gregor

    2007-01-01

    A numerical algorithm is applied to the Greenland Ice Sheet Project 2 (GISP2) dust record from Greenland to remove the abrupt changes in dust flux associated with the Dansgaard–Oeschger (D–O) oscillations of the last glacial period. The procedure is based on the assumption that the rapid changes in dust are associated with large-scale changes in atmospheric transport and implies that D–O oscillations (in terms of their atmospheric imprint) are more symmetric in form than can be inferred from Greenland temperature records. After removal of the abrupt shifts the residual, dejumped dust record is found to match Antarctic climate variability with a temporal lag of several hundred years. It is argued that such variability may reflect changes in the source region of Greenland dust (thought to be the deserts of eastern Asia). Other records from this region and more globally also reveal Antarctic-style variability and suggest that this signal is globally pervasive. This provides the potential basis for suggesting a more important role for gradual changes in triggering more abrupt transitions in the climate system. PMID:17954910

  18. Organic and mineral imprints in fossil photosynthetic mats of an East Antarctic lake.

    PubMed

    Lepot, K; Compère, P; Gérard, E; Namsaraev, Z; Verleyen, E; Tavernier, I; Hodgson, D A; Vyverman, W; Gilbert, B; Wilmotte, A; Javaux, E J

    2014-09-01

    Lacustrine microbial mats in Antarctic ice-free oases are considered modern analogues of early microbial ecosystems as their primary production is generally dominated by cyanobacteria, the heterotrophic food chain typically truncated due to extreme environmental conditions, and they are geographically isolated. To better understand early fossilization and mineralization processes in this context, we studied the microstructure and chemistry of organo-mineral associations in a suite of sediments 50-4530 cal. years old from a lake in Skarvsnes, Lützow Holm Bay, East Antarctica. First, we report an exceptional preservation of fossil autotrophs and their biomolecules on millennial timescales. The pigment scytonemin is preserved inside cyanobacterial sheaths. As non-pigmented sheaths are also preserved, scytonemin likely played little role in the preservation of sheath polysaccharides, which have been cross-linked by ether bonds. Coccoids preserved thylakoids and autofluorescence of pigments such as carotenoids. This exceptional preservation of autotrophs in the fossil mats argues for limited biodegradation during and after deposition. Moreover, cell-shaped aggregates preserved sulfur-rich nanoglobules, supporting fossilization of instable intracellular byproducts of chemotrophic or phototrophic S-oxidizers. Second, we report a diversity of micro- to nanostructured CaCO3 precipitates intimately associated with extracellular polymeric substances, cyanobacteria, and/or other prokaryotes. Micro-peloids Type 1 display features that distinguish them from known carbonates crystallized in inorganic conditions: (i) Type 1A are often filled with globular nanocarbonates and/or surrounded by a fibrous fringe, (ii) Type 1B are empty and display ovoid to wrinkled fringes of nanocrystallites that can be radially oriented (fibrous or triangular) or multilayered, and (iii) all show small-size variations. Type 2 rounded carbonates 1-2 μm in diameter occurring inside autofluorescent

  19. Estimating times of extinction in the fossil record.

    PubMed

    Wang, Steve C; Marshall, Charles R

    2016-04-01

    Because the fossil record is incomplete, the last fossil of a taxon is a biased estimate of its true time of extinction. Numerous methods have been developed in the palaeontology literature for estimating the true time of extinction using ages of fossil specimens. These methods, which typically give a confidence interval for estimating the true time of extinction, differ in the assumptions they make and the nature and amount of data they require. We review the literature on such methods and make some recommendations for future directions. PMID:27122005

  20. A Record of Antarctic Climate and Ice Sheet History Recovered

    NASA Astrophysics Data System (ADS)

    Naish, Tim; Powell, Ross; Levy, Richard; Florindo, Fabio; Harwood, David; Kuhn, Gerhard; Niessen, Frank; Talarico, Franco; Wilson, Gary

    2007-12-01

    Antarctica's late Cenozoic (the past ~15 million years) climate history is poorly known from direct evidence, owing to its remoteness, an extensive sea ice apron, and an ice sheet cover over the region for the past 34 million years. Consequently, knowledge about the role of Antarctica's ice sheets in global sea level and climate has relied heavily upon interpretations of oxygen isotope records from deep-sea cores. Whereas these isotopic records have revolutionized our understanding of climate-ice-ocean interactions, questions still remain about the specific role of Antarctic ice sheets in global climate. Such questions can be addressed from geological records at the marine margin of the ice sheets, recovered by drilling from floating ice platforms [e.g., Davey et al., 2001; Harwood et al., 2006; Barrett, 2007].

  1. The 2014 high record of Antarctic sea ice extent

    NASA Astrophysics Data System (ADS)

    Massonnet, Francois; Guemas, Virginie; Fuckar, Neven; Doblas-Reyes, Francisco

    2016-04-01

    In September 2014, Antarctic sea ice extent exceeded the symbolic level of 20 million km²for the first time since 1978, when reliable satellite measurements became available. After the successive records of 2012 and 2013, sea ice extent in 2014 once again reinforced the positive trend observed since the late 1970s. We conduct here a dedicated study to elucidate the origins of a major, and perhaps the most intriguing, event that happened at our Poles recently. Observations, reanalyses and model results all point towards the important role of winds in modifying near-surface heat advection patterns around Antarctica. The role of pre-conditioning (summer conditions) is found to be of lesser importance. Finally, we find no evidence that anomalous freshwater forcing (from atmospheric or continental origin) could have explained the record extent of 2014.

  2. A fossil record of galaxy encounters.

    PubMed

    Elbaz, David; Cesarsky, Catherine J

    2003-04-11

    The cosmic infrared background (CIRB) is a record of a large fraction of the emission of light by stars and galaxies over time. The bulk of this emission has been resolved by the Infrared Space Observatory camera. The dominant contributors are bright starburst galaxies with redshift z approximately 0.8; that is, in the same redshift range as the active galactic nuclei responsible for the bulk of the x-ray background. At the longest wavelengths, sources of redshift z >/= 2 tend to dominate the CIRB. It appears that the majority of present-day stars have been formed in dusty starbursts triggered by galaxy-galaxy interactions and the buildup of large-scale structures. PMID:12690183

  3. Absolute measures of the completeness of the fossil record

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    Measuring the completeness of the fossil record is essential to understanding evolution over long timescales, particularly when comparing evolutionary patterns among biological groups with different preservational properties. Completeness measures have been presented for various groups based on gaps in the stratigraphic ranges of fossil taxa and on hypothetical lineages implied by estimated evolutionary trees. Here we present and compare quantitative, widely applicable absolute measures of completeness at two taxonomic levels for a broader sample of higher taxa of marine animals than has previously been available. We provide an estimate of the probability of genus preservation per stratigraphic interval, and determine the proportion of living families with some fossil record. The two completeness measures use very different data and calculations. The probability of genus preservation depends almost entirely on the Palaeozoic and Mesozoic records, whereas the proportion of living families with a fossil record is influenced largely by Cenozoic data. These measurements are nonetheless highly correlated, with outliers quite explicable, and we find that completeness is rather high for many animal groups.

  4. Evidence for Evolution from the Vertebrate Fossil Record.

    ERIC Educational Resources Information Center

    Gingerich, Philip D.

    1983-01-01

    Discusses three examples of evolutionary transition in the vertebrate fossil record, considering evolutionary transitions at the species level. Uses archaic squirrel-like Paleocine primates, the earliest primates of modern aspect, as examples. Also reviews new evidence on the origin of whales and their transition from land to sea. (JN)

  5. A Maturing Tephra Record in the West Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Dunbar, N. W.; Kurbatov, A.; McIntosh, W. C.

    2011-12-01

    Tephra layers found in many Antarctic ice cores range from sub-centimeter thick, visible layers to cryptotephra consisting of sparse, fine-grained (<10 micron) glass particles. Location of tephra particles has improved with advances in methods of detecting cryptotephra in ice cores. Identification of tephra layers traditionally relied on visible detection or association with sulfate aerosols, but is now supplemented by downhole optical logging (Bay et al., 2001). Improved analytical techniques for glass characterization, such as high quality quantitative electron microprobe analysis, and more complete information on source eruptions has facilitated identification of tephra horizons in ice cores. Two deep ice cores drilled in West Antarctica (Siple Dome and WAIS Divide) contain rich tephra records, with the former containing 37 tephra layers and the latter containing several hundred distinct, visible layers, many of which are likely to be tephra. Most of the tephra layers with strong correlations to sources are derived from Antarctic volcanoes, many from two large West Antarctic stratovolcanoes Mt. Berlin and Mt. Takahe, tephra from which have also been recognized in the marine record (Hillenbrand et al., 1988). A well-defined ash layer is found at a depth of between 190.37-190.39 m depth in the WAIS Divide core, containing 20 um ash shards that are chemically correlated to the the Pleaides volcanoes, in northern Victoria Land. This tephra layer correlates to one found in a Siple Dome (B) ice core (97.2 to 97.7 m depth) and in the Taylor Dome ice core (79.2 m depth). Deeper parts of the WAIS Divide ice core correspond to a time interval of abundant regional volcanism, represented by the large number of visible dust bands and cloudy layers in the core (A. Orsi, pers. comm., 2010). A distinct "visible brown layer" at a depth of 1586.363 m. (8.279 Ky BP preliminary age) is very likely to be from a major eruption of the West Antarctic volcano Mt. Takahe (8.2±5

  6. Giving the early fossil record of sponges a squeeze.

    PubMed

    Antcliffe, Jonathan B; Callow, Richard H T; Brasier, Martin D

    2014-11-01

    Twenty candidate fossils with claim to be the oldest representative of the Phylum Porifera have been re-analysed. Three criteria are used to assess each candidate: (i) the diagnostic criteria needed to categorize sponges in the fossil record; (ii) the presence, or absence, of such diagnostic features in the putative poriferan fossils; and (iii) the age constraints for the candidate fossils. All three criteria are critical to the correct interpretation of any fossil and its placement within an evolutionary context. Our analysis shows that no Precambrian fossil candidate yet satisfies all three of these criteria to be a reliable sponge fossil. The oldest widely accepted candidate, Mongolian silica hexacts from c. 545 million years ago (Ma), are here shown to be cruciform arsenopyrite crystals. The oldest reliable sponge remains are siliceous spicules from the basal Cambrian (Protohertzina anabarica Zone) Soltanieh Formation, Iran, which are described and analysed here in detail for the first time. Extensive archaeocyathan sponge reefs emerge and radiate as late as the middle of the Fortunian Stage of the Cambrian and demonstrate a gradual assembly of their skeletal structure through this time coincident with the evolution of other metazoan groups. Since the Porifera are basal in the Metazoa, their presence within the late Proterozoic has been widely anticipated. Molecular clock calibration for the earliest Porifera and Metazoa should now be based on the Iranian hexactinellid material dated to c. 535 Ma. The earliest convincing fossil sponge remains appeared at around the time of the Precambrian-Cambrian boundary, associated with the great radiation events of that interval. PMID:24779547

  7. Testing New Proxies for Photosymbiosis in the Fossil Record

    NASA Astrophysics Data System (ADS)

    Tornabene, C.; Martindale, R. C.; Schaller, M. F.

    2015-12-01

    Photosymbiosis is a mutualistic relationship that many corals have developed with dinoflagellates called zooxanthellae. The dinoflagellates, of the genus Symbiodinium, photosynthesize and provide corals with most of their energy, while in turn coral hosts live in waters where zooxanthellae have optimal exposure to sunlight. Thanks to this relationship, symbiotic corals calcify faster than non-symbiotic corals. Photosymbiosis is therefore considered the evolutionary innovation that allowed corals to become major reef-builders through geological time.This relationship is extremely difficult to study. Zooxanthellae, which are housed in the coral tissue, are not preserved in fossil coral skeletons, thus determining whether corals had symbionts requires a robust proxy. In order to address this critical question, the goal of this research is to test new proxies for ancient photosymbiosis. Currently the project is focused on assessing the nitrogen (δ15N) isotopes of corals' organic matrices, sensu Muscatine et al. (2005), as well as carbon and oxygen (δ13C, δ18O) isotopes of fossil coral skeletons. Samples from Modern, Pleistocene, Oligocene and Triassic coral skeletons were analyzed to test the validity of these proxies. Coral samples comprise both (interpreted) symbiotic and non-symbiotic fossil corals from the Oligocene and Triassic as well as symbiotic fossil corals from the Modern and Pleistocene to corroborate our findings with the results of Muscatine et al. (2005). Samples were tested for diagenesis through petrographic and scanning electron microscope (SEM) analyses to avoid contamination. Additionally, a novel technique that has not yet been applied to the fossil record was tested. The technique aims to recognize dinosterol, a dinoflagellate biomarker, in both modern and fossil coral samples. The premise of this proxy is that symbiotic corals should contain the dinoflagellate biomarker, whereas those lacking symbionts should lack dinosterol. Results from this

  8. Earth's early fossil record: Why not look for similar fossils on Mars?

    NASA Technical Reports Server (NTRS)

    Awramik, Stanley M.

    1989-01-01

    The oldest evidence of life on Earth is discussed with attention being given to the structure and formation of stromatolites and microfossils. Fossilization of microbes in calcium carbonate or chert media is discussed. In searching for fossil remains on Mars, some lessons learned from the study of Earth's earliest fossil record can be applied. Certain sedimentary rock types and sedimentary rock configurations should be targeted for investigation and returned by the Martian rover and ultimately by human explorers. Domical, columnar to wavy laminated stratiform sedimentary rocks that resemble stromatolites should be actively sought. Limestone, other carbonates, and chert are the favored lithology. Being macroscopic, stromatolites might be recognized by an intelligent unmanned rover. In addition, black, waxy chert with conchoidal fracture should be sought. Chert is by far the preferred lithology for the preservation of microbes and chemical fossils. Even under optimal geological conditions (little or no metamorphism or tectonic alteration, excellent outcrops, and good black chert) and using experienced field biogeologists, the chances of finding well preserved microbial remains in chert are very low.

  9. Diversity dynamics: molecular phylogenies need the fossil record.

    PubMed

    Quental, Tiago B; Marshall, Charles R

    2010-08-01

    Over the last two decades, new tools in the analysis of molecular phylogenies have enabled study of the diversification dynamics of living clades in the absence of information about extinct lineages. However, computer simulations and the fossil record show that the inability to access extinct lineages severely limits the inferences that can be drawn from molecular phylogenies. It appears that molecular phylogenies can tell us only when there have been changes in diversification rates, but are blind to the true diversity trajectories and rates of origination and extinction that have led to the species that are alive today. We need to embrace the fossil record if we want to fully understand the diversity dynamics of the living biota. PMID:20646780

  10. Exopaleontology and the search for a fossil record on Mars

    NASA Technical Reports Server (NTRS)

    Farmer, Jack D.; Desmarais, D. J.

    1994-01-01

    Although present Martian surface conditions appear unfavorable for life as we know it, there is compelling geological evidence that the climate of early Mars was much more Earth-like, with a denser atmosphere and abundant surface water. The fact that life developed on the Earth within the first billion years of its history makes it quite plausible that life may have also developed on Mars. If life did develop on Mars, it is likely to have left behind a fossil record. This has led to the development of a new subdiscipline of paleontology, herein termed 'exopaleontology', which deals with the exploration for fossils on other planets. The most important factor enhancing microbial fossilization is the rapid entombment of microorganisms by fine-grained, stable mineral phases, such as silica, phosphate, or carbonate. The oldest body fossils on Earth are preserved in this way, occurring as permineralized cells in fine-grained siliceous sediments (cherts) associated with ancient volcanic terranes in Australia and South Africa. Modern terrestrial environments where minerals may precipitate in the presence of microorganisms include subaerial thermal springs and shallow hydrothermal systems, sub-lacustrine springs and evaporitic alkaline lakes, zones of mineralization within soils where 'hardpans' (e.g. calcretes, silcretes) form, and high latitude frozen soils or ground ice.

  11. First record of Podocarpoid fossil wood in South China

    PubMed Central

    Li, Long; Jin, Jian-Hua; Quan, Cheng; Oskolski, Alexei A.

    2016-01-01

    A new species of fossil conifer wood, Podocarpoxylon donghuaiense sp. nov., is described from the late Eocene of Nadu Formation in Baise Basin of the Guangxi Province, South China. This fossil wood is characterized by distinct growth rings, circular to oval tracheids in cross section, 1–2-seriate opposite pits on radial tracheid walls, uniseriate (rarely biseriate) rays, smooth end walls of ray parenchyma cells, and the absence of resin ducts, suggesting its affinity to Podocarpaceae. The new species is distinctive from other Cenozoic woods ascribed to this family by the combination of distinctive growth rings, the absence of axial parenchyma, the occurrence of bordered pits on tangential tracheid walls, and the occurrence of 3–4 cuppressoid or taxodioid pits on cross-fields. This represents the first record of podocarpoid fossil wood in South China and provides fossil evidence for the early dispersal and diversification of Podocarpaceae in eastern Asia as well as for mild temperate seasonal climate in this region during the late Eocene. PMID:27571780

  12. First record of Podocarpoid fossil wood in South China.

    PubMed

    Li, Long; Jin, Jian-Hua; Quan, Cheng; Oskolski, Alexei A

    2016-01-01

    A new species of fossil conifer wood, Podocarpoxylon donghuaiense sp. nov., is described from the late Eocene of Nadu Formation in Baise Basin of the Guangxi Province, South China. This fossil wood is characterized by distinct growth rings, circular to oval tracheids in cross section, 1-2-seriate opposite pits on radial tracheid walls, uniseriate (rarely biseriate) rays, smooth end walls of ray parenchyma cells, and the absence of resin ducts, suggesting its affinity to Podocarpaceae. The new species is distinctive from other Cenozoic woods ascribed to this family by the combination of distinctive growth rings, the absence of axial parenchyma, the occurrence of bordered pits on tangential tracheid walls, and the occurrence of 3-4 cuppressoid or taxodioid pits on cross-fields. This represents the first record of podocarpoid fossil wood in South China and provides fossil evidence for the early dispersal and diversification of Podocarpaceae in eastern Asia as well as for mild temperate seasonal climate in this region during the late Eocene. PMID:27571780

  13. An overview of the dinosaur fossil record from Chile

    NASA Astrophysics Data System (ADS)

    Rubilar-Rogers, David; Otero, Rodrigo A.; Yury-Yáñez, Roberto E.; Vargas, Alexander O.; Gutstein, Carolina S.

    2012-08-01

    In Chile, the record of dinosaurs in Jurassic and Cretaceous sediments is often restricted to footprints, with few skeletal remains. Tetanuran theropods are known in the Upper Jurassic, and bones of titanosaur sauropods in the Late Cretaceous, including partial skeletons (e.g. Atacamatitan chilensis Kellner et al.). Also from the late Cretaceous, an ornithopod vertebra, a pair of theropod teeth and one tarsometatarsus of a gaviiform bird (Neogaeornis wetzeli Lambrecht) have been reported. The Cenozoic fossil record comprises abundant and well-preserved marine birds from Eocene and Miocene units, with a specially abundant record of Sphenisciformes and less frequently, Procellariiformes. There is an excellent Miocene-Pliocene record of other birds such as Odontopterygiformes, including the most complete skeleton ever found of a pelagornithid, Pelagornis chilensis Mayr and Rubilar-Rogers. Fossil birds are also known from Pliocene and Pleistocene strata. A remarkable collection of birds was discovered in lacustrine sediments of late Pleistocene age associated to human activity. The perspectives in the study of dinosaurs in Chile are promising because plenty of material stored in institutional collections is not described yet. The record of Chilean dinosaurs is relevant for understanding the dynamics and evolution of this group of terrestrial animals in the western edge of Gondwana, while Cenozoic birds from the Region may contribute to the understanding of current biogeography for instance, the effect of the emergence and establishment of the Humboldt Current.

  14. The fossil record and macroevolutionary history of the beetles.

    PubMed

    Smith, Dena M; Marcot, Jonathan D

    2015-04-22

    Coleoptera (beetles) is the most species-rich metazoan order, with approximately 380 000 species. To understand how they came to be such a diverse group, we compile a database of global fossil beetle occurrences to study their macroevolutionary history. Our database includes 5553 beetle occurrences from 221 fossil localities. Amber and lacustrine deposits preserve most of the beetle diversity and abundance. All four extant suborders are found in the fossil record, with 69% of all beetle families and 63% of extant beetle families preserved. Considerable focus has been placed on beetle diversification overall, however, for much of their evolutionary history it is the clade Polyphaga that is most responsible for their taxonomic richness. Polyphaga had an increase in diversification rate in the Early Cretaceous, but instead of being due to the radiation of the angiosperms, this was probably due to the first occurrences of beetle-bearing amber deposits in the record. Perhaps, most significant is that polyphagan beetles had a family-level extinction rate of zero for most of their evolutionary history, including across the Cretaceous-Palaeogene boundary. Therefore, focusing on the factors that have inhibited beetle extinction, as opposed to solely studying mechanisms that may promote speciation, should be examined as important determinants of their great diversity today. PMID:25788597

  15. The fossil record and macroevolutionary history of the beetles

    PubMed Central

    Smith, Dena M.; Marcot, Jonathan D.

    2015-01-01

    Coleoptera (beetles) is the most species-rich metazoan order, with approximately 380 000 species. To understand how they came to be such a diverse group, we compile a database of global fossil beetle occurrences to study their macroevolutionary history. Our database includes 5553 beetle occurrences from 221 fossil localities. Amber and lacustrine deposits preserve most of the beetle diversity and abundance. All four extant suborders are found in the fossil record, with 69% of all beetle families and 63% of extant beetle families preserved. Considerable focus has been placed on beetle diversification overall, however, for much of their evolutionary history it is the clade Polyphaga that is most responsible for their taxonomic richness. Polyphaga had an increase in diversification rate in the Early Cretaceous, but instead of being due to the radiation of the angiosperms, this was probably due to the first occurrences of beetle-bearing amber deposits in the record. Perhaps, most significant is that polyphagan beetles had a family-level extinction rate of zero for most of their evolutionary history, including across the Cretaceous–Palaeogene boundary. Therefore, focusing on the factors that have inhibited beetle extinction, as opposed to solely studying mechanisms that may promote speciation, should be examined as important determinants of their great diversity today. PMID:25788597

  16. The hominin fossil record: taxa, grades and clades

    PubMed Central

    Wood, Bernard; Lonergan, Nicholas

    2008-01-01

    This paper begins by reviewing the fossil evidence for human evolution. It presents summaries of each of the taxa recognized in a relatively speciose hominin taxonomy. These taxa are grouped in grades, namely possible and probable hominins, archaic hominins, megadont archaic hominins, transitional hominins, pre-modern Homo and anatomically modern Homo. The second part of this contribution considers some of the controversies that surround hominin taxonomy and systematics. The first is the vexed question of how you tell an early hominin from an early panin, or from taxa belonging to an extinct clade closely related to the Pan-Homo clade. Secondly, we consider how many species should be recognized within the hominin fossil record, and review the philosophies and methods used to identify taxa within the hominin fossil record. Thirdly, we examine how relationships within the hominin clade are investigated, including descriptions of the methods used to break down an integrated structure into tractable analytical units, and then how cladograms are generated and compared. We then review the internal structure of the hominin clade, including the problem of how many subclades should be recognized within the hominin clade, and we examine the reliability of hominin cladistic hypotheses. The last part of the paper reviews the concepts of a genus, including the criteria that should be used for recognizing genera within the hominin clade. PMID:18380861

  17. Maturation experiments reveal bias in the fossil record of feathers

    NASA Astrophysics Data System (ADS)

    McNamara, Maria; Field, Daniel

    2016-04-01

    The evolutionary history of birds and feathers is a major focus in palaeobiology and evolutionary biology. Diverse exceptionally preserved birds and feathered dinosaurs from Jurassic and Cretaceous biotas in China have provided pivotal evidence of early feathers and feather-like integumentary features, but the true nature of many of these fossil soft tissues is still debated. Interpretations of feathers at intermediate developmental stages (i.e. Stages II, III and IV) and of simple quill-like (Stage I) feathers are particularly controversial. This reflects key uncertainties relating to the preservation potential of feathers at different evolutionary-developmental stages, and to the relative preservation potential of diagnostic features of Stage I feathers and hair. To resolve these issues, we used high pressure-high temperature autoclave experiments to simulate the effects of burial on modern feathers from the Black Coucal (Centropus grilii) and Common Starling (Sturnus vulgaris), and on human hair. Our results reveal profound differences in the recalcitrance of feathers of different types during maturation: Stage I and Stage V feathers retain diagnostic morphological and ultrastructural details following maturation, whereas other feather types do not. Further, the morphology and arrangement of certain ultrastructural features diagnostic of Stages III and IV, e.g. barbules, are preferentially lost during maturation. These results indicate a pervasive bias in the fossil record of feathers, whereby preservation of feathers at Stages I and V is favored. Critical stages in the evolution of feathers, i.e. Stages II, III and IV, are less likely to be preserved and more likely to be misinterpreted as feathers at earlier developmental stages. Our discovery has major implications for our understanding of the fidelity of the fossil record of feathers and provides a framework for testing the significance of putative examples of fossil feathers at different developmental

  18. Disentangling rock record bias and common-cause from redundancy in the British fossil record.

    PubMed

    Dunhill, Alexander M; Hannisdal, Bjarte; Benton, Michael J

    2014-01-01

    The fossil record documents the history of life, but the reliability of that record has often been questioned. Spatiotemporal variability in sedimentary rock volume, sampling and research effort especially frustrates global-scale diversity reconstructions. Various proposals have been made to rectify palaeodiversity estimates using proxy measures for the availability and sampling of the rock record, but the validity of these approaches remains controversial. Targeting the rich fossil record of Great Britain as a highly detailed regional exemplar, our statistical analysis shows that marine outcrop area contains a signal useful for predicting changes in diversity, collections and formations, whereas terrestrial outcrop area contains a signal useful for predicting formations. In contrast, collection and formation counts are information redundant with fossil richness, characterized by symmetric, bidirectional information flow. If this is true, the widespread use of collection and formation counts as sampling proxies to correct the raw palaeodiversity data may be unwarranted. PMID:25187994

  19. At the origin of animals: the revolutionary cambrian fossil record.

    PubMed

    Budd, Graham E

    2013-09-01

    The certain fossil record of animals begins around 540 million years ago, close to the base of the Cambrian Period. A series of extraordinary discoveries starting over 100 years ago with Walcott's discovery of the Burgess Shale has accelerated in the last thirty years or so with the description of exceptionally-preserved Cambrian fossils from around the world. Such deposits of "Burgess Shale Type" have been recently complemented by other types of exceptional preservation. Together with a remarkable growth in knowledge about the environments that these early animals lived in, these discoveries have long exerted a fascination and strong influence on views on the origins of animals, and indeed, the nature of evolution itself. Attention is now shifting to the period of time just before animals become common, at the base of the Cambrian and in the preceding Ediacaran Period. Remarkable though the Burgess Shale deposits have been, a substantial gap still exists in our knowledge of the earliest animals. Nevertheless, the fossils from this most remarkable period of evolutionary history continue to exert a strong influence on many aspects of animal evolution, not least recent theories about developmental evolution. PMID:24396267

  20. At the Origin of Animals: The Revolutionary Cambrian Fossil Record

    PubMed Central

    Budd, Graham E

    2013-01-01

    The certain fossil record of animals begins around 540 million years ago, close to the base of the Cambrian Period. A series of extraordinary discoveries starting over 100 years ago with Walcott’s discovery of the Burgess Shale has accelerated in the last thirty years or so with the description of exceptionally-preserved Cambrian fossils from around the world. Such deposits of “Burgess Shale Type” have been recently complemented by other types of exceptional preservation. Together with a remarkable growth in knowledge about the environments that these early animals lived in, these discoveries have long exerted a fascination and strong influence on views on the origins of animals, and indeed, the nature of evolution itself. Attention is now shifting to the period of time just before animals become common, at the base of the Cambrian and in the preceding Ediacaran Period. Remarkable though the Burgess Shale deposits have been, a substantial gap still exists in our knowledge of the earliest animals. Nevertheless, the fossils from this most remarkable period of evolutionary history continue to exert a strong influence on many aspects of animal evolution, not least recent theories about developmental evolution. PMID:24396267

  1. Aragonite and the fossil record: are we overlooking something?

    NASA Astrophysics Data System (ADS)

    Balthasar, Uwe

    2016-04-01

    Aragonite and calcite are the two most common minerals from which marine organisms secrete their skeletons, yet their potential to preserve in the fossil record is very different. While calcite is generally very stable, aragonite dissolves relatively easily either during diagenesis or even pre-burial. While the complete loss of aragonitic shells is generally acknowledged, the original contribution of aragonite to commonly preserved calcareous fossils is generally overlooked, particularly in groups with no recent representatives. Palaeozoic brachiopods and stromatoporoid sponges, for example, are traditionally considered to have been made of calcite. However, EBSD work on stromatoporoids shows a complex early diagenesis during which the skeletal walls recrystallised first and served as the nucleation surface for the cements infilling the open galleries between the walls. This suggests that the original mineral composition of the skeletal walls had a high diagenetic potential which makes a stable low-magnesium calcite composition unlikely. Equally, the biggest subphylum of brachiopods, Rhynchonelliformea, is traditionally considered to have shells that are exclusively made of low-magnesium calcite. However, a survey of the shell thickness of 176 Ordovician-Silurian brachiopod valves reveals that the calcitic remains of some of the larger shells (particularly of pentamerids) are far too thin with several specimens exhibiting the irregular internal margins typical of dissolution, thus suggesting a bimineralic composition with an outer calcite and an inner aragonite layer. These examples indicate that existing estimates of Phanerozoic aragonite and calcite skeletal mineralogy are not only biased by the complete dissolution of shells, but we probably overestimate the abundance of original calcite composition in the fossil record.

  2. Delayed biological recovery from extinctions throughout the fossil record.

    PubMed

    Kirchner, J W; Weil, A

    2000-03-01

    How quickly does biodiversity rebound after extinctions? Palaeobiologists have examined the temporal, taxonomic and geographic patterns of recovery following individual mass extinctions in detail, but have not analysed recoveries from extinctions throughout the fossil record as a whole. Here, we measure how fast biodiversity rebounds after extinctions in general, rather than after individual mass extinctions, by calculating the cross-correlation between extinction and origination rates across the entire Phanerozoic marine fossil record. Our results show that extinction rates are not significantly correlated with contemporaneous origination rates, but instead are correlated with origination rates roughly 10 million years later. This lagged correlation persists when we remove the 'Big Five' major mass extinctions, indicating that recovery times following mass extinctions and background extinctions are similar. Our results suggest that there are intrinsic limits to how quickly global biodiversity can recover after extinction events, regardless of their magnitude. They also imply that today's anthropogenic extinctions will diminish biodiversity for millions of years to come. PMID:10724168

  3. Patterns of generic extinction in the fossil record

    NASA Technical Reports Server (NTRS)

    Raup, D. M.; Boyajian, G. E.

    1988-01-01

    Analysis of the stratigraphic records of 19,897 fossil genera indicates that most classes and orders show largely congruent rises and falls in extinction intensity throughout the Phanerozoic. Even an ecologically homogeneous sample of reef genera shows the same basic extinction profile. The most likely explanation for the congruence is that extinction is physically rather than biologically driven and that it is dominated by the effects of geographically widespread environmental perturbations influencing most habitats. Significant departures from the congruence are uncommon but important because they indicate physiological or habitat selectivity. The similarity of the extinction records of reef organisms and the marine biota as a whole confirms that reefs and other faunas are responding to the same history of environmental stress.

  4. 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

  5. Evolutionary speed limits inferred from the fossil record.

    PubMed

    Kirchner, James W

    2002-01-01

    The dynamics of extinction and diversification determine the long-term effects of extinction episodes. If rapid bursts of extinction are offset by equally rapid bursts of diversification, their biodiversity consequences will be transient. But if diversification rates cannot accelerate rapidly enough, pulses of extinction will lead to long-lasting depletion of biodiversity. Here I use spectral analysis of the fossil record to test whether diversification rates can accelerate as much as extinction rates, over both short and long spans of geological time. I show that although the long-wavelength variability of diversification rates equals or exceeds that of extinctions, diversification rates are markedly less variable than extinction rates at wavelengths shorter than roughly 25 million years. This implies that there are intrinsic speed limits that constrain how rapidly diversification rates can accelerate in response to pulses of extinction. PMID:11780116

  6. 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.

  7. Extinction, diversity and survivorship of taxa in the fossil record

    PubMed Central

    Newman, M. E. J.; Sibani, P.

    1999-01-01

    Using data drawn from large-scale databases, a number of interesting trends in the fossil record have been observed in recent years. These include the average decline in extinction rates throughout the Phanerozoic, the average increase in standing diversity, correlations between rates of origination and extinction, and simple laws governing the form of survivorship curves and the distribution of the lifetimes of taxa. In this paper we derive a number of mathematical relationships between these quantities and show how these different trends are interrelated. We also derive a variety of constraints on the possible forms of these trends, such as limits on the rate at which extinction may decline and limits on the allowed difference between extinction and origination rates at any given time.

  8. Cyclicity in the fossil record mirrors rock outcrop area

    PubMed Central

    Smith, Andrew B; McGowan, Alistair J

    2005-01-01

    In a recent article, Rohde & Muller (Rohde & Muller 2005 Nature 434, 208–210) identified a strong 62 Myr cyclicity in the history of marine diversity through the Phanerozoic. The data they presented were highly convincing, yet they were unable to explain what process might have generated this pattern. A significant correlation between observed genus-level diversity (after removal of long-term trends) and the amount of marine sedimentary rock measured at a surface outcrop in Western Europe is demonstrated. This suggests that cyclicity originates from long-term changes in sedimentary depositional and erosional regimes, and raises the strong possibility that the cyclicity apparent in the record of marine fossils is not a biological signal but a sampling signal. PMID:17148228

  9. Antarctic Crabs: Invasion or Endurance?

    PubMed Central

    Griffiths, Huw J.; Whittle, Rowan J.; Roberts, Stephen J.; Belchier, Mark; Linse, Katrin

    2013-01-01

    Recent scientific interest following the “discovery” of lithodid crabs around Antarctica has centred on a hypothesis that these crabs might be poised to invade the Antarctic shelf if the recent warming trend continues, potentially decimating its native fauna. This “invasion hypothesis” suggests that decapod crabs were driven out of Antarctica 40–15 million years ago and are only now returning as “warm” enough habitats become available. The hypothesis is based on a geographically and spatially poor fossil record of a different group of crabs (Brachyura), and examination of relatively few Recent lithodid samples from the Antarctic slope. In this paper, we examine the existing lithodid fossil record and present the distribution and biogeographic patterns derived from over 16,000 records of Recent Southern Hemisphere crabs and lobsters. Globally, the lithodid fossil record consists of only two known specimens, neither of which comes from the Antarctic. Recent records show that 22 species of crabs and lobsters have been reported from the Southern Ocean, with 12 species found south of 60°S. All are restricted to waters warmer than 0°C, with their Antarctic distribution limited to the areas of seafloor dominated by Circumpolar Deep Water (CDW). Currently, CDW extends further and shallower onto the West Antarctic shelf than the known distribution ranges of most lithodid species examined. Geological evidence suggests that West Antarctic shelf could have been available for colonisation during the last 9,000 years. Distribution patterns, species richness, and levels of endemism all suggest that, rather than becoming extinct and recently re-invading from outside Antarctica, the lithodid crabs have likely persisted, and even radiated, on or near to Antarctic slope. We conclude there is no evidence for a modern-day “crab invasion”. We recommend a repeated targeted lithodid sampling program along the West Antarctic shelf to fully test the validity of the

  10. Spatial and temporal characteristics of the Little Ice Age: The Antarctic ice-core record

    SciTech Connect

    Mosley-Thompson, E.; Thompson, L.G.

    1992-03-01

    Recently, ice core records from both hemispheres, in conjunction with other proxy records (e.g., tree rings, speleothems and corals), have shown that the Little Ice Age (LIA) was spatially extensive, extending to the Antarctic. This paper examines the temporal and spatial characteristics of the dust and delta 18O information from Antarctic ice cores. Substantial differences exist in the records. For example, a 550-year record of delta 18O and dust concentrations from Siple Station, Antarctica suggests that, less dusty conditions prevailed from A.D. 1600 to 1830. Alternately, dust and delta 18O data from South Pole Station indicate that opposite conditions (e.g., cooler and more dusty) were prevalent during the LIA. Three additional Antarctic delta 18O records are integrated with the Siple and South Pole histories for a more comprehensive picture of LIA conditions. The records provide additional support for the LIA temperature opposition between the Antarctic Peninsula region and East Antarctica. In addition, periods of strongest LIA cooling are not temporally synchronous over East Antarctica. These strong regional differences demonstrate that a suite of spatially distributed, high resolution ice core records will be necessary to characterize the LIA in Antarctica.

  11. First record of Babesia sp. in Antarctic penguins.

    PubMed

    Montero, Estrella; González, Luis Miguel; Chaparro, Alberto; Benzal, Jesús; Bertellotti, Marcelo; Masero, José A; Colominas-Ciuró, Roger; Vidal, Virginia; Barbosa, Andrés

    2016-04-01

    This is the first reported case of Babesia sp. in Antarctic penguins, specifically a population of Chinstrap penguins (Pygoscelis antarctica) in the Vapour Col penguin rookery in Deception Island, South Shetlands, Antarctica. We collected peripheral blood from 50 adult and 30 chick Chinstrap penguins. Examination of the samples by microscopy showed intraerythrocytic forms morphologically similar to other avian Babesia species in 12 Chinstrap penguin adults and seven chicks. The estimated parasitaemias ranged from 0.25×10(-2)% to 0.75×10(-2)%. Despite the low number of parasites found in blood smears, semi-nested PCR assays yielded a 274 bp fragment in 12 of the 19 positive blood samples found by microscopy. Sequencing revealed that the fragment was 97% similar to Babesia sp. 18S rRNA from Australian Little Penguins (Eudyptula minor) confirming presence of the parasite. Parasite prevalence estimated by microscopy in adults and chicks was higher (24% vs. 23.3%, respectively) than found by semi-nested PCR (16% vs. 13.3% respectively). Although sampled penguins were apparently healthy, the effect of Babesia infection in these penguins is unknown. The identification of Babesia sp. in Antarctic penguins is an important finding. Ixodes uriae, as the only tick species present in the Antarctic Peninsula, is the key to understanding the natural history of this parasite. Future work should address the transmission dynamics and pathogenicity of Babesia sp. in Chinstrap penguin as well as in other penguin species, such as Gentoo penguin (Pygoscelis papua) and Adélie penguin (Pygoscelis adeliae), present within the tick distribution range in the Antarctic Peninsula. PMID:26874670

  12. NGST: Exploring the Fossil Record of Galaxy Formation

    NASA Technical Reports Server (NTRS)

    Rich, R. Michael

    1998-01-01

    During this grant period the investigator has accomplished the following: developed and researched the science case for high resolution optical imaging with NGST (Next Generation Space Telescope); presented to the ASWG (Ad-Hoc Science Working Group) on the use of NGST to image and measure the proper motions of white dwarf stars that could account for the MACHO events toward the LMC (Large Magellanic Cloud); wrote proposals for the Design Reference Mission. Three proposals have been written on the following topics: Measuring the faint end of the white dwarf luminosity function to get an independent measure of the age of the oldest stars, measurement of the stellar luminosity function over the full range of age, abundance, and population type, and deep imaging of Local Group halos to measure the relative ages of the oldest stars in the Milky Way and other galaxies; he has introduced simulations of crowded field stellar photometry on a hypothetical population in the M31 halo. Using a physically correct luminosity function and a surface brightness of 24.5 mag/sq. arcsec, NGST imaging in 10 hours easily measures the turnoff and reaches 3 mags down the main sequence in the halo of M31; and has delivered talks at the NGST workshop in Liege, and at the meeting in Paris entitled "Connecting the Distant Universe with the Local Fossil Record".

  13. 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

  14. Contributions of Sediment Provenance and Sediment Diagenesis to Western Antarctic Peninsula Magnetic Proxy Records

    NASA Astrophysics Data System (ADS)

    Brachfeld, S.; Manley, P.; Gorring, M.; Ryan, P.

    2007-05-01

    We examine the role of sediment provenance, iron-sulfur diagenesis, and iron-silica diagenesis in shaping environmental magnetic proxy records in Antarctic biosiliceous sediments. A 20-m sediment core from the Gerlache Drift, western Antarctic Peninsula, contains an ultra-high resolution record of environmental change spanning the last 4000 years. Magnetic susceptibility and several remanence parameters appear to record regularly repeating patterns in biogenic and terrigenous sedimentation, with a major shift at the Middle Holocene to Late Holocene transition. This shift is manifested as an abrupt downcore decrease in magnetic susceptibility, concomitant with an increase in biogenic silica. However, this record does not show the typical pattern associated with iron-sulfur diagenesis, i.e., selective dissolution of fine particles and coarsening of the residual assemblage. We observe multidomain magnetite above the transition, and PSD-magnetite plus hematite below the transition, which suggests a change in sediment provenance. However, we observe a change in clay mineralogy downcore that is consistent with predictions for iron-silica diagenesis. In order to investigate the role of changing sediment sources vs. post-depositional diagenesis, we have examined bulk sediment geochemistry, total organic carbon and total sulfur content to identify possible diagenetic fronts, and bulk mineralogic assemblages and lithic clast composition to examine sediment sources. In addition, we have examined the lithologic and geochemical characteristics of surface sediment samples and diamict samples from a North- South suite of western AP fjords and inner shelf basins, which we use to fingerprint potential sediment source regions. These tools may be able to distinguish between sediment supplied from local Antarctic Peninsula geologic terranes, Bransfield Basin volcanics entrained in the nearshore countercurrent, or West Antarctic sediment supplied by the Antarctic Circumpolar Current.

  15. 'Citizen science' recording of fossils by adapting existing computer-based biodiversity recording tools

    NASA Astrophysics Data System (ADS)

    McGowan, Alistair

    2014-05-01

    Biodiversity recording activities have been greatly enhanced by the emergence of online schemes and smartphone applications for recording and sharing data about a wide variety of flora and fauna. As a palaeobiologist, one of the areas of research I have been heavily involved in is the question of whether the amount of rock available to sample acts as a bias on our estimates of biodiversity through time. Although great progress has been made on this question over the past ten years by a number of researchers, I still think palaeontology has not followed the lead offered by the 'citizen science' revolution in studies of extant biodiversity. By constructing clearly structured surveys with online data collection support, it should be possible to collect field data on the occurrence of fossils at the scale of individual exposures, which are needed to test competing hypotheses about these effects at relatively small spatial scales. Such data collection would be hard to justify for universities and museums with limited personnel but a co-ordinated citizen science programme would be capable of delivering such a programme. Data collection could be based on the MacKinnon's Lists method, used in rapid conservation assessment work. It relies on observers collecting lists of a fixed length (e.g. 10 species long) but what is important is that it focuses on getting observers to ignore sightings of the same species until that list is complete. This overcomes the problem of 'common taxa being commonly recorded' and encourages observers to seek out and identify the rarer taxa. This gives a targeted but finite task. Rather than removing fossils, participants would be encouraged to take photographs to share via a recording website. The success of iSpot, which allows users to upload photos of plants and animals for other users to help with identifications, offers a model for overcoming the problems of identifying fossils, which can often look nothing like the examples illustrated in

  16. New Palaeogene horntail wasps (Hymenoptera, Siricidae) and a discussion of their fossil record.

    PubMed

    Wedmann, Sonja; Pouillon, Jean-Marc; Nel, André

    2014-01-01

    The phylogenetic placement of siricid hymenopterans and especially the relationships among Siricidae are not resolved, and are in need of further investigation. The fossil record helps to illuminate the evolutionary history of this group. In this paper, Xoanon? eocenicus sp. nov. is newly described from the Eocene Fossillagerstätte Grube Messel (Germany). Although several characters of the wing venation of this fossil are similar to the extant genus Xoanon, there remain some doubts concerning the generic placement. A newly found fossil is attributed to Urocerus ligniticus (Piton, 1940) from the Paloecene Fossillagerstätte Menat (France) and provides more morphological information on this species. An overview of the fossil record of Siricidae in the strict sense is given and the state of knowledge on the different fossils is reviewed. PMID:25283896

  17. Sea level pressure variability in the Amundsen Sea region inferred from a West Antarctic glaciochemical record

    NASA Astrophysics Data System (ADS)

    Kreutz, K. J.; Mayewski, P. A.; Pittalwala, I. I.; Meeker, L. D.; Twickler, M. S.; Whitlow, S. I.

    2000-02-01

    Using European Center for Medium-Range Weather Forecasts (ECMWF) numerical operational analyses, sea ice extent records, and station pressure data, we investigate the influence of sea level pressure variability in the Amundsen Sea region on a West Antarctic (Siple Dome) glaciochemical record. Empirical orthogonal function analysis of the high-resolution Siple Dome multivariate ice core chemical time series record (SDEOF1) documents lower tropospheric transport of sea-salt aerosols to the site. During 1985-1994 the SDEOF1 record of high (low) aerosol transport corresponds to anomalously low (high) sea level pressure (SLP) in the Amundsen Sea region. Spatial correlation patterns between ECMWF monthly SLP fields and the annual SDEOF1 record suggest that a majority of sea-salt aerosol is transported to Siple Dome during spring (September, October, and November). Analysis of zonal and meridional wind fields supports the SLP/SDEOF1 correlation and suggests the SDEOF1 record is sensitive to changes in regional circulation strength. No relationship is found between sea ice extent and the SDEOF1 record for the period 1973-1994. To investigate the SDEOF1 record prior to ECMWF coverage, a spring transpolar index (STPI) is created, using normalized SLP records from the New Zealand and South America/Antarctic Peninsula sectors, and is significantly correlated (at least 95% c.l.) with the SDEOF1 record on an annual (r = 0.32, p < 0.001) and interannual (3 years; r = 0.51, p < 0.001) basis. Dominant periodicities (3.3 and 7.1 years) in the annual SDEOF1 record (1890-1994 A.D.) suggest that a portion of the recorded interannual variability may be related tropical/extratropical ENSO teleconnections. Changes in the periodic structure of the full (850-1994 A.D.) Siple Dome record suggests a shift in SLP forcing during the Little Ice Age (˜1400-1900 A.D.) interval.

  18. Evidence for an early Holocene climate optimum in the Antarctic deep ice-core record

    SciTech Connect

    Ciais, P.; Lipenkov, V.; Nicolaiev, V.

    1992-01-01

    In the interpretation of the Antarctic deep ice-core data, little attention has been given to the Holocene part of the records. As far as translation of the stable isotope content in terms of temperature is concerned, this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no {sup 14}C dating has yet been available for this type of sequence. In this article, we focus on the Dome C and Vostok cores and on a new 850-m long ice core drilled out at Komsomolskaia by the Soviet Antarctic Expeditions. These three sites are located in East Antarctica, on the Antarctic plateau, in a region essentially undisturbed by ice-flow conditions, so that their detailed intercomparison may allow us to identify the climatically significant isotopic signal. Our results compare well with the proximal records of Southern Hemisphere high latitudes and support the existence of a warmer {open_quotes}climatic optimum{close_quotes} between 10 and 6 ka y BP. Maximum temperatures are reached just at the end of the last deglaciation, which confirms previous observations at high latitudes, in contrast with later dates for the Atlantic and hypsithermal optima in Europe and North America. 60 refs., 6 figs.

  19. Contemporaneous Trace and Body Fossils from a Late Pleistocene Lakebed in Victoria, Australia, Allow Assessment of Bias in the Fossil Record

    PubMed Central

    Camens, Aaron Bruce; Carey, Stephen Paul

    2013-01-01

    The co-occurrence of vertebrate trace and body fossils within a single geological formation is rare and the probability of these parallel records being contemporaneous (i.e. on or near the same bedding plane) is extremely low. We report here a late Pleistocene locality from the Victorian Volcanic Plains in south-eastern Australia in which demonstrably contemporaneous, but independently accumulated vertebrate trace and body fossils occur. Bite marks from a variety of taxa are also present on the bones. This site provides a unique opportunity to examine the biases of these divergent fossil records (skeletal, footprints and bite marks) that sampled a single fauna. The skeletal record produced the most complete fauna, with the footprint record indicating a markedly different faunal composition with less diversity and the feeding traces suggesting the presence, amongst others, of a predator not represented by either the skeletal or footprint records. We found that the large extinct marsupial predator Thylacoleo was the only taxon apparently represented by all three records, suggesting that the behavioral characteristics of large carnivores may increase the likelihood of their presence being detected within a fossil fauna. In contrast, Diprotodon (the largest-ever marsupial) was represented only by trace fossils at this site and was absent from the site's skeletal record, despite its being a common and easily detected presence in late Pleistocene skeletal fossil faunas elsewhere in Australia. Small mammals absent from the footprint record for the site were represented by skeletal fossils and bite marks on bones. PMID:23301008

  20. Gaps in the Rock and Fossil Records and Implications for the Rate and Mode of Evolution.

    ERIC Educational Resources Information Center

    Smith, Grant Sackett

    1988-01-01

    Examines three types of gaps in the fossil record: real gaps, imaginary gaps, and temporary gaps. Reviews some recent evidence concerning evolution from the paleontological record of microfossils, invertebrates, and vertebrates in order to make some general conclusions regarding the manner in which life evolved on earth. (CW)

  1. Integrating developmental biology and the fossil record of reptiles.

    PubMed

    Skawiński, Tomasz; Tałanda, Mateusz

    2014-01-01

    Numerous new discoveries and new research techniques have influenced our understanding of reptile development from a palaeontological perspective. They suggest for example that transition from mineralized to leathery eggshells and from oviparity to viviparity appeared much more often in the evolution of reptiles than was previously thought. Most marine reptiles evolved from viviparous terrestrial ancestors and had probably genetic sex determination. Fossil forms often display developmental traits absent or rare among modern ones such as polydactyly, hyperphalangy, the presence of ribcage armour, reduction of head ornamentation during ontogeny, extreme modifications of vertebral count or a wide range of feather-like structures. Thus, they provide an empirical background for many morphogenetic considerations. PMID:26154335

  2. The fossil record of ecdysis, and trends in the moulting behaviour of trilobites.

    PubMed

    Daley, Allison C; Drage, Harriet B

    2016-03-01

    Ecdysis, the process of moulting an exoskeleton, is one of the key characters uniting arthropods, nematodes and a number of smaller phyla into Ecdysozoa. The arthropod fossil record, particularly trilobites, eurypterids and decapod crustaceans, yields information on moulting, although the current focus is predominantly descriptive and lacks a broader evolutionary perspective. We here review literature on the fossil record of ecdysis, synthesising research on the behaviour, evolutionary trends, and phylogenetic significance of moulting throughout the Phanerozoic. Approaches vary widely between taxonomic groups, but an overall theme uniting these works suggests that identifying moults in the palaeontological record must take into account the morphology, taphonomy and depositional environment of fossils. We also quantitatively analyse trends in trilobite ecdysis based on a newly generated database of published incidences of moulting behaviour. This preliminary work reveals significant taxonomic and temporal signal in the trilobite moulting fossil record, with free cheek moulting being prevalent across all Orders and throughout the Phanerozoic, and peaks of cephalic moulting in Phacopida during the Ordovician and rostral plate moulting in Redlichiida during the Cambrian. This study and a review of the literature suggest that it is feasible to extract large-scale evolutionary information from the fossil record of moulting. PMID:26431634

  3. Discriminating signal from noise in the fossil record of early vertebrates reveals cryptic evolutionary history

    PubMed Central

    Sansom, Robert S.; Randle, Emma; Donoghue, Philip C. J.

    2015-01-01

    The fossil record of early vertebrates has been influential in elucidating the evolutionary assembly of the gnathostome bodyplan. Understanding of the timing and tempo of vertebrate innovations remains, however, mired in a literal reading of the fossil record. Early jawless vertebrates (ostracoderms) exhibit restriction to shallow-water environments. The distribution of their stratigraphic occurrences therefore reflects not only flux in diversity, but also secular variation in facies representation of the rock record. Using stratigraphic, phylogenetic and palaeoenvironmental data, we assessed the veracity of the fossil records of the jawless relatives of jawed vertebrates (Osteostraci, Galeaspida, Thelodonti, Heterostraci). Non-random models of fossil recovery potential using Palaeozoic sea-level changes were used to calculate confidence intervals of clade origins. These intervals extend the timescale for possible origins into the Upper Ordovician; these estimates ameliorate the long ghost lineages inferred for Osteostraci, Galeaspida and Heterostraci, given their known stratigraphic occurrences and stem–gnathostome phylogeny. Diversity changes through the Silurian and Devonian were found to lie within the expected limits predicted from estimates of fossil record quality indicating that it is geological, rather than biological factors, that are responsible for shifts in diversity. Environmental restriction also appears to belie ostracoderm extinction and demise rather than competition with jawed vertebrates. PMID:25520359

  4. Assessing the fidelity of the fossil record by using marine bivalves

    PubMed Central

    Valentine, James W.; Jablonski, David; Kidwell, Susan; Roy, Kaustuv

    2006-01-01

    Taxa that fail to become incorporated into the fossil record can reveal much about the biases of this record and provide the information needed to correct such biases in empirical analyses of the history of life. Yet little is known about the characteristics of taxa missing from the fossil record. For the marine Bivalvia, which have become a model system for macroevolutionary and macroecological analysis in the fossil record, 308 of the 1,292 living genera and subgenera (herein termed “taxa”) are not recorded as fossils. These missing taxa are not a random sample of the clade, but instead tend to have small body size, reactive shell structures, commensal or parasitic habit, deep-sea distribution, narrow geographic range, restriction to regions exposing few Neogene marine sediments, or recent date of formal taxonomic description in the neontological literature. Most missing taxa show two or more of these features and tend to be concentrated in particular families. When we exclude the smallest taxa (<1 cm) and deep-sea endemics, date of published description and geographic range become the strongest predictors of the missing taxa; other factors are statistically insignificant or have relatively small effects. These biases might influence a variety of analyses including the use of fossil data in support of phylogenetic analyses, molecular clock calibrations, and analyses of spatial and temporal dynamics of clades and biotas. Clade inventories such as these can be used to develop protocols that minimize the biases imposed by sampling and preservation. PMID:16617108

  5. Methods for the quantitative comparison of molecular estimates of clade age and the fossil record.

    PubMed

    Clarke, Julia A; Boyd, Clint A

    2015-01-01

    Approaches quantifying the relative congruence, or incongruence, of molecular divergence estimates and the fossil record have been limited. Previously proposed methods are largely node specific, assessing incongruence at particular nodes for which both fossil data and molecular divergence estimates are available. These existing metrics, and other methods that quantify incongruence across topologies including entirely extinct clades, have so far not taken into account uncertainty surrounding both the divergence estimates and the ages of fossils. They have also treated molecular divergence estimates younger than previously assessed fossil minimum estimates of clade age as if they were the same as cases in which they were older. However, these cases are not the same. Recovered divergence dates younger than compared oldest known occurrences require prior hypotheses regarding the phylogenetic position of the compared fossil record and standard assumptions about the relative timing of morphological and molecular change to be incorrect. Older molecular dates, by contrast, are consistent with an incomplete fossil record and do not require prior assessments of the fossil record to be unreliable in some way. Here, we compare previous approaches and introduce two new descriptive metrics. Both metrics explicitly incorporate information on uncertainty by utilizing the 95% confidence intervals on estimated divergence dates and data on stratigraphic uncertainty concerning the age of the compared fossils. Metric scores are maximized when these ranges are overlapping. MDI (minimum divergence incongruence) discriminates between situations where molecular estimates are younger or older than known fossils reporting both absolute fit values and a number score for incompatible nodes. DIG range (divergence implied gap range) allows quantification of the minimum increase in implied missing fossil record induced by enforcing a given set of molecular-based estimates. These metrics are used

  6. Antarctic snow record of cadmium, copper, and zinc content during the twentieth century

    NASA Astrophysics Data System (ADS)

    Wolff, Eric W.; Suttie, Edward D.; Peel, David A.

    A snowpit in Coats Land, Antarctica, has been sampled in order to obtain a record of Cd, Cu and Zn covering the period 1923-1986. The snowpit record gives an indication of southern hemisphere (SH) pollution reaching Antarctica. For Zn, concentrations (averaging 1.5 ng kg -1) can be explained as arising from natural crustal dust (based on Zn/Al ratios). No increase is observed over the period of the record here, despite a large increase in emissions from smelting operations. The main emitters are near the equator, and this may explain the lack of response in the Antarctic record. For Cd, concentrations (averaging 0.1 ng kg -1) cannot easily be explained in terms of natural emissions, unless the volcanic input is dominant. No significant increase is seen in the snow for this metal also. For Cu, the natural input can explain only a small part of the concentration (averaging 3.5 ng kg -1) measured, and increased concentrations (factor 2) are seen in the 1970s and 1980s compared to earlier decades. This is consistent with increased emissions from Cu smelting activities, particularly in Chile, where emissions are relatively far south compared to the main part of SH landmasses. Cu thus joins Pb as a metal whose natural cycle has been significantly perturbed even in the Antarctic atmosphere.

  7. 30-Year Satellite Record Reveals Contrasting Arctic and Antarctic Decadal Sea Ice Variability

    NASA Technical Reports Server (NTRS)

    Cavalieri, D. J.; Parkinson, C. L.; Vinnikov, K. Y.

    2003-01-01

    A 30-year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the Arctic sea ice extent decreased by 0.30+0.03 x 10(exp 6) square kilometers per 10 yr from 1972 through 2002, but by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per 10yr from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased. Over the full 30-year period, the Antarctic ice extent decreased by 0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10 yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent in the early 1970's, an anomaly that apparently began in the late 1960's, as observed in early visible and infrared satellite images.

  8. Halogen species record Antarctic sea ice extent over glacial-interglacial periods

    NASA Astrophysics Data System (ADS)

    Spolaor, A.; Vallelonga, P.; Plane, J. M. C.; Kehrwald, N.; Gabrieli, J.; Varin, C.; Turetta, C.; Cozzi, G.; Boutron, C.; Barbante, C.

    2013-02-01

    Sea ice is an integral part of the Earth's climate system because it affects planetary albedo, sea surface salinity, and the atmosphere-ocean exchange of reactive gases and aerosols. Bromine and iodine chemistry is active at polar sea ice margins with the occurrence of bromine explosions and the biological production of organo-iodine from sea ice algae. Satellite measurements demonstrate that concentrations of bromine oxide (BrO) and iodine oxide (IO) decrease over sea ice toward the Antarctic interior. Here we present speciation measurements of bromine and iodine in the TALDICE (TALos Dome Ice CorE) ice core (159°11' E, 72°49' S, 2315 m a.s.l.) spanning the last 215 ky. The Talos Dome ice core is located 250 km inland and is sensitive to marine air masses intruding onto the Antarctic Plateau. Talos Dome bromide (Br-) is positively correlated with temperature and negatively correlated with sodium (Na). Based on the Br-/Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I-) and iodate (IO3-), peaks during glacials with lower values during interglacial periods. Although IO3- is considered the most stable iodine species in the atmosphere it was only observed in the TALDICE record during glacial maxima. Sea ice dynamics are arguably the primary driver of halogen fluxes over glacial-interglacial timescales, by altering the distance between the sea ice edge and the Antarctic plateau and by altering the surface area of sea ice available to algal colonization. Based on our results we propose the use of both halogens for examining Antarctic variability of past sea ice extent.

  9. Halogen species record Antarctic sea ice extent over glacial-interglacial periods

    NASA Astrophysics Data System (ADS)

    Spolaor, A.; Vallelonga, P.; Plane, J. M. C.; Kehrwald, N.; Gabrieli, J.; Varin, C.; Turetta, C.; Cozzi, G.; Kumar, R.; Boutron, C.; Barbante, C.

    2013-07-01

    Sea ice is an integral part of the earth's climate system because it affects planetary albedo, sea-surface salinity, and the atmosphere-ocean exchange of reactive gases and aerosols. Bromine and iodine chemistry is active at polar sea ice margins with the occurrence of bromine explosions and the biological production of organoiodine from sea ice algae. Satellite measurements demonstrate that concentrations of bromine oxide (BrO) and iodine oxide (IO) decrease over sea ice toward the Antarctic interior. Here we present speciation measurements of bromine and iodine in the TALDICE (TALos Dome Ice CorE) ice core (159°11' E, 72°49' S; 2315 m a.s.l.) spanning the last 215 ky. The Talos Dome ice core is located 250 km inland and is sensitive to marine air masses intruding onto the Antarctic Plateau. Talos Dome bromide (Br-) is positively correlated with temperature and negatively correlated with sodium (Na). Based on the Br-/Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I-) and iodate (IO3-), peaks during glacials with lower values during interglacial periods. Although IO3- is considered the most stable iodine species in the atmosphere it was only observed in the TALDICE record during glacial maxima. Sea ice dynamics are arguably the primary driver of halogen fluxes over glacial-interglacial timescales, by altering the distance between the sea ice edge and the Antarctic plateau and by altering the surface area of sea ice available to algal colonization. Based on our results we propose the use of both halogens for examining Antarctic variability of past sea ice extent.

  10. 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.

  11. Completeness of the fossil record: Estimating losses due to small body size

    NASA Astrophysics Data System (ADS)

    Cooper, Roger A.; Maxwell, Phillip A.; Crampton, James S.; Beu, Alan G.; Jones, Craig M.; Marshall, Bruce A.

    2006-04-01

    Size bias in the fossil record limits its use for interpreting patterns of past biodiversity and ecological change. Using comparative size frequency distributions of exceptionally good regional records of New Zealand Holocene and Cenozoic Mollusca in museum archive collections, we derive first-order estimates of the magnitude of the bias against small body size and the effect of this bias on completeness of the fossil record. Our database of 3907 fossil species represents an original living pool of 9086 species, from which ˜36% have been removed by size culling, 27% from the smallest size class (<5 mm). In contrast, non-size-related losses compose only 21% of the total. In soft rocks, the loss of small taxa can be reduced by nearly 50% through the employment of exhaustive collection and preparation techniques.

  12. Experimental analysis of decay biases in the fossil record of lobopodians

    NASA Astrophysics Data System (ADS)

    Murdock, Duncan; Gabbott, Sarah; Purnell, Mark

    2016-04-01

    If fossils are to realize their full potential in reconstructing the tree of life we must understand how our view of ancient organisms is obscured by taphonomic filters of decay and preservation. In most cases, processes of decay will leave behind either nothing or only the most decay resistant body parts, and even in those rare instances where soft tissues are fossilized we cannot assume that the resulting fossil, however exquisite, represents a faithful anatomical representation of the animal as it was in life.Recent experiments have shown that the biases introduced by decay can be far from random; in chordates, for example, the most phylogenetically informative characters are also the most decay-prone, resulting in 'stemward slippage'. But how widespread is this phenomenon, and are there other non-random biases linked to decay? Intuitively, we make assumptions about the likelihood of different kinds of characters to survive and be preserved, with knock-on effects for anatomical and phylogenetic interpretations. To what extent are these assumptions valid? We combine our understanding of the fossil record of lobopodians with insights from decay experiments of modern onychophorans (velvet worms) to test these assumptions. Our analysis demonstrates that taphonomically informed tests of character interpretations have the potential to improve phylogenetic resolution. This approach is widely applicable to the fossil record - allowing us to ground-truth some of the assumptions involved in describing exceptionally preserved fossil material.

  13. Phanerozoic marine biodiversity dynamics in light of the incompleteness of the fossil record

    PubMed Central

    Lu, Peter J.; Yogo, Motohiro; Marshall, Charles R.

    2006-01-01

    Long-term evolutionary dynamics have been approached through quantitative analysis of the fossil record, but without explicitly taking its incompleteness into account. Here we explore the temporal covariance structure of per-genus origination and extinction rates for global marine fossil genera throughout the Phanerozoic, both before and after corrections for the incompleteness of the fossil record. Using uncorrected data based on Sepkoski’s compendium, we find significant autocovariance within origination and extinction rates, as well as covariance between extinction and origination, not one, but two, intervals later, corroborating evidence for the unexplained temporal gap found by past studies. However, these effects vanish when the data are corrected for the incompleteness of the fossil record. Instead, we observe significant covariance only between extinction and origination in the immediately following intervals. The gap in the response of the biosphere to extinction in the uncorrected fossil record thus appears to be an artifact of the incompleteness of the fossil record, specifically due to episodic variation in the probability that taxa will be preserved, on time scales comparable to the temporal resolution of Sepkoski’s data. Our results also indicate that at that temporal resolution (the stage/substage of duration ≈5 million years), changes in origination and extinction do not persist for longer than one interval, except that elevated origination rates immediately after extinction may last for more than a single interval. Thus, although certain individual cases may deviate from the overall pattern, we find that in general the biosphere’s response to perturbation is immediate geologically and usually short-lived. PMID:16477008

  14. Phanerozoic marine biodiversity dynamics in light of the incompleteness of the fossil record.

    PubMed

    Lu, Peter J; Yogo, Motohiro; Marshall, Charles R

    2006-02-21

    Long-term evolutionary dynamics have been approached through quantitative analysis of the fossil record, but without explicitly taking its incompleteness into account. Here we explore the temporal covariance structure of per-genus origination and extinction rates for global marine fossil genera throughout the Phanerozoic, both before and after corrections for the incompleteness of the fossil record. Using uncorrected data based on Sepkoski's compendium, we find significant autocovariance within origination and extinction rates, as well as covariance between extinction and origination, not one, but two, intervals later, corroborating evidence for the unexplained temporal gap found by past studies. However, these effects vanish when the data are corrected for the incompleteness of the fossil record. Instead, we observe significant covariance only between extinction and origination in the immediately following intervals. The gap in the response of the biosphere to extinction in the uncorrected fossil record thus appears to be an artifact of the incompleteness of the fossil record, specifically due to episodic variation in the probability that taxa will be preserved, on time scales comparable to the temporal resolution of Sepkoski's data. Our results also indicate that at that temporal resolution (the stage/substage of duration approximately = 5 million years), changes in origination and extinction do not persist for longer than one interval, except that elevated origination rates immediately after extinction may last for more than a single interval. Thus, although certain individual cases may deviate from the overall pattern, we find that in general the biosphere's response to perturbation is immediate geologically and usually short-lived. PMID:16477008

  15. 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.

  16. Impact theory of mass extinctions and the invertebrate fossil record

    SciTech Connect

    Alvarez, W.; Kauffman, E.G.; Surlyk, F.; Alvarez, L.W.; Asaro, F.; Michel, H.V.

    1984-03-16

    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. 50 references, 4 figures.

  17. Extant-only comparative methods fail to recover the disparity preserved in the bird fossil record.

    PubMed

    Mitchell, Jonathan S

    2015-09-01

    Most extant species are in clades with poor fossil records, and recent studies of comparative methods show they have low power to infer even highly simplified models of trait evolution without fossil data. Birds are a well-studied radiation, yet their early evolutionary patterns are still contentious. The fossil record suggests that birds underwent a rapid ecological radiation after the end-Cretaceous mass extinction, and several smaller, subsequent radiations. This hypothesized series of repeated radiations from fossil data is difficult to test using extant data alone. By uniting morphological and phylogenetic data on 604 extant genera of birds with morphological data on 58 species of extinct birds from 50 million years ago, the "halfway point" of avian evolution, I have been able to test how well extant-only methods predict the diversity of fossil forms. All extant-only methods underestimate the disparity, although the ratio of within- to between-clade disparity does suggest high early rates. The failure of standard models to predict high early disparity suggests that recent radiations are obscuring deep time patterns in the evolution of birds. Metrics from different models can be used in conjunction to provide more valuable insights than simply finding the model with the highest relative fit. PMID:26257156

  18. The avian fossil record in Insular Southeast Asia and its implications for avian biogeography and palaeoecology

    PubMed Central

    2014-01-01

    Excavations and studies of existing collections during the last decades have significantly increased the abundance as well as the diversity of the avian fossil record for Insular Southeast Asia. The avian fossil record covers the Eocene through the Holocene, with the majority of bird fossils Pleistocene in age. Fossil bird skeletal remains represent at least 63 species in 54 genera and 27 families, and two ichnospecies are represented by fossil footprints. Birds of prey, owls and swiftlets are common elements. Extinctions seem to have been few, suggesting continuity of avian lineages since at least the Late Pleistocene, although some shifts in species ranges have occurred in response to climatic change. Similarities between the Late Pleistocene avifaunas of Flores and Java suggest a dispersal route across southern Sundaland. Late Pleistocene assemblages of Niah Cave (Borneo) and Liang Bua (Flores) support the rainforest refugium hypothesis in Southeast Asia as they indicate the persistence of forest cover, at least locally, throughout the Late Pleistocene and Holocene. PMID:24688871

  19. The Completeness of the Fossil Record of Mesozoic Birds: Implications for Early Avian Evolution

    PubMed Central

    Brocklehurst, Neil; Upchurch, Paul; Mannion, Philip D.; O'Connor, Jingmai

    2012-01-01

    Many palaeobiological analyses have concluded that modern birds (Neornithes) radiated no earlier than the Maastrichtian, whereas molecular clock studies have argued for a much earlier origination. Here, we assess the quality of the fossil record of Mesozoic avian species, using a recently proposed character completeness metric which calculates the percentage of phylogenetic characters that can be scored for each taxon. Estimates of fossil record quality are plotted against geological time and compared to estimates of species level diversity, sea level, and depositional environment. Geographical controls on the avian fossil record are investigated by comparing the completeness scores of species in different continental regions and latitudinal bins. Avian fossil record quality varies greatly with peaks during the Tithonian-early Berriasian, Aptian, and Coniacian–Santonian, and troughs during the Albian-Turonian and the Maastrichtian. The completeness metric correlates more strongly with a ‘sampling corrected’ residual diversity curve of avian species than with the raw taxic diversity curve, suggesting that the abundance and diversity of birds might influence the probability of high quality specimens being preserved. There is no correlation between avian completeness and sea level, the number of fluviolacustrine localities or a recently constructed character completeness metric of sauropodomorph dinosaurs. Comparisons between the completeness of Mesozoic birds and sauropodomorphs suggest that small delicate vertebrate skeletons are more easily destroyed by taphonomic processes, but more easily preserved whole. Lagerstätten deposits might therefore have a stronger impact on reconstructions of diversity of smaller organisms relative to more robust forms. The relatively poor quality of the avian fossil record in the Late Cretaceous combined with very patchy regional sampling means that it is possible neornithine lineages were present throughout this interval but

  20. Forced sea-level change in a forearc basin related to subduction of a spreading ridge: the Fossil Bluff Group (Jurassic-Cretaceous), Alexander Island, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Macdonald, David

    2015-04-01

    During the Mesozoic, the Antarctic Peninsula was the site of an active volcanic arc related to the eastwards subduction of proto-Pacific oceanic crust. Alexander Island is the largest of the many islands that lie on the western (fore-arc) side of the Antarctic Peninsula; it forms one of the best-exposed ancient fore-arcs in the world. The pre-Tertiary rocks can be divided into two main units. The LeMay Group (Jurassic-Tertiary) forms the structural basement to Alexander Island and comprises greenschist-facies metasedimentary rocks. It is interpreted as a Mesozoic accretionary prism. The Fossil Bluff Group unconformably overlies and is faulted against the LeMay Group; it represents the sedimentary fill of a coeval fore-arc basin. Subduction ceased due to a series of Cenozoic ridge-trench collisions which began off Alexander Island at 50 Ma and got progressively younger to the north. However, the approach of the ridge can be inferred from the Mesozoic deposits of the Fossil Bluff Group (Jurassic-Cretaceous) in Alexander Island. In this paper, I will show that the ocean floor being subducted became progressively shallower through Jurassic and Cretaceous time (by at least 1,000 m). The result in the forearc basin was a sudden shallowing in water depths from at least 1,000 m at 125 Ma, to emergent at 100 Ma. This forced shallowing ended sedimentation in the basin and resulted in considerable topography on Alexander Island that persists to the present day.

  1. Fossilized embryos are widespread but the record is temporally and taxonomically biased

    USGS Publications Warehouse

    Donoghue, P.C.J.; Kouchinsky, A.; Waloszek, Dieter; Bengtson, S.; Dong, X.-P.; Val'Kov, A.K.; Cunningham, J.A.; Repetski, J.E.

    2006-01-01

    We report new discoveries of embryos and egg capsules from the Lower Cambrian of Siberia, Middle Cambrian of Australia and Lower Ordovician of North America. Together with existing records, embryos have now been recorded from four of the seven continents. However, the new discoveries highlight secular and systematic biases in the fossil record of embryonic stages. The temporal window within which the embryos and egg capsules are found is of relatively short duration; it ends in the Early Ordovician and is roughly coincident with that of typical "Orsten"-type faunas. The reduced occurrence of such fossils has been attributed to reducing levels of phosphate in marine waters during the early Paleozoic, but may also be owing to the increasing depth of sediment mixing by infaunal metazoans. Furthermore, most records younger than the earliest Cambrian are of a single kind - large eggs and embryos of the priapulid-like scalidophoran Markuelia. We explore alternative explanations for the low taxonomic diversity of embryos recovered thus far, including sampling, size, anatomy, ecology, and environment, concluding that the preponderance of Markuelia embryos is due to its precocious development of cuticle at an embryonic stage, predisposing it to preservation through action as a substrate on which microbially mediated precipitation of authigenic calcium phosphate may occur. The fossil record of embryos may be limited to a late Neoproterozoic to early Ordovician snapshot that is subject to dramatic systematic bias. Together, these biases must be considered seriously in attempts to use the fossil record to arbitrate between hypotheses of developmental and life history evolution implicated in the origin of metazoan clades. ?? 2006 Blackwell Publishing Ltd.

  2. The Antarctic record of Pliocene warmth and its expression in the AND-1B drillcore

    NASA Astrophysics Data System (ADS)

    Winter, Diane; Sjunneskog, Charlotte

    2010-05-01

    The potential for comparison of the now well-accepted Pliocene warmth to the current effects of modern climate change has made the topic of the extent and global expression of this warmth one of great interest. This time period is uniquely recorded in the ANDRILL McMurdo Ice Shelf Project AND-1B drillcore by a stratigraphic interval representing extended depositional conditions characterized by a highly-productive open-marine environment. Nearly 100-m of diatomite and diatom-rich sediments preserve three distinct time intervals, which chronostratigraphic controls suggest represent deposition during 3.33-3.6 Ma, 4.3-4.5 Ma and ~4.6 Ma. This record is extraordinary both in its extent as well as its proximity to the Antarctic continent. The diatom assemblages preserving these time intervals record a marine environment quite different than occurs today in the Ross Sea. Species such as Shionodiscus tetraoestrupii, Stellarima stellaris and Thalassionema nitzschioides are common throughout this 100m interval while they currently are observed only in waters closer to and north of the modern Polar Frontal Zone. Sea surface temperature estimates from these species suggest conditions 3-5°C warmer than present in southern McMurdo Sound. Additionally, often low numbers of clasts within the diatomite and diatom-rich sediments corroborate a decrease in glacial and seasonal ice at the AND-1B site during this interval. Other drillcore records containing sediments from this time exist in locations both proximal to and on the Antarctic continent as well as within the Southern Ocean. Several sites in close proximity to AND-1B within McMurdo Sound (DVDP-10, DVDP-11 and CIROS-2) contain diatom-rich sediments correlative to these three intervals. The assemblages within samples from these three cores record a fjordal setting indicative of increased sea level associated with warmer marine conditions at these sites. The middle diatomite interval in AND-1B, 4.3-4.5 Ma, contains abundant

  3. Unlocking the early fossil record of the arthropod central nervous system.

    PubMed

    Edgecombe, Gregory D; Ma, Xiaoya; Strausfeld, Nicholas J

    2015-12-19

    Extant panarthropods (euarthropods, onychophorans and tardigrades) are hallmarked by stunning morphological and taxonomic diversity, but their central nervous systems (CNS) are relatively conserved. The timing of divergences of the ground pattern CNS organization of the major panarthropod clades has been poorly constrained because of a scarcity of data from their early fossil record. Although the CNS has been documented in three-dimensional detail in insects from Cenozoic ambers, it is widely assumed that these tissues are too prone to decay to withstand other styles of fossilization or geologically older preservation. However, Cambrian Burgess Shale-type compressions have emerged as sources of fossilized brains and nerve cords. CNS in these Cambrian fossils are preserved as carbon films or as iron oxides/hydroxides after pyrite in association with carbon. Experiments with carcasses compacted in fine-grained sediment depict preservation of neural tissue for a more prolonged temporal window than anticipated by decay experiments in other media. CNS and compound eye characters in exceptionally preserved Cambrian fossils predict divergences of the mandibulate and chelicerate ground patterns by Cambrian Stage 3 (ca 518 Ma), a dating that is compatible with molecular estimates for these splits. PMID:26554038

  4. Diversity-dependence brings molecular phylogenies closer to agreement with the fossil record.

    PubMed

    Etienne, Rampal S; Haegeman, Bart; Stadler, Tanja; Aze, Tracy; Pearson, Paul N; Purvis, Andy; Phillimore, Albert B

    2012-04-01

    The branching times of molecular phylogenies allow us to infer speciation and extinction dynamics even when fossils are absent. Troublingly, phylogenetic approaches usually return estimates of zero extinction, conflicting with fossil evidence. Phylogenies and fossils do agree, however, that there are often limits to diversity. Here, we present a general approach to evaluate the likelihood of a phylogeny under a model that accommodates diversity-dependence and extinction. We find, by likelihood maximization, that extinction is estimated most precisely if the rate of increase in the number of lineages in the phylogeny saturates towards the present or first decreases and then increases. We demonstrate the utility and limits of our approach by applying it to the phylogenies for two cases where a fossil record exists (Cetacea and Cenozoic macroperforate planktonic foraminifera) and to three radiations lacking fossil evidence (Dendroica, Plethodon and Heliconius). We propose that the diversity-dependence model with extinction be used as the standard model for macro-evolutionary dynamics because of its biological realism and flexibility. PMID:21993508

  5. Unlocking the early fossil record of the arthropod central nervous system

    PubMed Central

    Edgecombe, Gregory D.; Ma, Xiaoya; Strausfeld, Nicholas J.

    2015-01-01

    Extant panarthropods (euarthropods, onychophorans and tardigrades) are hallmarked by stunning morphological and taxonomic diversity, but their central nervous systems (CNS) are relatively conserved. The timing of divergences of the ground pattern CNS organization of the major panarthropod clades has been poorly constrained because of a scarcity of data from their early fossil record. Although the CNS has been documented in three-dimensional detail in insects from Cenozoic ambers, it is widely assumed that these tissues are too prone to decay to withstand other styles of fossilization or geologically older preservation. However, Cambrian Burgess Shale-type compressions have emerged as sources of fossilized brains and nerve cords. CNS in these Cambrian fossils are preserved as carbon films or as iron oxides/hydroxides after pyrite in association with carbon. Experiments with carcasses compacted in fine-grained sediment depict preservation of neural tissue for a more prolonged temporal window than anticipated by decay experiments in other media. CNS and compound eye characters in exceptionally preserved Cambrian fossils predict divergences of the mandibulate and chelicerate ground patterns by Cambrian Stage 3 (ca 518 Ma), a dating that is compatible with molecular estimates for these splits. PMID:26554038

  6. Fossil invertebrates records in cave sediments and paleoenvironmental assessments: a study of four cave sites from Romanian Carpathians

    NASA Astrophysics Data System (ADS)

    Moldovan, O. T.; Constantin, S.; Panaiotu, C.; Roban, R. D.; Frenzel, P.; Miko, L.

    2015-06-01

    Fossil invertebrates from cave sediments have been recently described as a potential new proxy for paleoenvironment and used in cross-correlations with alternate proxy records from cave deposits. Here we present the results of a fossil invertebrates study in four caves from two climatically different regions of the Romanian Carpathians, to complement paleoenvironmental data previously reported. Oribatid mites and ostracods are the most common invertebrates in the studied cave sediments. Some of the identified taxa are new for science, and most of them are indicative for either warm/cold stages or dry/wetter oscillations. In two caves the fossil invertebrates records indicate rapid climate oscillations during times known for a relatively stable climate. By corroborating the fossil invertebrates' record with the information given by magnetic properties and sediment structures, complementary data on past vegetation, temperatures, and hydraulic regimes could be gathered. This paper analyses the potential of fossil invertebrate records as a paleoenvironmental proxy, potential problems and pitfalls.

  7. Antarctic climate variability from ice core records over the last two millennia

    NASA Astrophysics Data System (ADS)

    Braida, Martina; Stenni, Barbara; Masson-Delmotte, Valerie; Dreossi, Giuliano; Oerter, Hans; Selmo, Enricomaria; Severi, Mirko; Goosse, Hugues; Mezgec, Karin

    2013-04-01

    The climate of the past can be successfully investigated through the study of polar ice sheets. Paleotemperature reconstructions from Antarctic ice cores are based on water isotope profiles, thanks to the existing relationship between δ18O (or δD) and the temperature at the site. Here we present the climate record of the past 2000 years resulting from the stable isotope analysis of the ice core drilled at Talos Dome in East Antarctica from 2003 to 2007 in the framework of the European TALDICE (TALos Dome Ice CorE) project. Talos Dome (72°49'S, 159°11'E; 2315 m; -41°C) is an ice dome on the edge of the East Antarctic plateau. The snow accumulation rate of the site (80 kg m-2 yr-1) allows extracting high-resolution data for the past millennia. The main moisture sources of snow precipitation at this near-coastal site are located in the Indian Ocean and the Ross Sea. Isotopic analyses of TALDICE detailed (10 cm) samples have been performed in the framework of the ESF-HOLOCLIP project, whose main objective is to integrate the ice core, the marine core and the modeling data to investigate the climate variability of the high latitude southern hemisphere over the Holocene. The isotopic record obtained from the TALDICE ice core is here compared with a shallow firn core (89 m long) previously drilled at Talos Dome, at a 5 km distance, and covering the past 800 years. The two isotopic records are stacked to reduce the stratigraphic noise and compared with other available isotopic records from Antarctica to highlight common trends and regional variability in the climatic signal over the past two millennia. We compare the data with a simulation performed with a three-dimensional earth system model of intermediate complexity (LOVECLIM) with and without data assimilation. Considering the δ18O profile from the TALDICE ice core and comparing it with the ones from the other available records we can observe common negative isotopic anomalies in the period from about 1450 to

  8. Mass extinctions in the fossil record of late Palaeozoic and Mesozoic tetrapods

    NASA Astrophysics Data System (ADS)

    Benton, Michael J.

    The fossil record of tetrapods is very patchy because of the problems of preservation in terrestrial sediments, and because vertebrates are rarely very abundant. However, the fossil record of tetrapods has the advantages that it is easier to establish a phylogenetic taxonomy than for many invertebrate groups (many characters; fast evolution), and there is the potential for more detailed ecological analyses (greater knowledge of modern tetrapod ecology). The diversity of tetrapods increased during the Devonian, the Carboniferous, and the Permian, but it remained generally constant during the Triassic, the Jurassic, and the Early Cretaceous. Overall diversity then began to increase in the Late Cretaceous, and continued to do so during the Tertiary. The rapid radiation of modern tetrapod groups — frogs, salamanders, lizards, snakes, turtles, crocodiles, birds and mammals — was hardly affected by the celebrated end-Cretaceous extinction event.

  9. Seismic stratigraphy of the Antarctic Peninsula pacific margin: A record of Pliocene-Pleistocene ice volume and paleoclimate

    SciTech Connect

    Larter, R.D.; Barker, P.F. )

    1989-08-01

    Multichannel seismic profiles across the Pacific margin of the Antarctic Peninsula show a series of oblique progradational sequences. These sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum. Reflection events from deeper stratigraphic levels, followed down the continental slope and onto the rise, overlie ocean crust of known age, showing that at least eight such glacial sequences have been deposited within the past 6 m.y. Similar groundings have probably occurred on most Antarctic margins, but the depositional record is particularly well preserved at this margin because of Pliocene-Pleistocene thermal subsidence. Neogene global sea-level fluctuations have been attributed to changes in volume of continental ice sheets. The depositional sequences on the Pacific margin of the Antarctic Peninsula are thought to record West Antarctic ice-sheet fluctuations directly. Further investigation of these sequences would assess the relation between fluctuations in ice volume and the low-latitude record of global sea-level change.

  10. An Analytical Approach for Estimating Fossil Record and Diversification Events in Sharks, Skates and Rays

    PubMed Central

    Guinot, Guillaume; Adnet, Sylvain; Cappetta, Henri

    2012-01-01

    Background Modern selachians and their supposed sister group (hybodont sharks) have a long and successful evolutionary history. Yet, although selachian remains are considered relatively common in the fossil record in comparison with other marine vertebrates, little is known about the quality of their fossil record. Similarly, only a few works based on specific time intervals have attempted to identify major events that marked the evolutionary history of this group. Methodology/Principal Findings Phylogenetic hypotheses concerning modern selachians’ interrelationships are numerous but differ significantly and no consensus has been found. The aim of the present study is to take advantage of the range of recent phylogenetic hypotheses in order to assess the fit of the selachian fossil record to phylogenies, according to two different branching methods. Compilation of these data allowed the inference of an estimated range of diversity through time and evolutionary events that marked this group over the past 300 Ma are identified. Results indicate that with the exception of high taxonomic ranks (orders), the selachian fossil record is by far imperfect, particularly for generic and post-Triassic data. Timing and amplitude of the various identified events that marked the selachian evolutionary history are discussed. Conclusion/Significance Some identified diversity events were mentioned in previous works using alternative methods (Early Jurassic, mid-Cretaceous, K/T boundary and late Paleogene diversity drops), thus reinforcing the efficiency of the methodology presented here in inferring evolutionary events. Other events (Permian/Triassic, Early and Late Cretaceous diversifications; Triassic/Jurassic extinction) are newly identified. Relationships between these events and paleoenvironmental characteristics and other groups’ evolutionary history are proposed. PMID:22957091

  11. Camellia nanningensis sp. nov.: the earliest fossil wood record of the genus Camellia (Theaceae) from East Asia.

    PubMed

    Huang, Lu-Liang; Jin, Jian-Hua; Quan, Cheng; Oskolski, Alexei A

    2016-09-01

    A new species Camellia nanningensis was described on the basis of well-preserved mummified wood from the upper Oligocene Yongning Formation of Nanning Basin in Guangxi Province, South China. This represents the most ancient fossil wood assigned to Camellia, and the earliest fossil record of the family Theaceae in China. This fossil material shows that Camellia occurred in China as early as the late Oligocene, suggesting more ancient radiation of this genus than estimated by molecular dating. PMID:27379410

  12. Developmental palaeontology in synapsids: the fossil record of ontogeny in mammals and their closest relatives.

    PubMed

    Sánchez-Villagra, Marcelo R

    2010-04-22

    The study of fossilized ontogenies in mammals is mostly restricted to postnatal and late stages of growth, but nevertheless can deliver great insights into life history and evolutionary mechanisms affecting all aspects of development. Fossils provide evidence of developmental plasticity determined by ecological factors, as when allometric relations are modified in species which invaded a new space with a very different selection regime. This is the case of dwarfing and gigantism evolution in islands. Skeletochronological studies are restricted to the examination of growth marks mostly in the cement and dentine of teeth and can provide absolute age estimates. These, together with dental replacement data considered in a phylogenetic context, provide life-history information such as maturation time and longevity. Palaeohistology and dental replacement data document the more or less gradual but also convergent evolution of mammalian growth features during early synapsid evolution. Adult phenotypes of extinct mammals can inform developmental processes by showing a combination of features or levels of integration unrecorded in living species. Some adult features such as vertebral number, easily recorded in fossils, provide indirect information about somitogenesis and hox-gene expression boundaries. Developmental palaeontology is relevant for the discourse of ecological developmental biology, an area of research where features of growth and variation are fundamental and accessible among fossil mammals. PMID:20071389

  13. Developmental palaeontology in synapsids: the fossil record of ontogeny in mammals and their closest relatives

    PubMed Central

    Sánchez-Villagra, Marcelo R.

    2010-01-01

    The study of fossilized ontogenies in mammals is mostly restricted to postnatal and late stages of growth, but nevertheless can deliver great insights into life history and evolutionary mechanisms affecting all aspects of development. Fossils provide evidence of developmental plasticity determined by ecological factors, as when allometric relations are modified in species which invaded a new space with a very different selection regime. This is the case of dwarfing and gigantism evolution in islands. Skeletochronological studies are restricted to the examination of growth marks mostly in the cement and dentine of teeth and can provide absolute age estimates. These, together with dental replacement data considered in a phylogenetic context, provide life-history information such as maturation time and longevity. Palaeohistology and dental replacement data document the more or less gradual but also convergent evolution of mammalian growth features during early synapsid evolution. Adult phenotypes of extinct mammals can inform developmental processes by showing a combination of features or levels of integration unrecorded in living species. Some adult features such as vertebral number, easily recorded in fossils, provide indirect information about somitogenesis and hox-gene expression boundaries. Developmental palaeontology is relevant for the discourse of ecological developmental biology, an area of research where features of growth and variation are fundamental and accessible among fossil mammals. PMID:20071389

  14. The fossil record, function, and possible origins of shell color patterns in Paleozoic marine invertebrates

    SciTech Connect

    Kobluk, D.R. ); Mapes, R.H. )

    1989-02-01

    Fossil invertebrate shells and carapaces displaying preserved original color patterns are among the rarest fossils. The fossil record of color patterns extends into the Middle Cambrian where the trilobite Anomocare displays a fan-like array of stripes on the pygidium. About 180 Paleozic genera are known with patterns, including trilobites, cephalopods, gastropods, brachiopods, bivalves, crinoids, and crustaceans. Based upon an analysis of these taxa, it appears that patterns and pigments in middle and late Paleozoic invertebrates may have served several functions such as warning displays, light screening, camouflage, or waste disposal. However, the presence of color patterns in fossil invertebrates in the early Paleozoic may have developed prior to the evolution of vision sufficiently sophisticated to see them. This suggests that camouflage and warning displays were not the original functions of color patterns, and that in the earliest Paleozoic they may not have been functional. The authors propose a hypothesis that involves three developmental phases in the evolution of invertebrate color patterns: (1) the incorporation of metabolic by-products, perhaps some pigmented and some not pigmented, into shells and carapaces as a means of disposal of dietary or metabolic wastes, (2) use of these pigments and patterns as an environmental adaptation, such as light screening, and (3) display during and following the evolution of vision in predators sufficiently sophisticated to see the patterns.

  15. Late Paleocene fossils from the Cerrejon Formation, Colombia, are the earliest record of Neotropical rainforest.

    PubMed

    Wing, Scott L; Herrera, Fabiany; Jaramillo, Carlos A; Gómez-Navarro, Carolina; Wilf, Peter; Labandeira, Conrad C

    2009-11-01

    Neotropical rainforests have a very poor fossil record, making hypotheses concerning their origins difficult to evaluate. Nevertheless, some of their most important characteristics can be preserved in the fossil record: high plant diversity, dominance by a distinctive combination of angiosperm families, a preponderance of plant species with large, smooth-margined leaves, and evidence for a high diversity of herbivorous insects. Here, we report on an approximately 58-my-old flora from the Cerrejón Formation of Colombia (paleolatitude approximately 5 degrees N) that is the earliest megafossil record of Neotropical rainforest. The flora has abundant, diverse palms and legumes and similar family composition to extant Neotropical rainforest. Three-quarters of the leaf types are large and entire-margined, indicating rainfall >2,500 mm/year and mean annual temperature >25 degrees C. Despite modern family composition and tropical paleoclimate, the diversity of fossil pollen and leaf samples is 60-80% that of comparable samples from extant and Quaternary Neotropical rainforest from similar climates. Insect feeding damage on Cerrejón fossil leaves, representing primary consumers, is abundant, but also of low diversity, and overwhelmingly made by generalist feeders rather than specialized herbivores. Cerrejón megafossils provide strong evidence that the same Neotropical rainforest families have characterized the biome since the Paleocene, maintaining their importance through climatic phases warmer and cooler than present. The low diversity of both plants and herbivorous insects in this Paleocene Neotropical rainforest may reflect an early stage in the diversification of the lineages that inhabit this biome, and/or a long recovery period from the terminal Cretaceous extinction. PMID:19833876

  16. The Marine Record of Holocene Deglaciation and Paleoclimate Change, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Minzoni, R. L.; Anderson, J. B.; Kirshner, A. E.; Wellner, J. S.; Fernandez-Vasquez, R. A.

    2010-12-01

    The Antarctic Peninsula Ice Cap (APIC) has undergone significant retreat since the Last Glacial Maximum (LGM). Several recent studies, including those of Lallemand Fjord (Shevenell, et al., 1996), Palmer Deep (Domack, et al., 2001), Bransfield Basin (Heroy, et al., 2008), Firth of Tay (Michalchuck, et al., 2009), Maxwell Bay (Milliken, et al., 2009), and Neny Fjord (Allen, et al., 2010), have applied multiple proxies to reconstruct glacial history from sediment cores. The regional trend of post-LGM retreat from marine and onshore records (e.g. Hjort et al., 1997; Ingolfsson et al., 1998) is characterized by deglaciation of the outer and mid-shelf areas mainly before 12 ka, with significant landward steps at ~14 and 11 ka that were most likely caused by rapid sea-level rise (Heroy and Anderson, 2007). This was followed by highly diachronous retreat from the rugged inner-shelf and inland areas after ~10 ka. This marks the demise of the Antarctic Peninsula Ice Sheet. Subsequently, the glacial systems became more isolated, and factors such as latitudinal climate variability, orographic effects, oceanographic effects, the size and altitude of glacial drainage basins, as well as bathymetry of individual bays and fjords, became more influential on glacial dynamics. For example, Firth of Tay, the northern-most fjord on the eastern side of Antarctic Peninsula (AP), became ice-free ~9 ka, but Herbert Sound, just to the south, was not ice-free until ~7.4 ka. On the western side of AP, however, Maxwell Bay, located in the South Shetland Islands just north of the APIC, was free of grounded ice ~14 ka, whereas Marguerite Bay, on the southwestern-most edge of the APIC, experienced rapid grounding line and ice shelf retreat ~9 ka. These records suggest a north to south component in the timing of retreat. The lag in retreat from west to east APIC indicates that a strong orographic effect insulated the eastern AP, but also implies that other influencing factors such as oceanographic

  17. Canterbury Drifts, SW Pacific Ocean: Record of Antarctic Intermediate Water Flow Since 24 Ma

    NASA Astrophysics Data System (ADS)

    Carter, R. M.

    2005-12-01

    The Canterbury Drifts were deposited in water depths between 400 and 1500 m by northward flowing, cold, intermediate depth water masses - Subantarctic Mode Water, Antarctic Intermediate Water, and their predecessor current flows. Drift accumulation started at 24 Ma, fed by terrigenous sediment derived from the newly rising Alpine Fault plate boundary in the west, which has built a progradational shelf-slope sediment prism up to 130 km wide at rates of eastward advance of up to 5.4 km/My. These regionally extensive, intermediate-depth sediment drifts can be examined in outcrop, in marine drillcore (ODP Site 1119) and at the modern seabed. The drifts comprise planar-bedded units up to several metres thick. Sand intervals have either reverse graded or sharp, erosive bases and normally graded tops. Bioturbation is moderate and the sands occur within a pervasive background of cm-scale, planar or wispy alternating muddy and sandy silts, consistent with deposition from rhythmically fluctuating bottom currents. In the Plio-Pleistocene, the sand:silt lithological rhythmicity occurs in synchroneity with Milankovitch-scale climate cycling; periods of inferred faster current flow (sand beds) mostly correspond to warm climatic intervals. The drifts vary in thickness from 300 m near the early Miocene shoreline, where they were accumulating in limited shallow water accommodation, to 2000+ m under the modern shelf edge. Mounded drifts first occur at 15 Ma (Middle Miocene), their appearance perhaps reflecting more vigorous intermediate water flow consequent upon the worldwide climatic deterioration between 15 and 13 Ma. A further change from large (more than 10 km wide) to smaller (1-3 km wide) mounded slope drifts occurs at 3.1 Ma, marking further cooling, the inception of discrete SAMW flows, and initiation of the Subantarctic Front. The natural gamma ray record from Site 1119 contains a history since 3.9 Ma of the waxing and waning of the New Zealand mountain ice cap. Back to 0

  18. Large-scale heterogeneity of the fossil record: implications for Phanerozoic biodiversity studies.

    PubMed

    Smith, A B

    2001-03-29

    Patterns of origination, extinction and standing diversity through time have been inferred from tallies of taxa preserved in the fossil record. This approach assumes that sampling of the fossil record is effectively uniform over time. Although recent evidence suggests that our sampling of the available rock record has indeed been very thorough and effective, there is also overwhelming evidence that the rock record available for sampling is itself distorted by major systematic biases. Data on rock outcrop area compiled for post-Palaeozoic sediments from Western Europe at stage level are presented. These show a strongly cyclical pattern corresponding to first- and second-order sequence stratigraphical depositional cycles. Standing diversity increases over time and, at the coarsest scale, is decoupled from surface outcrop area. This increasing trend can therefore be considered a real pattern. Changes in standing diversity and origination rates over time-scales measured in tens of millions of years, however, are strongly correlated with surface outcrop area. Extinction peaks conform to a random-walk model, but larger peaks occur at just two positions with respect to second-order stratigraphical sequences, towards the culmination of stacked transgressive system tracts and close to system bases, precisely the positions where taxonomic last occurrences are predicted to cluster under a random distribution model. Many of the taxonomic patterns that have been described from the fossil record conform to a species-area effect. Whether this arises primarily from sampling bias, or from changing surface area of marine shelf seas through time and its effect on biodiversity, remains problematic. PMID:11316484

  19. The earliest fossil record of Panorpidae (Mecoptera) from the Middle Jurassic of China

    PubMed Central

    Ding, He; Shih, Chungkun; Bashkuev, Alexei; Zhao, Yunyun; Ren, Dong

    2014-01-01

    Abstract The early history of Panorpidae (Mecoptera) is poorly known due to sparse fossil records. Up to date, only nine fossil species have been described, all from the Paleogene, except the Early Cretaceous Solusipanorpa gibbidorsa Lin, 1980. However, we suggest S. gibbidorsa is too incompletely preserved to permit even family classification. A new genus with two new species, Jurassipanorpa impunctata gen. et sp. n. and Jurassipanorpa sticta sp. n., are described based on four well-preserved specimens from the late Middle Jurassic Jiulongshan Formation of Daohugou, Inner Mongolia, China. These two new species are the earliest fossil records of Panorpidae. The new genus is erected based on a combination of forewing characters: both R1 and Rs1 with two branches, 1A reaching posterior margin of wing distad of the forking of Rs from R1, and no crossveins or only one crossvein between veins of 1A and 2A. In all four specimens, long and robust setae ranging from 0.09 to 0.38 mm in length and pointing anteriorly, are present on anal veins of forewings. The function of these setae is enigmatic. PMID:25152669

  20. Direct and indirect fossil records of megachilid bees from the Paleogene of Central Europe (Hymenoptera: Megachilidae)

    NASA Astrophysics Data System (ADS)

    Wedmann, Sonja; Wappler, Torsten; Engel, Michael S.

    2009-06-01

    Aside from pollen and nectar, bees of the subfamily Megachilinae are closely associated with plants as a source of materials for nest construction. Megachilines use resins, masticated leaves, trichomes and other plant materials sometimes along with mud to construct nests in cavities or in soil. Among these, the leafcutter bees ( Megachile s.l.) are the most famous for their behaviour to line their brood cells with discs cut from various plants. We report on fossil records of one body fossil of a new non-leafcutting megachiline and of 12 leafcuttings from three European sites—Eckfeld and Messel, both in Germany (Eocene), and Menat, France (Paleocene). The excisions include the currently earliest record of probable Megachile activity and suggest the presence of such bees in the Paleocene European fauna. Comparison with extant leafcuttings permits the interpretation of a minimal number of species that produced these excisions. The wide range of size for the leafcuttings indirectly might suggest at least two species of Megachile for the fauna of Messel in addition to the other megachiline bee described here. The presence of several cuttings on most leaves from Eckfeld implies that the preferential foraging behaviour of extant Megachile arose early in megachiline evolution. These results demonstrate that combined investigation of body and trace fossils complement each other in understanding past biodiversity, the latter permitting the detection of taxa not otherwise directly sampled and inferences on behavioural evolution.

  1. Systematics, phylogeny, and taphonomy of ghost shrimps (Decapoda): a perspective from the fossil record

    PubMed Central

    Klompmaker, Adiël A.

    2016-01-01

    Ghost shrimps of Callianassidae and Ctenochelidae are soft-bodied, usually heterochelous decapods representing major bioturbators of muddy and sandy (sub)marine substrates. Ghost shrimps have a robust fossil record spanning from the Early Cretaceous (~ 133 Ma) to the Holocene and their remains are present in most assemblages of Cenozoic decapod crustaceans. Their taxonomic interpretation is in flux, mainly because the generic assignment is hindered by their insufficient preservation and disagreement in the biological classification. Furthermore, numerous taxa are incorrectly classified within the catch-all taxon Callianassa. To show the historical patterns in describing fossil ghost shrimps and to evaluate taphonomic aspects influencing the attribution of ghost shrimp remains to higher level taxa, a database of all fossil species treated at some time as belonging to the group has been compiled: 250 / 274 species are considered valid ghost shrimp taxa herein. More than half of these taxa (160 species, 58.4%) are known only from distal cheliped elements, i.e., dactylus and / or propodus, due to the more calcified cuticle locally. Rarely, ghost shrimps are preserved in situ in burrows or in direct association with them, and several previously unpublished occurrences are reported herein. For generic assignment, fossil material should be compared to living species because many of them have modern relatives. Heterochely, intraspecific variation, ontogenetic changes and sexual dimorphism are all factors that have to be taken into account when working with fossil ghost shrimps. Distal elements are usually more variable than proximal ones. Preliminary results suggest that the ghost shrimp clade emerged not before the Hauterivian (~ 133 Ma). The divergence of Ctenochelidae and Paracalliacinae is estimated to occur within the interval of Hauterivian to Albian (133–100 Ma). Callichirinae and Eucalliacinae likely diverged later during the Late Cretaceous (100–66 Ma

  2. Fossil steroids record the appearance of Demospongiae during the Cryogenian period.

    PubMed

    Love, Gordon D; Grosjean, Emmanuelle; Stalvies, Charlotte; Fike, David A; Grotzinger, John P; Bradley, Alexander S; Kelly, Amy E; Bhatia, Maya; Meredith, William; Snape, Colin E; Bowring, Samuel A; Condon, Daniel J; Summons, Roger E

    2009-02-01

    The Neoproterozoic era (1,000-542 Myr ago) was an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals (Metazoa) and new ecosystems. Here we show that abundant sedimentary 24-isopropylcholestanes, the hydrocarbon remains of C(30) sterols produced by marine demosponges, record the presence of Metazoa in the geological record before the end of the Marinoan glaciation ( approximately 635 Myr ago). These sterane biomarkers are abundant in all formations of the Huqf Supergroup, South Oman Salt Basin, and, based on a new high-precision geochronology, constitute a continuous 100-Myr-long chemical fossil record of demosponges through the terminal Neoproterozoic and into the Early Cambrian epoch. The demosponge steranes occur in strata that underlie the Marinoan cap carbonate (>635 Myr ago). They currently represent the oldest evidence for animals in the fossil record, and are evidence for animals pre-dating the termination of the Marinoan glaciation. This suggests that shallow shelf waters in some late Cryogenian ocean basins (>635 Myr ago) contained dissolved oxygen in concentrations sufficient to support basal metazoan life at least 100 Myr before the rapid diversification of bilaterians during the Cambrian explosion. Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, approximately 713 Myr ago in Oman). PMID:19194449

  3. Multi-year record of atmospheric mercury at Dumont d'Urville, East Antarctic coast: continental outflow and oceanic influences

    NASA Astrophysics Data System (ADS)

    Angot, Hélène; Dion, Iris; Vogel, Nicolas; Legrand, Michel; Magand, Olivier; Dommergue, Aurélien

    2016-07-01

    Under the framework of the Global Mercury Observation System (GMOS) project, a 3.5-year record of atmospheric gaseous elemental mercury (Hg(0)) has been gathered at Dumont d'Urville (DDU, 66°40' S, 140°01' E, 43 m above sea level) on the East Antarctic coast. Additionally, surface snow samples were collected in February 2009 during a traverse between Concordia Station located on the East Antarctic plateau and DDU. The record of atmospheric Hg(0) at DDU reveals particularities that are not seen at other coastal sites: a gradual decrease of concentrations over the course of winter, and a daily maximum concentration around midday in summer. Additionally, total mercury concentrations in surface snow samples were particularly elevated near DDU (up to 194.4 ng L-1) as compared to measurements at other coastal Antarctic sites. These differences can be explained by the more frequent arrival of inland air masses at DDU than at other coastal sites. This confirms the influence of processes observed on the Antarctic plateau on the cycle of atmospheric mercury at a continental scale, especially in areas subject to recurrent katabatic winds. DDU is also influenced by oceanic air masses and our data suggest that the ocean plays a dual role on Hg(0) concentrations. The open ocean may represent a source of atmospheric Hg(0) in summer whereas the sea-ice surface may provide reactive halogens in spring that can oxidize Hg(0). This paper also discusses implications for coastal Antarctic ecosystems and for the cycle of atmospheric mercury in high southern latitudes.

  4. Holocene records of geomagnetic field behavior from a north-south transect along the western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Brachfeld, S. A.; Shah, D. P.; St-Onge, M.; St-Onge, G.

    2013-12-01

    Geochronology is inherently difficult when working with Antarctic margin sediments. Radiocarbon dating and oxygen isotope stratigraphy are challenging or impossible in sites with poor preservation of biogenic calcite. Radiocarbon dating of the acid insoluble organic matter (AIOM) is further complicated by organically lean sediment and the presence of reworked organic carbon or detrital carbon from sedimentary rocks. These complications limit the ability to interpret a paleoclimate record. Geomagnetic paleointensity dating is a proven 'tuning' technique that has been successfully applied in several studies around the Antarctic margin. However, the reference curves to which these sites were tuned were constructed primarily from Northern Hemisphere data. Here we present paleomagnetic secular variation (PSV) and relative paleointensity (RPI) data from three Antarctic Peninsula sites that possess independent chronologies and which have moderate to ultra-high sedimentation rates (40 - 700 cm/ka). Maxwell Bay, located in the volcanic South Shetland Islands, is an ultra-high-resolution site with strongly magnetic sediments from which the Shallow Drilling (SHALDRIL) program recovered a 108-m record spanning the last 14 ka. Outer Barilari Bay and Hugo Island Trough, which lie to the South along the western Antarctic Peninsula, are moderate resolution sites with a high proportion of biogenic silica. Maxwell Bay and Bariliari Bay are unique in that they possess homogenous sediment and uniform magnetic mineral assemblages, while also preserving biogenic calcite, a rare combination on the Antarctic margin. All three sites preserve strong, stable remanent magnetizations with an easily isolated characteristic component and MAD values generally < 2°, with the exception of turbidites, intervals with abundant dropstones, and biosiliceous ooze intervals. Inclination values fluctuate between the present-day value at the cores sites (-58°) and the geomagnetic axial dipole inclination

  5. Keratin Durability Has Implications for the Fossil Record: Results from a 10 Year Feather Degradation Experiment

    PubMed Central

    Moyer, Alison E.; Zheng, Wenxia; Schweitzer, Mary H.

    2016-01-01

    Keratinous ‘soft tissue’ structures (i.e. epidermally derived and originally non-biomineralized), include feathers, skin, claws, beaks, and hair. Despite their relatively common occurrence in the fossil record (second only to bone and teeth), few studies have addressed natural degradation processes that must occur in all organic material, including those keratinous structures that are incorporated into the rock record as fossils. Because feathers have high preservation potential and strong phylogenetic signal, in the current study we examine feathers subjected to different burial environments for a duration of ~10 years, using transmission electron microscopy (TEM) and in situ immunofluorescence (IF). We use morphology and persistence of specific immunoreactivity as indicators of preservation at the molecular and microstructural levels. We show that feather keratin is durable, demonstrates structural and microstructural integrity, and retains epitopes suitable for specific antibody recognition in even the harshest conditions. These data support the hypothesis that keratin antibody reactivity can be used to identify the nature and composition of epidermal structures in the rock record, and to address evolutionary questions by distinguishing between alpha- (widely distributed) and beta- (limited to sauropsids) keratin. PMID:27384819

  6. Keratin Durability Has Implications for the Fossil Record: Results from a 10 Year Feather Degradation Experiment.

    PubMed

    Moyer, Alison E; Zheng, Wenxia; Schweitzer, Mary H

    2016-01-01

    Keratinous 'soft tissue' structures (i.e. epidermally derived and originally non-biomineralized), include feathers, skin, claws, beaks, and hair. Despite their relatively common occurrence in the fossil record (second only to bone and teeth), few studies have addressed natural degradation processes that must occur in all organic material, including those keratinous structures that are incorporated into the rock record as fossils. Because feathers have high preservation potential and strong phylogenetic signal, in the current study we examine feathers subjected to different burial environments for a duration of ~10 years, using transmission electron microscopy (TEM) and in situ immunofluorescence (IF). We use morphology and persistence of specific immunoreactivity as indicators of preservation at the molecular and microstructural levels. We show that feather keratin is durable, demonstrates structural and microstructural integrity, and retains epitopes suitable for specific antibody recognition in even the harshest conditions. These data support the hypothesis that keratin antibody reactivity can be used to identify the nature and composition of epidermal structures in the rock record, and to address evolutionary questions by distinguishing between alpha- (widely distributed) and beta- (limited to sauropsids) keratin. PMID:27384819

  7. MicroRNAs resolve an apparent conflict between annelid systematics and their fossil record

    PubMed Central

    Sperling, Erik A.; Vinther, Jakob; Moy, Vanessa N.; Wheeler, Benjamin M.; Sémon, Marie; Briggs, Derek E. G.; Peterson, Kevin J.

    2009-01-01

    Both the monophyly and inter-relationships of the major annelid groups have remained uncertain, despite intensive research on both morphology and molecular sequences. Morphological cladistic analyses indicate that Annelida is monophyletic and consists of two monophyletic groups, the clitellates and polychaetes, whereas molecular phylogenetic analyses suggest that polychaetes are paraphyletic and that sipunculans are crown-group annelids. Both the monophyly of polychaetes and the placement of sipunculans within annelids are in conflict with the annelid fossil record—the former because Cambrian stem taxa are similar to modern polychaetes in possessing biramous parapodia, suggesting that clitellates are derived from polychaetes; the latter because although fossil sipunculans are known from the Early Cambrian, crown-group annelids do not appear until the latest Cambrian. Here we apply a different data source, the presence versus absence of specific microRNAs—genes that encode approximately 22 nucleotide non-coding regulatory RNAs—to the problem of annelid phylogenetics. We show that annelids are monophyletic with respect to sipunculans, and polychaetes are paraphyletic with respect to the clitellate Lumbricus, conclusions that are consistent with the fossil record. Further, sipunculans resolve as the sister group of the annelids, rooting the annelid tree, and revealing the polarity of the morphological change within this diverse lineage of animals. PMID:19755470

  8. First Quaternary Fossil Record of Caecilians from a Mexican Archaeological Site

    NASA Astrophysics Data System (ADS)

    Wake, Thomas A.; Wake, Marvalee H.; Lesure, Richard G.

    1999-07-01

    A single vertebra from an Early Formative period archaeological site in coastal Chiapas, México, is identified as belonging to the amphibian Dermophis mexicanus (Duméril and Bibron) 1841 (Amphibia: Gymnophiona: Caeciliidae). The vertebra was recovered from deposits dated to approximately 1200-1350 B.C. The specimen represents the first Quaternary fossil record for gymnophiones. Its presence suggests the possible role of the species as a bioturbator. Its recovery is further evidence of the utility of fine-grained archaeological recovery techniques.

  9. Preservation of key biomolecules in the fossil record: current knowledge and future challenges.

    PubMed Central

    Bada, J L; Wang, X S; Hamilton, H

    1999-01-01

    preservation in the fossil record. PMID:10091249

  10. Evolutionary timescale of monocots determined by the fossilized birth-death model using a large number of fossil records.

    PubMed

    Eguchi, Satoshi; Tamura, Minoru N

    2016-05-01

    Although the phylogenetic relationships between monocot orders are sufficiently understood, a timescale of their evolution is needed. Several studies on molecular clock dating are available, but their results have been biased by their calibration schemes. Recently, the fossilized birth-death model, a type of Bayesian dating method, was proposed, and it does not require prior calibration and allows the use all available fossils. Using this model, we conducted divergence-time estimations of monocots to explore their evolutionary timeline without calibration bias. This is the first application of this model to seed plants. The dataset contained the matK and rbcL chloroplast genes of 118 monocot genera covering all extant orders. We employed information from 247 monocot fossils, which exceeded previous dating analyses that used a maximum of 12 monocot fossils. The crown group of monocots was dated to approximately the Late Jurassic-Early Cretaceous periods, and most extant monocot orders were estimated to diverge throughout the Early Cretaceous. Our results overlapped with the divergence time of insect lineages, such as beetles and flies, suggesting an association with pollinators in early monocot evolution. In addition, we proposed three new orders based on divergence time: Orchidales separated from Asparagales and Tofieldiales and Arales separated from Aslimatales. PMID:27061096

  11. Microbial fossil record of rocks from the Ross Desert, Antarctica: implications in the search for past life on Mars

    NASA Astrophysics Data System (ADS)

    Wierzchos, Jacek; Ascaso, Carmen

    2002-01-01

    Cryptoendolithic microbial communities living within Antarctic rocks are an example of survival in an extremely cold and dry environment. The extinction of these micro-organisms formerly colonizing sandstone in the Mount Fleming area (Ross Desert), was probably provoked by the hostile environment. This is considered to be a good terrestrial analogue of the first stage of the disappearance of possible life on early Mars. To date, only macroscopically observed indirect biomarkers of the past activity of cryptoendoliths in Antarctic rocks have been described. The present paper confirms, for the first time, the existence of cryptoendolith microbial fossils within these sandstone rocks. The novel in situ application of scanning electron microscopy with backscattered electron imaging and simultaneous use of X-ray energy dispersive spectroscopy allowed the clear detection of microfossils left behind by Antarctic endoliths. Careful interpretation of the morphological features of cells, such as preserved cell walls in algae, fungi and bacteria, cytoplasm elements such as chloroplast membranes in algae and organic matter traces, mineral associations, and the spatial context of these structures all point to their identification as cryptoendolith microfossils. This type of investigation will prompt the development of research strategies aimed at locating and identifying the signs that Martian microbiota, probably only bacteria if they existed, may have been left for us to see.

  12. 2015 Antarctic Maximum Sea Ice Extent Breaks Streak of Record Highs

    NASA Video Gallery

    Antarctic sea ice likely reached its annual maximum extent on Oct. 6, barring a late season surge. This video shows the evolution of the sea ice cover of the Southern Ocean from its minimum yearly ...

  13. Relict endemism of extant Rhineuridae (Amphisbaenia): testing for phylogenetic niche conservatism in the fossil record.

    PubMed

    Hipsley, Christy A; Müller, Johannes

    2014-03-01

    Rhineurid amphisbaenians are represented by a rich Cenozoic fossil record in North America, but today conisist of a single living species restricted to the Florida Peninsula. Such relict endemism may be the result of phylogenetic niche conservatism (PNC), the retention of ancestral traits preventing expansion into new environments. Most tests of PNC derive ancestral niche preferences from species' extant ecologies, while ignoring valuable paleontological information. To test if PNC contributes to the restricted distribution of modern Rhineura floridana, we compare the species' current environmental preferences (temperature, precipitation and soil) to paleoenvironmental data from the rhineurid fossil record. We find no evidence of PNC in modern R. floridana, as it also occurred in Florida during drier glacial periods. Ancient rhineurids also exhibit tolerance to changing climates, having undergone a shift from subtropical-humid to semi-arid savanna conditions during the Eocene-Oligocene transition. However, rhineurids nearly disappear from North America after the middle Miocene, potentially due to the onset of prolonged freezing temperatures following the mid-Miocene Climatic Optimum. This physiological limit of environmental tolerances could be interpreted as PNC for the entire family, but also characterizes much of Amphisbaenia, emphasizing the relevance of the temporal as well as phylogenetic scale at which PNC is investigated. PMID:24482295

  14. Biology in the Anthropocene: Challenges and insights from young fossil records.

    PubMed

    Kidwell, Susan M

    2015-04-21

    With overwhelming evidence of change in habitats, biologists today must assume that few, if any, study areas are natural and that biological variability is superimposed on trends rather than stationary means. Paleobiological data from the youngest sedimentary record, including death assemblages actively accumulating on modern land surfaces and seabeds, provide unique information on the status of present-day species, communities, and biomes over the last few decades to millennia and on their responses to natural and anthropogenic environmental change. Key advances have established the accuracy and resolving power of paleobiological information derived from naturally preserved remains and of proxy evidence for environmental conditions and sample age so that fossil data can both implicate and exonerate human stressors as the drivers of biotic change and permit the effects of multiple stressors to be disentangled. Legacy effects from Industrial and even pre-Industrial anthropogenic extirpations, introductions, (de)nutrification, and habitat conversion commonly emerge as the primary factors underlying the present-day status of populations and communities; within the last 2 million years, climate change has rarely been sufficient to drive major extinction pulses absent other human pressures, which are now manifold. Young fossil records also provide rigorous access to the baseline composition and dynamics of modern-day biota under pre-Industrial conditions, where insights include the millennial-scale persistence of community structures, the dominant role of physical environmental conditions rather than biotic interactions in determining community composition and disassembly, and the existence of naturally alternating states. PMID:25901315

  15. Changes to the Fossil Record of Insects through Fifteen Years of Discovery.

    PubMed

    Nicholson, David B; Mayhew, Peter J; Ross, Andrew J

    2015-01-01

    The first and last occurrences of hexapod families in the fossil record are compiled from publications up to end-2009. The major features of these data are compared with those of previous datasets (1993 and 1994). About a third of families (>400) are new to the fossil record since 1994, over half of the earlier, existing families have experienced changes in their known stratigraphic range and only about ten percent have unchanged ranges. Despite these significant additions to knowledge, the broad pattern of described richness through time remains similar, with described richness increasing steadily through geological history and a shift in dominant taxa, from Palaeoptera and Polyneoptera to Paraneoptera and Holometabola, after the Palaeozoic. However, after detrending, described richness is not well correlated with the earlier datasets, indicating significant changes in shorter-term patterns. There is reduced Palaeozoic richness, peaking at a different time, and a less pronounced Permian decline. A pronounced Triassic peak and decline is shown, and the plateau from the mid Early Cretaceous to the end of the period remains, albeit at substantially higher richness compared to earlier datasets. Origination and extinction rates are broadly similar to before, with a broad decline in both through time but episodic peaks, including end-Permian turnover. Origination more consistently exceeds extinction compared to previous datasets and exceptions are mainly in the Palaeozoic. These changes suggest that some inferences about causal mechanisms in insect macroevolution are likely to differ as well. PMID:26176667

  16. Biology in the Anthropocene: Challenges and insights from young fossil records

    PubMed Central

    Kidwell, Susan M.

    2015-01-01

    With overwhelming evidence of change in habitats, biologists today must assume that few, if any, study areas are natural and that biological variability is superimposed on trends rather than stationary means. Paleobiological data from the youngest sedimentary record, including death assemblages actively accumulating on modern land surfaces and seabeds, provide unique information on the status of present-day species, communities, and biomes over the last few decades to millennia and on their responses to natural and anthropogenic environmental change. Key advances have established the accuracy and resolving power of paleobiological information derived from naturally preserved remains and of proxy evidence for environmental conditions and sample age so that fossil data can both implicate and exonerate human stressors as the drivers of biotic change and permit the effects of multiple stressors to be disentangled. Legacy effects from Industrial and even pre-Industrial anthropogenic extirpations, introductions, (de)nutrification, and habitat conversion commonly emerge as the primary factors underlying the present-day status of populations and communities; within the last 2 million years, climate change has rarely been sufficient to drive major extinction pulses absent other human pressures, which are now manifold. Young fossil records also provide rigorous access to the baseline composition and dynamics of modern-day biota under pre-Industrial conditions, where insights include the millennial-scale persistence of community structures, the dominant role of physical environmental conditions rather than biotic interactions in determining community composition and disassembly, and the existence of naturally alternating states. PMID:25901315

  17. Changes to the Fossil Record of Insects through Fifteen Years of Discovery

    PubMed Central

    Nicholson, David B.; Mayhew, Peter J.; Ross, Andrew J.

    2015-01-01

    The first and last occurrences of hexapod families in the fossil record are compiled from publications up to end-2009. The major features of these data are compared with those of previous datasets (1993 and 1994). About a third of families (>400) are new to the fossil record since 1994, over half of the earlier, existing families have experienced changes in their known stratigraphic range and only about ten percent have unchanged ranges. Despite these significant additions to knowledge, the broad pattern of described richness through time remains similar, with described richness increasing steadily through geological history and a shift in dominant taxa, from Palaeoptera and Polyneoptera to Paraneoptera and Holometabola, after the Palaeozoic. However, after detrending, described richness is not well correlated with the earlier datasets, indicating significant changes in shorter-term patterns. There is reduced Palaeozoic richness, peaking at a different time, and a less pronounced Permian decline. A pronounced Triassic peak and decline is shown, and the plateau from the mid Early Cretaceous to the end of the period remains, albeit at substantially higher richness compared to earlier datasets. Origination and extinction rates are broadly similar to before, with a broad decline in both through time but episodic peaks, including end-Permian turnover. Origination more consistently exceeds extinction compared to previous datasets and exceptions are mainly in the Palaeozoic. These changes suggest that some inferences about causal mechanisms in insect macroevolution are likely to differ as well. PMID:26176667

  18. First direct evidence of a vertebrate three-level trophic chain in the fossil record.

    PubMed

    Kriwet, Jürgen; Witzmann, Florian; Klug, Stefanie; Heidtke, Ulrich H J

    2008-01-22

    We describe the first known occurrence of a Permian shark specimen preserving two temnospondyl amphibians in its digestive tract as well as the remains of an acanthodian fish, which was ingested by one of the temnospondyls. This exceptional find provides for the first time direct evidence of a vertebrate three-level food chain in the fossil record with the simultaneous preservation of three trophic levels. Our analysis shows that small-sized Lower Permian xenacanthid sharks of the genus Triodus preyed on larval piscivorous amphibians. The recorded trophic interaction can be explained by the adaptation of certain xenacanthids to fully freshwater environments and the fact that in these same environments, large temnospondyls occupied the niche of modern crocodiles. This unique faunal association has not been documented after the Permian and Triassic. Therefore, this Palaeozoic three-level food chain provides strong and independent support for changes in aquatic trophic chain structures through time. PMID:17971323

  19. Seismic stratigraphy of the East Antarctic margin: a record of Cenozoic environmental changes

    NASA Astrophysics Data System (ADS)

    Leychenkov, German; Guseva, Julia

    2010-05-01

    We have analyzed more than 120000 km of MCS sections collected on the East Antarctic margin (EAM) from 7E to 142E to correlate seismic stratigraphy with Antarctic glacial history predicted from drilling data and deep-sea proxy records, and to estimate what sort of information about ice sheet behavior and paleoceanographic conditions is contained in seismic records. Most of analyzed MCS lines are located on the continental rise and only the Prydz Bay (PB) shelf was studied in details. Five mayor horizons numbered up-section from "1" to "5" are identified in sedimentary cover of deep water EAM (continental rise). Horizon "1" and "2" are correlated with asynchronous Gondwana breakup and early post-breakup events, respectively; horizons "3", "4" and "5" are proposed to be isochronous surfaces related to Late Cenozoic paleoenvironmental transitions. The distinguishing feature of EAM sedimentary cover is the clear upward change in reflection pattern across horizons "3" and "4" that separates a lower sedimentary unit with mostly parallel reflectors from an upper one consisting of variety of acoustic facies typical of active down-slope and along slope processes. This change is associated with the arrival of the ice sheet to the Antarctic margin and significant increase in sedimentary input to deep water regions. Major results of our study are following: 1) Widespread development of channel-levee systems and other facies related to mass-wasting on the EAM is observed above horizon "4" and this interface is proposed to mark continental-scale Antarctic glaciation in the Early Oligocene. However, earliest signs of active down-slope processes are revealed on the Wilkes Land margin (WLM) above horizon "3" and we infer that this margin was glaciated first, probably in the Late Eocene. Under the temperate climate condition debris was delivered to the slope and rise by glaciers (which flowed from central Antarctica via Aurora Subglacial Basin) and abundant melt-water. The rate of

  20. Molecular decay of the tooth gene Enamelin (ENAM) mirrors the loss of enamel in the fossil record of placental mammals.

    PubMed

    Meredith, Robert W; Gatesy, John; Murphy, William J; Ryder, Oliver A; Springer, Mark S

    2009-09-01

    Vestigial structures occur at both the anatomical and molecular levels, but studies documenting the co-occurrence of morphological degeneration in the fossil record and molecular decay in the genome are rare. Here, we use morphology, the fossil record, and phylogenetics to predict the occurrence of "molecular fossils" of the enamelin (ENAM) gene in four different orders of placental mammals (Tubulidentata, Pholidota, Cetacea, Xenarthra) with toothless and/or enamelless taxa. Our results support the "molecular fossil" hypothesis and demonstrate the occurrence of frameshift mutations and/or stop codons in all toothless and enamelless taxa. We then use a novel method based on selection intensity estimates for codons (omega) to calculate the timing of iterated enamel loss in the fossil record of aardvarks and pangolins, and further show that the molecular evolutionary history of ENAM predicts the occurrence of enamel in basal representatives of Xenarthra (sloths, anteaters, armadillos) even though frameshift mutations are ubiquitous in ENAM sequences of living xenarthrans. The molecular decay of ENAM parallels the morphological degeneration of enamel in the fossil record of placental mammals and provides manifest evidence for the predictive power of Darwin's theory. PMID:19730686

  1. Calcification and silicification: fossilization potential of cyanobacteria from stromatolites of Niuafo'ou's Caldera Lakes (Tonga) and implications for the early fossil record.

    PubMed

    Kremer, Barbara; Kazmierczak, Józef; Lukomska-Kowalczyk, Maja; Kempe, Stephan

    2012-06-01

    Calcification and silicification processes of cyanobacterial mats that form stromatolites in two caldera lakes of Niuafo'ou Island (Vai Lahi and Vai Si'i) were evaluated, and their importance as analogues for interpreting the early fossil record are discussed. It has been shown that the potential for morphological preservation of Niuafo'ou cyanobacteria is highly dependent on the timing and type of mineral phase involved in the fossilization process. Four main modes of mineralization of cyanobacteria organic parts have been recognized: (i) primary early postmortem calcification by aragonite nanograins that transform quickly into larger needle-like crystals and almost totally destroy the cellular structures, (ii) primary early postmortem silicification of almost intact cyanobacterial cells that leave a record of spectacularly well-preserved cellular structures, (iii) replacement by silica of primary aragonite that has already recrystallized and obliterated the cellular structures, (iv) occasional replacement of primary aragonite precipitated in the mucopolysaccharide sheaths and extracellular polymeric substances by Al-Mg-Fe silicates. These observations suggest that the extremely scarce earliest fossil record may, in part, be the result of (a) secondary replacement by silica of primary carbonate minerals (aragonite, calcite, siderite), which, due to recrystallization, had already annihilated the cellular morphology of the mineralized microbiota or (b) relatively late primary silicification of already highly degraded and no longer morphologically identifiable microbial remains. PMID:22794297

  2. Calcification and Silicification: Fossilization Potential of Cyanobacteria from Stromatolites of Niuafo‘ou's Caldera Lakes (Tonga) and Implications for the Early Fossil Record

    PubMed Central

    Kazmierczak, Józef; Łukomska-Kowalczyk, Maja; Kempe, Stephan

    2012-01-01

    Abstract Calcification and silicification processes of cyanobacterial mats that form stromatolites in two caldera lakes of Niuafo‘ou Island (Vai Lahi and Vai Si‘i) were evaluated, and their importance as analogues for interpreting the early fossil record are discussed. It has been shown that the potential for morphological preservation of Niuafo‘ou cyanobacteria is highly dependent on the timing and type of mineral phase involved in the fossilization process. Four main modes of mineralization of cyanobacteria organic parts have been recognized: (i) primary early postmortem calcification by aragonite nanograins that transform quickly into larger needle-like crystals and almost totally destroy the cellular structures, (ii) primary early postmortem silicification of almost intact cyanobacterial cells that leave a record of spectacularly well-preserved cellular structures, (iii) replacement by silica of primary aragonite that has already recrystallized and obliterated the cellular structures, (iv) occasional replacement of primary aragonite precipitated in the mucopolysaccharide sheaths and extracellular polymeric substances by Al-Mg-Fe silicates. These observations suggest that the extremely scarce earliest fossil record may, in part, be the result of (a) secondary replacement by silica of primary carbonate minerals (aragonite, calcite, siderite), which, due to recrystallization, had already annihilated the cellular morphology of the mineralized microbiota or (b) relatively late primary silicification of already highly degraded and no longer morphologically identifiable microbial remains. Key Words: Stromatolites—Cyanobacteria—Calcification—Silicification—Niuafo‘ou (Tonga)—Archean. Astrobiology 12, 535–548. PMID:22794297

  3. A 300-million-year record of atmospheric carbon dioxide from fossil plant cuticles

    NASA Astrophysics Data System (ADS)

    Retallack, Gregory J.

    2001-05-01

    To understand better the link between atmospheric CO2 concentrations and climate over geological time, records of past CO2 are reconstructed from geochemical proxies. Although these records have provided us with a broad picture of CO2 variation throughout the Phanerozoic eon (the past 544Myr), inconsistencies and gaps remain that still need to be resolved. Here I present a continuous 300-Myr record of stomatal abundance from fossil leaves of four genera of plants that are closely related to the present-day Ginkgo tree. Using the known relationship between leaf stomatal abundance and growing season CO2 concentrations, I reconstruct past atmospheric CO2 concentrations. For the past 300Myr, only two intervals of low CO2 (<1,000p.p.m.v.) are inferred, both of which coincide with known ice ages in Neogene (1-8Myr) and early Permian (275-290Myr) times. But for most of the Mesozoic era (65-250Myr), CO2 levels were high (1,000-2,000p.p.m.v.), with transient excursions to even higher CO2 (>2,000p.p.m.v.) concentrations. These results are consistent with some reconstructions of past CO2 (refs 1, 2) and palaeotemperature records, but suggest that CO2 reconstructions based on carbon isotope proxies may be compromised by episodic outbursts of isotopically light methane. These results support the role of water vapour, methane and CO2 in greenhouse climate warming over the past 300Myr.

  4. A 300-million-year record of atmospheric carbon dioxide from fossil plant cuticles.

    PubMed

    Retallack, G J

    2001-05-17

    To understand better the link between atmospheric CO2 concentrations and climate over geological time, records of past CO2 are reconstructed from geochemical proxies. Although these records have provided us with a broad picture of CO2 variation throughout the Phanerozoic eon (the past 544 Myr), inconsistencies and gaps remain that still need to be resolved. Here I present a continuous 300-Myr record of stomatal abundance from fossil leaves of four genera of plants that are closely related to the present-day Ginkgo tree. Using the known relationship between leaf stomatal abundance and growing season CO2 concentrations, I reconstruct past atmospheric CO2 concentrations. For the past 300 Myr, only two intervals of low CO2 (<1,000 p.p.m.v.) are inferred, both of which coincide with known ice ages in Neogene (1-8 Myr) and early Permian (275-290 Myr) times. But for most of the Mesozoic era (65-250 Myr), CO2 levels were high (1,000-2,000 p.p.m.v.), with transient excursions to even higher CO2 (>2,000 p.p.m.v.) concentrations. These results are consistent with some reconstructions of past CO2 (refs 1, 2) and palaeotemperature records, but suggest that CO2 reconstructions based on carbon isotope proxies may be compromised by episodic outbursts of isotopically light methane. These results support the role of water vapour, methane and CO2 in greenhouse climate warming over the past 300 Myr. PMID:11357126

  5. A Late Miocene-Pliocene Antarctic Deepwater Record of Cyclic Iron Reduction Events (ODP Leg 178 Site 1095)

    NASA Astrophysics Data System (ADS)

    Hepp, D. A.; Moerz, T.

    2007-12-01

    The Pacific margin off the Antarctic Peninsula is very sensitive to climate and ice-sheet volume changes. Climatic variations on the continental shelf control regional sedimentary processes and foster the build-up of giant deep- sea sediment drifts. These drifts represent the most proximal continuous sedimentary recorders for West Antarctic ice sheet evolution and glacial-interglacial cyclicity pattern. Sediment physical, geochemical records and x-ray images derived from ODP Site 1095 (Drift 7) were used to identify pattern in glacial-interglacial cyclicity and associated sedimentary and diagenetic processes during late Miocene and Pliocene. Two boundary types dividing half-cycles have been recognized: (1) interglacial-to-glacial transitions are characterized by a sharp boundary and abrupt change in lithology; (2) glacial-to-interglacial transitions can described as a gradual change from a full glacial to a full interglacial stage. A prominent feature of the glacial-to-interglacial transition is the loss of the magnetic susceptibility signal, caused by diagenetic alteration and demagnetization of magnetic iron minerals in a suboxic to anoxic sediment environment. Similar redox processes are described for organic carbon rich Madeira abyssal plain turbidites and Mediterranean sapropels, but are uncommon for vented Circum- Antarctic deep-sea sediments. Iron reduction zones were coupled to the ice sheet collapse at the end of deglaciation phases. Ice sheet collapse and meltwater formation weaken the bottom water formation and convection, but foster short living diatom blooms resulting in high fluxes of organic matter to the seafloor. Iron reduction zones were observed in sixty-four zones of ODP Site 1095 cores. Thus, the sedimentary record of Drift 7 affords an unique opportunity to study cyclic iron reduction events at long time-scales. The occurrence and intensity of those 'diagenetic zones' reflect long-term trends of global climate change and the related

  6. The taphonomy of unmineralised Palaeozoic fossils preserved as siliciclastic moulds and casts, and their utility in assessing the interaction between environmental change and the fossil record

    NASA Astrophysics Data System (ADS)

    MacGabhann, Breandán; Schiffbauer, James; Hagadorn, James; Van Roy, Peter; Lynch, Edward; Morrsion, Liam; Murray, John

    2015-04-01

    biopolymers, and that these tissues were preferentially fossilised by the formation of an early diagenic mould directly on the organic surfaces. Excess divalent iron ions, produced during decay of more labile tissues by means of bacterial iron reduction, would have adsorbed to anionic functional groups in the biopolymeric tissues. This would have provided a ready substrate for the formation and growth of such an early diagenic mineralised mould, including aluminosilicate minerals produced via reaction with seawater silica and metal ions, and iron sulphide minerals produced via reaction with hydrogen sulphide and free sulphur produced from seawater sulphate through bacterial sulphate reduction associated with further decay. Subsequent weathering would have oxidised such iron sulphides to oxides and oxyhydroxides. This taphonomic model supports the lack of utility of the eldonid palaeobiological record in analysing environmental influence on biological communities, due to the lack of preservation of key anatomical components. However, it also suggests that the very occurrence of fossils preserved in this style is dependent on extrinsic palaeoenvironmental factors - including pH, Eh, and the concentration of other ions in the contemporaneous seawater. Analyses of the distribution of fossils preserved in this style may therefore provide information on ambient conditions which may have affected the distribution of contemporaneous mineralised fossils, potentially allowing a more complete analysis of the effects of palaeoenvironmental change on fossil ecosystems.

  7. 'Unlocking the archive': Using photogrammetry of historic aerial photographs to extend the record of glacier change on the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Clarke, Lucy; Fox, Adrian

    2014-05-01

    associated errors using an example glacier from the Antarctic Peninsula to highlight the suitability of this technique and demonstrate the data that can be obtained. The photogrammetric technique that is being employed for this research allows accurate measurements of surface elevation change on glaciers on the Antarctic Peninsula over a 50 year-time span, enabling both spatial and temporal patterns of change and improving understanding of glacier response in this area. The use of this technique opens up possibilities for 'unlocking the archive' in other remote glacial areas where historic aerial photography exists but the collection of ground control points is limited. References: Fox, A. J. and Cziferszky, A. 2008. Unlocking the time capsule of historic aerial photography to measure changes in Antarctic Peninsula glaciers. Photogrammetric Record, 23 (121): 51-68. Hock, R., de Woul, M., Radic, V. and Dyurgerov, M. 2009. Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution. Geophysical Research Letters, 36, L07501.

  8. Balsscallichirus Sakai, 2011 (Decapoda: Axiidea: Callianassidae) in the fossil record: systematics and palaeobiogeography

    PubMed Central

    Hyžný, Matúš

    2016-01-01

    The fossil record of the ghost shrimp genus Balsscallichirus Sakai, 2011 (Crustacea: Decapoda: Callianassidae) is revised. Barnardcallichirus Sakai, 2011 and Tirmizicallichirus Sakai, 2011 are considered subjective synonyms of Balsscallichirus. Based on the examination of extant species it is argued that the morphology of the major cheliped merus, in combination with other hard part morphology characters, is sufficient for assignment of the fossil material into the genus. Main identifying characters are on merus which is keeled along its midline and its lower half is tuberculated; its lower margin possesses broad proximal meral hook continuing into a lobe distally; the entire lower margin is subdivided into numerous irregularly spaced spines. Three species, Callianassa sismondai A. Milne-Edwards, 1860, C. floriana Glaessner, 1928, and Podocallichirus laepaensis Hyžný & Muñiz, 2012, originally described from the Miocene of Italy, Austria and Spain, respectively, are assigned to Balsscallichirus herein. Neocallichirus wellsi Schweitzer, Feldmann & Gingerich, 2004 from the Upper Eocene of Pakistan is tentatively assigned to that genus as well. Spatial and temporal distribution of the genus indicates that at least since the Oligocene, and possibly even sooner (the Late Eocene), the genus has been restricted to the Western Tethys Region. Later, it migrated also into West Atlantic establishing present day communities. PMID:27499568

  9. An ecometric analysis of the fossil mammal record of the Turkana Basin

    PubMed Central

    Žliobaitė, Indrė; Kaya, Ferhat; Bibi, Faysal; Bobe, René; Leakey, Louise; Leakey, Meave; Patterson, David; Rannikko, Janina; Werdelin, Lars

    2016-01-01

    Although ecometric methods have been used to analyse fossil mammal faunas and environments of Eurasia and North America, such methods have not yet been applied to the rich fossil mammal record of eastern Africa. Here we report results from analysis of a combined dataset spanning east and west Turkana from Kenya between 7 and 1 million years ago (Ma). We provide temporally and spatially resolved estimates of temperature and precipitation and discuss their relationship to patterns of faunal change, and propose a new hypothesis to explain the lack of a temperature trend. We suggest that the regionally arid Turkana Basin may between 4 and 2 Ma have acted as a ‘species factory’, generating ecological adaptations in advance of the global trend. We show a persistent difference between the eastern and western sides of the Turkana Basin and suggest that the wetlands of the shallow eastern side could have provided additional humidity to the terrestrial ecosystems. Pending further research, a transient episode of faunal change centred at the time of the KBS Member (1.87–1.53 Ma), may be equally plausibly attributed to climate change or to a top-down ecological cascade initiated by the entry of technologically sophisticated humans. This article is part of the themed issue ‘Major transitions in human evolution’. PMID:27298463

  10. An ecometric analysis of the fossil mammal record of the Turkana Basin.

    PubMed

    Fortelius, Mikael; Žliobaitė, Indrė; Kaya, Ferhat; Bibi, Faysal; Bobe, René; Leakey, Louise; Leakey, Meave; Patterson, David; Rannikko, Janina; Werdelin, Lars

    2016-07-01

    Although ecometric methods have been used to analyse fossil mammal faunas and environments of Eurasia and North America, such methods have not yet been applied to the rich fossil mammal record of eastern Africa. Here we report results from analysis of a combined dataset spanning east and west Turkana from Kenya between 7 and 1 million years ago (Ma). We provide temporally and spatially resolved estimates of temperature and precipitation and discuss their relationship to patterns of faunal change, and propose a new hypothesis to explain the lack of a temperature trend. We suggest that the regionally arid Turkana Basin may between 4 and 2 Ma have acted as a 'species factory', generating ecological adaptations in advance of the global trend. We show a persistent difference between the eastern and western sides of the Turkana Basin and suggest that the wetlands of the shallow eastern side could have provided additional humidity to the terrestrial ecosystems. Pending further research, a transient episode of faunal change centred at the time of the KBS Member (1.87-1.53 Ma), may be equally plausibly attributed to climate change or to a top-down ecological cascade initiated by the entry of technologically sophisticated humans.This article is part of the themed issue 'Major transitions in human evolution'. PMID:27298463

  11. New Biogeographic insight into Bauhinia s.l. (Leguminosae): integration from fossil records and molecular analyses

    PubMed Central

    2014-01-01

    Background Given that most species that have ever existed on earth are extinct, it stands to reason that the evolutionary history can be better understood with fossil taxa. Bauhinia is a typical genus of pantropical intercontinental disjunction among the Asian, African, and American continents. Geographic distribution patterns are better recognized when fossil records and molecular sequences are combined in the analyses. Here, we describe a new macrofossil species of Bauhinia from the Upper Miocene Xiaolongtan Formation in Wenshan County, Southeast Yunnan, China, and elucidate the biogeographic significance through the analyses of molecules and fossils. Results Morphometric analysis demonstrates that the leaf shapes of B. acuminata, B. championii, B. chalcophylla, B. purpurea, and B. podopetala closely resemble the leaf shapes of the new finding fossil. Phylogenetic relationships among the Bauhinia species were reconstructed using maximum parsimony and Bayesian inference, which inferred that species in Bauhinia species are well-resolved into three main groups. Divergence times were estimated by the Bayesian Markov chain Monte Carlo (MCMC) method under a relaxed clock, and inferred that the stem diversification time of Bauhinia was ca. 62.7 Ma. The Asian lineage first diverged at ca. 59.8 Ma, followed by divergence of the Africa lineage starting during the late Eocene, whereas that of the neotropical lineage starting during the middle Miocene. Conclusions Hypotheses relying on vicariance or continental history to explain pantropical disjunct distributions are dismissed because they require mostly Palaeogene and older tectonic events. We suggest that Bauhinia originated in the middle Paleocene in Laurasia, probably in Asia, implying a possible Tethys Seaway origin or an “Out of Tropical Asia”, and dispersal of legumes. Its present pantropical disjunction resulted from disruption of the boreotropical flora by climatic cooling after the Paleocene-Eocene Thermal

  12. A dinosaurian facial deformity and the first occurrence of ameloblastoma in the fossil record

    PubMed Central

    Dumbravă, Mihai D.; Rothschild, Bruce M.; Weishampel, David B.; Csiki-Sava, Zoltán; Andrei, Răzvan A.; Acheson, Katharine A.; Codrea, Vlad A.

    2016-01-01

    Despite documentation of various types of neoplastic pathologies encountered in the vertebrate fossil record, no ameloblastic tumours have been recognised so far. Ameloblastoma is a benign neoplasic tumour with a strong preponderance for the mandible. Here, we report for the first time the presence of an ameloblastoma neoplasm in the lower jaw of a specimen referred to the derived non-hadrosaurid hadrosauroid dinosaur Telmatosaurus transsylvanicus from the uppermost Cretaceous of the Haeg Basin in Romania. The location, external appearance and internal structure of the pathological outgrowth provide clear evidence for the diagnosis of ameloblastoma in Telmatosaurus. This report extends the range of pathologies encountered in hadrosauroid dinosaurs. In addition, recognition of an ameloblastoma neoplasm in a taxon lying close to the origin of ‘duck-billed’ hadrosaurid dinosaurs confirms the predisposition of this clade towards neoplasia pathologies already in its basal members. PMID:27377317

  13. A dinosaurian facial deformity and the first occurrence of ameloblastoma in the fossil record.

    PubMed

    Dumbravă, Mihai D; Rothschild, Bruce M; Weishampel, David B; Csiki-Sava, Zoltán; Andrei, Răzvan A; Acheson, Katharine A; Codrea, Vlad A

    2016-01-01

    Despite documentation of various types of neoplastic pathologies encountered in the vertebrate fossil record, no ameloblastic tumours have been recognised so far. Ameloblastoma is a benign neoplasic tumour with a strong preponderance for the mandible. Here, we report for the first time the presence of an ameloblastoma neoplasm in the lower jaw of a specimen referred to the derived non-hadrosaurid hadrosauroid dinosaur Telmatosaurus transsylvanicus from the uppermost Cretaceous of the Haeg Basin in Romania. The location, external appearance and internal structure of the pathological outgrowth provide clear evidence for the diagnosis of ameloblastoma in Telmatosaurus. This report extends the range of pathologies encountered in hadrosauroid dinosaurs. In addition, recognition of an ameloblastoma neoplasm in a taxon lying close to the origin of 'duck-billed' hadrosaurid dinosaurs confirms the predisposition of this clade towards neoplasia pathologies already in its basal members. PMID:27377317

  14. Extreme Glacial Legacies: A Synthesis of the Antarctic Springtail Phylogeographic Record

    PubMed Central

    McGaughran, Angela; Stevens, Mark I.; Hogg, Ian D.; Carapelli, Antonio

    2011-01-01

    We review current phylogeographic knowledge from across the Antarctic terrestrial landscape with a focus on springtail taxa. We describe consistent patterns of high genetic diversity and structure among populations which have persisted in glacial refugia across Antarctica over both short (<2 Mya) and long (>10 Mya) timescales. Despite a general concordance of results among species, we explain why location is important in determining population genetic patterns within bioregions. We complete our review by drawing attention to the main limitations in the field of Antarctic phylogeography, namely that the scope of geographic focus is often lacking within studies, and that large gaps remain in our phylogeographic knowledge for most terrestrial groups. PMID:26467614

  15. Fossil invertebrates records in cave sediments and paleoenvironmental assessments - a study of four cave sites from Romanian Carpathians

    NASA Astrophysics Data System (ADS)

    Moldovan, O. T.; Constantin, S.; Panaiotu, C.; Roban, R. D.; Frenzel, P.; Miko, L.

    2016-01-01

    Fossil invertebrates from cave sediments have been recently described as a potential new proxy for paleoenvironment and used in cross-correlations with alternate proxy records from cave deposits. Here we present the results of a fossil invertebrates study in four caves from two climatically different regions of the Romanian Carpathians, to complement paleoenvironmental data previously reported. Oribatid mites and ostracods are the most common invertebrates in the studied cave sediments. Some of the identified taxa are new to science, and most of them are indicative for either warm and/or cold stages or dry and/or wetter oscillations. In two caves the fossil invertebrates records indicate rapid climate oscillations during times known for a relatively stable climate. By corroborating the fossil invertebrates' record with the information given by magnetic properties and sediment structures, complementary data on past vegetation, temperatures and hydraulic regimes could be gathered. This paper analyzes the potential of fossil invertebrate records as a paleoenvironmental proxy, potential problems and pitfalls.

  16. Hominin cognitive evolution: identifying patterns and processes in the fossil and archaeological record

    PubMed Central

    Shultz, Susanne; Nelson, Emma; Dunbar, Robin I. M.

    2012-01-01

    As only limited insight into behaviour is available from the archaeological record, much of our understanding of historical changes in human cognition is restricted to identifying changes in brain size and architecture. Using both absolute and residual brain size estimates, we show that hominin brain evolution was likely to be the result of a mix of processes; punctuated changes at approximately 100 kya, 1 Mya and 1.8 Mya are supplemented by gradual within-lineage changes in Homo erectus and Homo sapiens sensu lato. While brain size increase in Homo in Africa is a gradual process, migration of hominins into Eurasia is associated with step changes at approximately 400 kya and approximately 100 kya. We then demonstrate that periods of rapid change in hominin brain size are not temporally associated with changes in environmental unpredictability or with long-term palaeoclimate trends. Thus, we argue that commonly used global sea level or Indian Ocean dust palaeoclimate records provide little evidence for either the variability selection or aridity hypotheses explaining changes in hominin brain size. Brain size change at approximately 100 kya is coincident with demographic change and the appearance of fully modern language. However, gaps remain in our understanding of the external pressures driving encephalization, which will only be filled by novel applications of the fossil, palaeoclimatic and archaeological records. PMID:22734056

  17. Origin of the Eumetazoa: testing ecological predictions of molecular clocks against the Proterozoic fossil record

    NASA Technical Reports Server (NTRS)

    Peterson, Kevin J.; Butterfield, Nicholas J.

    2005-01-01

    Molecular clocks have the potential to shed light on the timing of early metazoan divergences, but differing algorithms and calibration points yield conspicuously discordant results. We argue here that competing molecular clock hypotheses should be testable in the fossil record, on the principle that fundamentally new grades of animal organization will have ecosystem-wide impacts. Using a set of seven nuclear-encoded protein sequences, we demonstrate the paraphyly of Porifera and calculate sponge/eumetazoan and cnidarian/bilaterian divergence times by using both distance [minimum evolution (ME)] and maximum likelihood (ML) molecular clocks; ME brackets the appearance of Eumetazoa between 634 and 604 Ma, whereas ML suggests it was between 867 and 748 Ma. Significantly, the ME, but not the ML, estimate is coincident with a major regime change in the Proterozoic acritarch record, including: (i) disappearance of low-diversity, evolutionarily static, pre-Ediacaran acanthomorphs; (ii) radiation of the high-diversity, short-lived Doushantuo-Pertatataka microbiota; and (iii) an order-of-magnitude increase in evolutionary turnover rate. We interpret this turnover as a consequence of the novel ecological challenges accompanying the evolution of the eumetazoan nervous system and gut. Thus, the more readily preserved microfossil record provides positive evidence for the absence of pre-Ediacaran eumetazoans and strongly supports the veracity, and therefore more general application, of the ME molecular clock.

  18. New Eocene Coleoid (Cephalopoda) Diversity from Statolith Remains: Taxonomic Assignation, Fossil Record Analysis, and New Data for Calibrating Molecular Phylogenies

    PubMed Central

    Neige, Pascal; Lapierre, Hervé; Merle, Didier

    2016-01-01

    New coleoid cephalopods are described from statolith remains from the Middle Eocene (Middle Lutetian) of the Paris Basin. Fifteen fossil statoliths are identified and assigned to the Sepiidae (Sepia boletzkyi sp. nov.,? Sepia pira sp. nov.), Loliginidae (Loligo clarkei sp. nov.), and Ommastrephidae (genus indet.) families. The sediments containing these fossils indicate permanent aquatic settings in the infralittoral domain. These sediments range in age from 46 Mya to 43 Mya. Analysis of the fossil record of statoliths (from findings described here, together with a review of previously published data) indicates marked biases in our knowledge. Fossil statoliths are known from as far back as the Early Jurassic (199.3 to 190.8 Mya) but surprisingly, to the best of our knowledge, no record occurs in the Cretaceous. This is a “knowledge bias” and clearly calls for further studies. Finally, we attempt to compare findings described here with fossils previously used to constrain divergence and/or diversification ages of some coleoid subclades in molecular phylogenies. This comparison clearly indicates that the new records detailed here will challenge some estimated divergence times of coleoid cephalopod subclades. PMID:27192490

  19. New Eocene Coleoid (Cephalopoda) Diversity from Statolith Remains: Taxonomic Assignation, Fossil Record Analysis, and New Data for Calibrating Molecular Phylogenies.

    PubMed

    Neige, Pascal; Lapierre, Hervé; Merle, Didier

    2016-01-01

    New coleoid cephalopods are described from statolith remains from the Middle Eocene (Middle Lutetian) of the Paris Basin. Fifteen fossil statoliths are identified and assigned to the Sepiidae (Sepia boletzkyi sp. nov.,? Sepia pira sp. nov.), Loliginidae (Loligo clarkei sp. nov.), and Ommastrephidae (genus indet.) families. The sediments containing these fossils indicate permanent aquatic settings in the infralittoral domain. These sediments range in age from 46 Mya to 43 Mya. Analysis of the fossil record of statoliths (from findings described here, together with a review of previously published data) indicates marked biases in our knowledge. Fossil statoliths are known from as far back as the Early Jurassic (199.3 to 190.8 Mya) but surprisingly, to the best of our knowledge, no record occurs in the Cretaceous. This is a "knowledge bias" and clearly calls for further studies. Finally, we attempt to compare findings described here with fossils previously used to constrain divergence and/or diversification ages of some coleoid subclades in molecular phylogenies. This comparison clearly indicates that the new records detailed here will challenge some estimated divergence times of coleoid cephalopod subclades. PMID:27192490

  20. Cenozoic prograding sequences of the Antarctic continental margin: a record of glacio-eustatic and tectonic events

    USGS Publications Warehouse

    Cooper, A. K.; Barrett, P.J.; Hinz, K.; Traube, V.; Letichenkov, G.; Stagg, H.M.J.

    1991-01-01

    times, like today, by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge. Ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge, thereby creating troughmouth fans and sheet-like prograding sequences (i.e. type IA sequences). Numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the Antarctic Ice Sheet. The available drilling and seismic interpretations provide the following history: (1) Cenozoic ice sheets have existed in places near the continental shelf since middle to late Eocene time. (2) A grounded Antarctic ice sheet first expanded to the continental shelf edge, with probable overdeepening of the outer shelf, in late Eucene to early Oligocene time in Prydz Bay, possibly in early Miocene time in the Ross Sea, and at least by middle Miocene time in the Weddell Sea. (3) The relative amounts of shelf prograding and inferred ice-volume variations (and related sea-level changes) have increased since middle to late Miocene time in the eastern Ross Sea, Prydz Bay, and possibly Weddell Sea. Our analysis is preliminary. Further acoustic surveys and scientific drilling are needed to resolve the proximal Antarctic record of glacio-eustatic, climatic, and tectonic events recorded by the prograding sequences. ?? 1991.

  1. Recording of climate and diagenesis through sedimentary DNA and fossil pigments at Laguna Potrok Aike, Argentina

    NASA Astrophysics Data System (ADS)

    Vuillemin, Aurèle; Ariztegui, Daniel; Leavitt, Peter R.; Bunting, Lynda; The Pasado Science Team

    2016-04-01

    Aquatic sediments record past climatic conditions while providing a wide range of ecological niches for microorganisms. In theory, benthic microbial community composition should depend on environmental features and geochemical conditions of surrounding sediments, as well as ontogeny of the subsurface environment as sediment degraded. In principle, DNA in sediments should be composed of ancient and extant microbial elements persisting at different degrees of preservation, although to date few studies have quantified the relative influence of each factor in regulating final composition of total sedimentary DNA assemblage. Here geomicrobiological and phylogenetic analyses of a Patagonian maar lake were used to indicate that the different sedimentary microbial assemblages derive from specific lacustrine regimes during defined climatic periods. Two climatic intervals (Mid-Holocene, 5 ka BP; Last Glacial Maximum, 25 ka BP) whose sediments harbored active microbial populations were sampled for a comparative environmental study based on fossil pigments and 16S rRNA gene sequences. The genetic assemblage recovered from the Holocene record revealed a microbial community displaying metabolic complementarities that allowed prolonged degradation of organic matter to methane. The series of Archaea identified throughout the Holocene record indicated an age-related stratification of these populations brought on by environmental selection during early diagenesis. These characteristics were associated with sediments resulting from endorheic lake conditions and stable pelagic regime, high evaporative stress and concomitant high algal productivity. In contrast, sulphate-reducing bacteria and lithotrophic Archaea were predominant in sediments dated from the Last Glacial Maximum, in which pelagic clays alternated with fine volcanic material characteristic of a lake level highstand and freshwater conditions, but reduced water column productivity. Comparison of sedimentary DNA composition

  2. Two new fossil genera and species of Cerocephalinae (Hymenoptera, Chalcidoidea, Pteromalidae), including the first record from the Eocene

    PubMed Central

    Bläser, Marcel; Krogmann, Lars; Peters, Ralph S.

    2015-01-01

    Abstract Cerocephalinae (Chalcidoidea, Pteromalidae) is a small group of parasitoid wasps characterized by a number of derived diagnostic features. Their hosts are endophytic beetles. So far, 43 species of Cerocephalinae have been described, including one fossil species from the Miocene. In this study, we add two new genera and species from Baltic and Dominican amber to the fossil record. Tenuicornus dominicus gen. et sp. n. is the second genus described from Dominican amber, and Pteropilosa lailarabanorum gen. et sp. n., described from Baltic amber, represents the oldest record of the subfamily, pushing the minimum age of Cerocephalinae back to the Eocene. Diagnostic characters of both species are discussed in comparison with other Cerocephalinae. An updated key to extant and fossil Cerocephalinae is presented. PMID:26798296

  3. Testing the Molecular Clock Using the Best Fossil Record: Case Studies from the Planktic Foraminifera

    NASA Astrophysics Data System (ADS)

    Steel, B. A.; Kucera, M.; Darling, K.

    2004-12-01

    Criticism of molecular clock studies often centres on inadequate calibration and a perceived lack of correlation between reproductive isolation and recognisable morphological evolution. Since many major groups (e.g. birds, mammals, reptiles) have a poor fossil record, it is often difficult to test and refute these limitations. Planktic foraminifera represent an exception to this rule. Deep-sea sediments are super-abundant in foraminifera, and large numbers of specimens and occurrences are easily garnered from Ocean Drilling Programme cores. Planktic foraminifera therefore represent an ideal model group with which to test and refine molecular clock studies. Since the 1990AƒAøAøâ_sA¬Aøâ_zAøs, genetic sequences (principally 18S r-RNA) have been extracted from living planktic foraminifera, and a large genetic library has developed. Our study attempts to contextualise and test molecular data, particularly AƒAøAøâ_sA¬A<Å"molecular clockAƒAøAøâ_sA¬Aøâ_zAø dates, utilising material from two ODP cores (Site 926A (Atlantic) and 806 (Pacific), to examine the evolutionary history of two sibling-species complexes (Globigerinella siphonifera and Globigerinoides ruber, both common shallow-water species and both of considerable palaeoceanographic utility). Recent genetic studies have suggested that these two AƒAøAøâ_sA¬A<Å"super-speciesAƒAøAøâ_sA¬Aøâ_zAø in fact consist of a number of isolated forms, with contrasting ecologies and longevities, which in Recent and sub-Recent sediments can be distinguished either on the basis of pore ultrastructure (Gl. siphonifera) or test colouration (Gs. ruber). In both cases, molecular clock estimates are indicative of ancient (7-11 Ma) intra-species cryptic divergences, which seem to be considerably older than fossil dates. In particular, the calculated molecular split between the two forms of Gs. ruber (AƒAøAøâ_sA¬A<Å"whiteAƒAøAøâ_sA¬Aøâ_zAø and AƒAøAøâ_sA¬A<Å"pinkA

  4. Fossil spiders.

    PubMed

    Selden, Paul A; Penney, David

    2010-02-01

    Over the last three decades, the fossil record of spiders has increased from being previously biased towards Tertiary ambers and a few dubious earlier records, to one which reveals a much greater diversity in the Mesozoic, with many of the modern families present in that era, and with clearer evidence of the evolutionary history of the group. We here record the history of palaeoarachnology and the major breakthroughs which form the basis of studies on fossil spiders. Understanding the preservation and taphonomic history of spider fossils is crucial to interpretation of fossil spider morphology. We also review the more recent descriptions of fossil spiders and the effect these discoveries have had on the phylogenetic tree of spiders. We discuss some features of the evolutionary history of spiders and present ideas for future work. PMID:19961468

  5. Introducing Evolution to Non-Biology Majors via the Fossil Record: A Case Study from the Israeli High School System.

    ERIC Educational Resources Information Center

    Dodick, Jeff; Orion, Nir

    2003-01-01

    Discusses challenges faced in the teaching and learning of evolution. Presents a curricular program and a case study on evolutionary biology. Investigates students' conceptual knowledge after exposure to the program "From Dinosaurs to Darwin," which focuses on fossil records as evidence of evolution. (Contains 32 references.) (YDS)

  6. 30-Year Satellite Record Reveals Accelerated Arctic Sea Ice Loss, Antarctic Sea Ice Trend Reversal

    NASA Technical Reports Server (NTRS)

    Cavalieri, Donald J.; Parkinson, C. L.; Vinnikov, K. Y.

    2003-01-01

    Arctic sea ice extent decreased by 0.30 plus or minus 0.03 x 10(exp 6) square kilometers per decade from 1972 through 2002, but decreased by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per decade from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast to the Arctic, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased, with an overall 30-year trend of -0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent observed in the early 1970's.

  7. Fossilized spermatozoa preserved in a 50-Myr-old annelid cocoon from Antarctica

    PubMed Central

    Bomfleur, Benjamin; Mörs, Thomas; Ferraguti, Marco; Reguero, Marcelo A.; McLoughlin, Stephen

    2015-01-01

    The origin and evolution of clitellate annelids—earthworms, leeches and their relatives—is poorly understood, partly because body fossils of these delicate organisms are exceedingly rare. The distinctive egg cases (cocoons) of Clitellata, however, are relatively common in the fossil record, although their potential for phylogenetic studies has remained largely unexplored. Here, we report the remarkable discovery of fossilized spermatozoa preserved within the secreted wall layers of a 50-Myr-old clitellate cocoon from Antarctica, representing the oldest fossil animal sperm yet known. Sperm characters are highly informative for the classification of extant Annelida. The Antarctic fossil spermatozoa have several features that point to affinities with the peculiar, leech-like ‘crayfish worms' (Branchiobdellida). We anticipate that systematic surveys of cocoon fossils coupled with advances in non-destructive analytical methods may open a new window into the evolution of minute, soft-bodied life forms that are otherwise only rarely observed in the fossil record. PMID:26179804

  8. A NEW SPECIES OF DIAPHANA FROM BATHYAL DEPTHS IN THE WEDDELL SEA, ANTARCTICA AND FIRST RECORD OF DIAPHANA INFLATA (STREBEL, 1908) IN THE HIGH ANTARCTIC (GASTROPODA: OPISTHOBRANCHIA).

    PubMed

    Linse, KATRIN; SchiØtte, TOM

    2002-05-01

    Diaphana haini n.sp. is described from Antarctica. With a depth range from about 400 to 2100 m, D. haini is the second Antarctic species of this genus to extend into the deep sea, the other being D. inflata (Strebel, 1908). Phylogenetic analysis has allowed D. haini to be incorporated within Schiøtte's (1998) cladogram for this genus and, thereby clarify its historical zoogeography. A record of D. inflata from the Weddell Sea extends its known distribution range. The recorded geographic distribution now ranges from South Georgia to the Antarctic continent, and the depth range is extended considerably, from 252-310 m to 1645 m. PMID:12011240

  9. Piscivory in a Miocene Cetotheriidae of Peru: first record of fossilized stomach content for an extinct baleen-bearing whale

    NASA Astrophysics Data System (ADS)

    Collareta, Alberto; Landini, Walter; Lambert, Olivier; Post, Klaas; Tinelli, Chiara; Di Celma, Claudio; Panetta, Daniele; Tripodi, Maria; Salvadori, Piero A.; Caramella, Davide; Marchi, Damiano; Urbina, Mario; Bianucci, Giovanni

    2015-12-01

    Instead of teeth, modern mysticetes bear hair-fringed keratinous baleen plates that permit various bulk-filtering predation techniques (from subsurface skimming to lateral benthic suction and engulfment) devoted to various target prey (from small invertebrates to schooling fish). Current knowledge about the feeding ecology of extant cetaceans is revealed by stomach content analyses and observations of behavior. Unfortunately, no fossil stomach contents of ancient mysticetes have been described so far; the investigation of the diet of fossil baleen whales, including the Neogene family Cetotheriidae, remains thus largely speculative. We report on an aggregate of fossil fish remains found within a mysticete skeleton belonging to an undescribed late Miocene (Tortonian) cetotheriid from the Pisco Formation (Peru). Micro-computed tomography allowed us to interpret it as the fossilized content of the forestomach of the host whale and to identify the prey as belonging to the extant clupeiform genus Sardinops. Our discovery represents the first direct evidence of piscivory in an ancient edentulous mysticete. Since among modern mysticetes only Balaenopteridae are known to ordinarily consume fish, this fossil record may indicate that part of the cetotheriids experimented some degree of balaenopterid-like engulfment feeding. Moreover, this report corresponds to one of the geologically oldest records of Sardinops worldwide, occurring near the Tortonian peak of oceanic primary productivity and cooling phase. Therefore, our discovery evokes a link between the rise of Cetotheriidae; the setup of modern coastal upwelling systems; and the radiation of epipelagic, small-sized, schooling clupeiform fish in such highly productive environments.

  10. A multi-calibrated mitochondrial phylogeny of extant Bovidae (Artiodactyla, Ruminantia) and the importance of the fossil record to systematics

    PubMed Central

    2013-01-01

    Background Molecular phylogenetics has provided unprecedented resolution in the ruminant evolutionary tree. However, molecular age estimates using only one or a few (often misapplied) fossil calibration points have produced a diversity of conflicting ages for important evolutionary events within this clade. I here identify 16 fossil calibration points of relevance to the phylogeny of Bovidae and Ruminantia and use these, individually and together, to construct a dated molecular phylogeny through a reanalysis of the full mitochondrial genome of over 100 ruminant species. Results The new multi-calibrated tree provides ages that are younger overall than found in previous studies. Among these are young ages for the origin of crown Ruminantia (39.3–28.8 Ma), and crown Bovidae (17.3–15.1 Ma). These are argued to be reasonable hypotheses given that many basal fossils assigned to these taxa may in fact lie on the stem groups leading to the crown clades, thus inflating previous age estimates. Areas of conflict between molecular and fossil dates do persist, however, especially with regard to the base of the rapid Pecoran radiation and the sister relationship of Moschidae to Bovidae. Results of the single-calibrated analyses also show that a very wide range of molecular age estimates are obtainable using different calibration points, and that the choice of calibration point can influence the topology of the resulting tree. Compared to the single-calibrated trees, the multi-calibrated tree exhibits smaller variance in estimated ages and better reflects the fossil record. Conclusions The use of a large number of vetted fossil calibration points with soft bounds is promoted as a better approach than using just one or a few calibrations, or relying on internal-congruency metrics to discard good fossil data. This study also highlights the importance of considering morphological and ecological characteristics of clades when delimiting higher taxa. I also illustrate how

  11. Species-energy relationship in the deep sea: A test using the Quaternary fossil record

    USGS Publications Warehouse

    Hunt, G.; Cronin, T. M.; Roy, K.

    2005-01-01

    Little is known about the processes regulating species richness in deep-sea communities. Here we take advantage of natural experiments involving climate change to test whether predictions of the species-energy hypothesis hold in the deep sea. In addition, we test for the relationship between temperature and species richness predicted by a recent model based on biochemical kinetics of metabolism. Using the deep-sea fossil record of benthic foraminifera and statistical meta-analyses of temperature-richness and productivity-richness relationships in 10 deep-sea cores, we show that temperature but not productivity is a significant predictor of species richness over the past c. 130 000 years. Our results not only show that the temperature-richness relationship in the deep-sea is remarkably similar to that found in terrestrial and shallow marine habitats, but also that species richness tracks temperature change over geological time, at least on scales of c. 100 000 years. Thus, predicting biotic response to global climate change in the deep sea would require better understanding of how temperature regulates the occurrences and geographical ranges of species. ??2005 Blackwell Publishing Ltd/CNRS.

  12. Review of the monotreme fossil record and comparison of palaeontological and molecular data.

    PubMed

    Musser, A M

    2003-12-01

    Monotremes have traditionally been considered a remnant group of mammals descended from archaic Mesozoic stock, surviving to the present day on the relatively isolated Australian continent. Challenges to this orthodoxy have been spurred by discoveries of 'advanced' Cretaceous monotremes (Steropodon galmani, Archer, M., et al., 1985. First Mesozoic mammal from Australia-an Early Cretaceous monotreme, Nature. 318, 363-366) as well as by results from molecular data linking monotremes to therian mammals (specifically to marsupials in some studies). This paper reviews the monotreme fossil record and briefly discusses significant new information from additional Cretaceous Australian material. Mesozoic monotremes (including S. galmani) were a diverse group as evidenced by new material from the Early Cretaceous of New South Wales and Victoria currently under study. Although most of these new finds are edentulous jaws (limiting dental comparisons and determination of dietary niches), a range of sizes and forms has been determined. Some of these Cretaceous jaws exhibit archaic features-in particular evidence for the presence of a splenial bone in S. galmani-not seen in therian mammals or in post-Mesozoic (Tertiary and Quaternary) monotreme taxa. Tertiary monotremes were either archaic ornithorhynchids (toothed platypuses in the genera Monotrematum and Obdurodon) or tachyglossids (large echidnas in the genera Megalibgwilia and Zaglossus). Quaternary ornithorhynchid material is referable to the sole living platypus species Ornithorhynchus anatinus. Quaternary echidnas, however, were moderately diverse and several forms are known (Megalibgwilia species; 'Zaglossus' hacketti; Zaglossus species and Tachyglossus aculeatus). PMID:14667856

  13. On the development of probabilistic climate reconstructions based on fossil pollen records

    NASA Astrophysics Data System (ADS)

    Schoelzel, C.; Hense, A.

    2009-04-01

    Past climate reconstructions based on proxy data help to understand natural climate variability. It is essential that palaeoenvironmental transfer functions between climate and proxy variables take in to account the stochastical nature of the climate system. Especially pollen based reconstructions are a complex issue, since pollen counts do not show direct relation to climatological parameters, e.g. due to plant competition and/or land cultivation. The idea is to assess the background knowledge from classical, more empirically based methods in order to develop statistical transfer functions between vegetation and climate. Two popular concepts, the indicator taxa approach (or MCR) as well as the biomisation (BIOME/PFT), are translated into a statistical framework in order to reconstruct January and July temperatures as well as annual precipitation during the Holocene (10,000yrs BP). This involves the problem of multivariate random vectors with non-normally distributed marginals, which has been adressed by using copulas. The methods are applied to fossil pollen records of laminated sediments from the Eifel region in Germany. On the one hand, the reconstructions indicate that pollen based reconstructions show larger uncertainty ranges than expected by several classical approaches. On the other hand, the indicator taxa approach is robust to the lack of modern analogues, which is an advantage in highly anthropogenically influenced areas such as the Mediterranean or Central Europe.

  14. Anatomical Correlates to Nectar Feeding among the Strepsirrhines of Madagascar: Implications for Interpreting the Fossil Record

    PubMed Central

    Muchlinski, Magdalena N.; Perry, Jonathan M. G.

    2011-01-01

    One possible ecological scenario for the origin of primates is the archaic pollination and coevolution hypothesis. Its proponents contend that the consumption of nectar by some early primates and the resulting cross-pollination is an example of coevolution that drove adaptive radiations in some primates. This hypothesis is perhaps ecologically sound, but it lacks the morphology-behavior links that would allow us to test it using the fossil record. Here we attempt to identify cranial adaptations to nectar feeding among the strepsirrhines of Madagascar in order to provide such links. Many Malagasy strepsirrhines are considered effective cross-pollinators of the flowers they feed from, and nectar consumption represents as much as 75% of total feeding time. Previous studies identified skeletal correlates to nectar feeding in the crania of nonprimate mammals; from these, nine cranial measurements were chosen to be the focus of the present study. Results indicate that Cheirogaleus, Varecia, and Eulemur mirror other nectar-feeding mammals in having elongated crania and/or muzzles. These strepsirrhines might be effective cross-pollinators, lending support to the coevolution hypothesis. PMID:22567292

  15. Cell symbiosis [correction of symbioisis] theory: status and implications for the fossil record.

    PubMed

    Margulis, L; Stolz, J F

    1984-01-01

    Recent geological treatises have presented three alternative models of the origins of eukaryotes as if they merited equal treatment. However, modern biological techniques, especially nucleic acid and protein sequencing, have clearly established the validity of the symbiotic theory of the origin of eukaryotic organelles. The serial endosymbiotic theory in its most extreme form states that three classes of eukaryotic cell organelles (mitochondria, plastids and undulipodia) originated as free-living bacteria (aerobic respirers, phototrophic bacteria and spirochetes respectively) in association with hosts that become the nucleocytoplasm (Thermoplasma-like archaebacterial hosts). Molecular biological information, primarily derived from ribosomal RNA nucleotide sequencing studies leads to the conclusion that the symbiotic origin theory for both mitochondria and plastids has been proven. The probability of an ancestral archaebacterial-Thermoplasma-like host for the nucleocytoplasm has been rendered more likely by discoveries by Dennis Searcy and his colleagues and Carl Woese and his colleagues. The most equivocal postulate of the symbiotic theory, the origin of undulipodia (cilia and other organelles of motility that develop from kinetosomes is under investigation now. The status of these postulates, as well as their implications for the fossil record, is briefly summarized here. PMID:11537775

  16. Dietary correlates associated with the mental foramen in primates: implications for interpreting the fossil record.

    PubMed

    Muchlinski, Magdalena N; Deane, Andrew S

    2016-07-01

    The mandibular nerve is a sensory and motor nerve that innervates the muscles of mastication, the lower dentition, and the lower lip and surrounding structures. Although this nerve contains both efferent and afferent fibers, the mental nerve, a terminal branch of the mandibular nerve, is a strictly sensory nerve that exits the mental foramen and innervates the lower lip, the skin overlaying the mandible, and the oral mucosa around the mandible. Osteological foramina are often used as proxies for nerve cross section area and they often correlate well with some aspect of a primate's ecology (e.g., optic foramen and visual acuity). The primary objective of this study is to explore the correlation between the mental foramen and dietary preference among primates. The mental foramen of 40 primate species (n = 180) was measured from 3-D surface models of the mandible. Both conventional and phylogenetic tests indicate that although frugivores have larger mental foramina than folivores, the differences were not significant. These results show that while structures like the infraorbital foramen correlate well with diet and touch sensitivity, the mental foramen does not. Based on these findings, the mental foramen is not a suggested morphological character for interpreting of the fossil record. J. Morphol. 277:978-985, 2016. © 2016 Wiley Periodicals, Inc. PMID:27130849

  17. First forensic records of termite activity on non-fossilized human bones in Brazil.

    PubMed

    Queiroz, R A; Soriano, E P; Carvalho, M V D; Caldas-Junior, A F; Souza, E H A; Coelho-Junior, L G T M; Campello, R I C; Almeida, A C; Farias, R C A P; Vasconcellos, A

    2016-07-25

    The aim of this study was to describe the first records of termite activity on non-fossilized human bones in Brazil. The cases reported in this study resulted from forensic analysis of six human skeletons found in northeastern Brazil between 2012 and 2014. Traces of tunnels and nests commonly produced by termites were found on several human bone surfaces as well as the specimens and characteristic signs of osteophagic activity. In four cases, the species were identified: Amitermes amifer Silvestri, 1901, Nasutitermes corniger (Motschulsky, 1855) (on two skeletons), and Microcerotermes indistinctus Mathews, 1977. In two other cases, the activity of termites on bone surfaces was evidenced by remains of nests and tunnels produced by these insects. At least in the samples of human remains available for this report, the number of termites collected was greater on bones found during autumn, the rainy season in the Northeast of Brazil. The human bones examined showed termites like insects with lots of strength at bone degradation, capable of continuing the process of decomposition of human remains even in completely skeletonized bodies. PMID:27463832

  18. Fossil bryophytes as recorders of ancient CO2 levels: Experimental evidence and a Cretaceous case study

    NASA Astrophysics Data System (ADS)

    Fletcher, Benjamin J.; Beerling, David J.; Brentnall, Stuart J.; Royer, Dana L.

    2005-09-01

    Biological and geochemical CO2 proxies provide critical constraints on understanding the role of atmospheric CO2 in driving climate change during Earth history. As no single existing CO2 proxy is without its limitations, there is a clear need for new approaches to reconstructing past CO2 concentrations. Here we develop a new pre-Quaternary CO2 proxy based on the stable carbon isotope composition (δ13C) of astomatous land plants. In a series of CO2-controlled laboratory experiments, we show that the carbon isotope discrimination (Δ13C) of a range of bryophyte (liverwort and moss) species increases with atmospheric CO2 across the range 375 to 6000 ppm. Separate experiments establish that variations in growth temperature, water content and substrate type have minor impacts on the Δ13C of liverworts but not mosses, indicating the greater potential of liverworts to faithfully record past variations in CO2. A mechanistic model for calculating past CO2 concentrations from bryophyte Δ13C (White et al., 1994) is extended and calibrated using our experimental results. The potential for fossil liverworts to record past CO2 changes is investigated by analyzing the δ13C of specimens collected from Alexander Island, Antarctica dating to the "greenhouse" world of the mid-Cretaceous. Our analysis and isotopic model yield mid-Cretaceous CO2 concentrations of 1000-1400 ppm, in general agreement with independent proxy data and long-term carbon cycle models. The exceptionally long evolutionary history of bryophytes offers the possibility of reconstructing CO2 concentrations back to the mid-Ordovician, pre-dating all currently used quantitative CO2 proxies.

  19. A High-Resolution Record of Early Miocene Antarctic Glacial History From Downhole Logs, Site 1165, ODP Leg 188

    NASA Astrophysics Data System (ADS)

    Williams, T.; Barr, S.; Handwerger, D.

    2002-12-01

    ODP Site 1165, located 400 km NW of Prydz Bay, contains the most detailed record yet obtained of Early Miocene Antarctic glacial history. The 520-m-thick Early Miocene consists of dark grey claystone with silt laminae (contourites) alternating with decimeter-scale layers of greenish-grey bioturbated claystone that contain common ice rafted debris (IRD). These sediments are interpreted to record pulses of IRD from the continent, and alternations in the position or strength of the currents at the site. Downhole logs of electrical resistivity, natural gamma radiation, and density also record the alternations between the two facies. Here we assess the lithological significance of the logs by examining the opal, IRD, and susceptibility of two short intervals at high resolution, with samples taken every 10 cm, or about 1250 yr. The IRD-bearing greenish-grey claystone corresponds to higher resistivity and density because of increased cementation by silica, and corresponds to lower natural gamma radiation because of decreased clay content. Thus, using the logs, lithology can be inferred for intervals where no core was recovered. Based mainly on magnetostratigraphy, the age of the base of the hole is 22 Ma, and the sedimentation rate for the Early Miocene about 9 cm/kyr. The regular spacing of the facies alternations in the logs suggests they are astronomically paced. Between 18-20 Ma, the main periodicity is in the precessional range, and between 20-22 Ma, the logs have a saw-toothed form, with a major peak in IRD at the beginning of each, repeating about every 100 kyr. We think that the IRD pulses represent deglaciations. Hence our data suggest that the Antarctic continent, at least around the Prydz Bay region, was glaciated in the Early Miocene, and that the size of the ice sheet oscillated on Milankovitch time scales.

  20. Ancestral state reconstruction of body size in the Caniformia (Carnivora, Mammalia): the effects of incorporating data from the fossil record.

    PubMed

    Finarelli, John A; Flynn, John J

    2006-04-01

    A recent molecular phylogeny of the mammalian order Carnivora implied large body size as the ancestral condition for the caniform subclade Arctoidea using the distribution of species mean body sizes among living taxa. "Extant taxa-only" approaches such as these discount character state observations for fossil members of living clades and completely ignore data from extinct lineages. To more rigorously reconstruct body sizes of ancestral forms within the Caniformia, body size and first appearance data were collected for 149 extant and 367 extinct taxa. Body sizes were reconstructed for four ancestral nodes using weighted squared-change parsimony on log-transformed body mass data. Reconstructions based on extant taxa alone favored large body sizes (on the order of 10 to 50 kg) for the last common ancestors of both the Caniformia and Arctoidea. In contrast, reconstructions incorporating fossil data support small body sizes (< 5 kg) for the ancestors of those clades. When the temporal information associated with fossil data was discarded, body size reconstructions became ambiguous, demonstrating that incorporating both character state and temporal information from fossil taxa unambiguously supports a small ancestral body size, thereby falsifying hypotheses derived from extant taxa alone. Body size reconstructions for Caniformia, Arctoidea, and Musteloidea were not sensitive to potential errors introduced by uncertainty in the position of extinct lineages relative to the molecular topology, or to missing body size data for extinct members of an entire major clade (the aquatic Pinnipedia). Incorporating character state observations and temporal information from the fossil record into hypothesis testing has a significant impact on the ability to reconstruct ancestral characters and constrains the range of potential hypotheses of character evolution. Fossil data here provide the evidence to reliably document trends of both increasing and decreasing body size in several

  1. Recording of climate and diagenesis through fossil pigments and sedimentary DNA at Laguna Potrok Aike, Argentina

    NASA Astrophysics Data System (ADS)

    Vuillemin, A.; Ariztegui, D.; Leavitt, P. R.; Bunting, L.; Pasado Science Team

    2015-11-01

    Aquatic sediments record past climatic conditions while providing a wide range of ecological niches for microorganisms. Although marine sedimentary microbial assemblages are often defined by their surrounding geochemical conditions, the influence of environmental features upon microbial development and post-depositional survival remains largely unknown in the lacustrine realm. Due to long-term microbial activity, the composition of environmental DNA can be expected to evolve with sediment depth and over time and therefore should reflect both ancient and extant microbial populations, but this hypothesis has rarely been tested using a multiproxy approach. Here geomicrobiological and phylogenetic analyses of a Patagonian maar lake were used to indicate that the different sedimentary microbial assemblages derive from specific lacustrine regimes during defined climatic periods. Two well defined climatic intervals whose sediments harboured active microbial populations and measurable ATP were sampled for a comparative environmental study based on fossil pigments and 16S rRNA gene sequences. Bacterial and archaeal 16S rRNA gene sequences recovered from the Holocene record revealed a microbial community adapted to subsaline conditions actively producing methane during organic matter degradation. These characteristics were associated with sediments resulting from endorheic lake conditions with high evaporative stress and concomitant high algal productivity. Moreover, archaeal clone libraries established throughout the Holocene record indicate an age-related stratification of these populations, consistent with a gradual use of organic substrates after deposition. In contrast, sulphate-reducing bacteria and lithotrophic Archaea were predominant in sediments dated from the Last Glacial Maximum, in which pelagic clays alternated with fine volcanic material characteristic of a lake level highstand and freshwater conditions, but reduced water column productivity. These patterns

  2. Antarctic ecosystems as models for extraterrestrial surface habitats

    NASA Astrophysics Data System (ADS)

    Wynn-Williams, D. D.; Edwards, H. G. M.

    2000-09-01

    Surface habitats in Antarctic deserts are near the limits of life on Earth and resemble those hypothesized for early Mars. Cyanobacteria dominate the transient riverbeds, stromatolitic sediments in ice-covered lakes, and endolithic communities in translucent rock. There is still no direct evidence of photosynthetic life on early Mars, but cyanobacteria are amongst the earliest microbes detectable in the fossil record for analogous habitats on Earth. Key biomolecules persist in Antarctic microbial habitats, even after extinction by excessive low temperatures, desiccation and UV-B stress within the Ozone Hole. Pigments (or their fossil residues), such as chlorophyll and the UV-protectants scytonemin, carotene and quinones, are good biomarkers. To show not only their presence but also their micro-spatial distribution in situ, we describe the use of FT-Raman spectroscopy with 1064 nm excitation to avoid autofluorescence from the pigments. We report not only the diversity of biomolecules that we have diagnosed from their unique Raman spectra of Antarctic cyanobacterial communities, but also their functional stratification in endolithic communities. Our analyses of Antarctic habitats show the potential of this remote, non-intrusive technique to probe for buried biomolecules on future Mars missions and in Antarctic Lake Vostok, >4 km beneath the Central Ice Sheet, with implications for the putative analogous sub-ice ocean on Europa.

  3. Historical whaling records reveal major regional retreat of Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Cotté, Cédric; Guinet, Christophe

    2007-02-01

    Several studies have provided evidence of a reduction of the Antarctic sea ice extent. However, these studies were conducted either at a global scale or at a regional scale, and possible inter-regional differences were not analysed. Using the long-term whaling database we investigated circum-Antarctic changes in summer sea ice extent from 1931 to 1987. Accounting for bias inherent in the whaling method, this analysis provides new insight into the historical ice edge reconstruction and inter-regional differences. We highlight a reduction of the sea ice extent occurring in the 1960s, mainly in the Weddell sector where the change ranged from 3° to 7.9° latitude through summer. Although the whaling method may not be appropriate for detecting fine-scale change, these results provide evidence for a heterogeneous circumpolar change of the sea ice extent. The shift is temporally and spatially consistent with other environmental changes detected in the Weddell sector and also with a shift in the Southern Hemisphere annular mode. The large reduction of the sea ice extent has probably influenced the ecosystem of the Weddell Sea, particularly the krill biomass.

  4. Decay of vertebrate characters in hagfish and lamprey (Cyclostomata) and the implications for the vertebrate fossil record

    PubMed Central

    Sansom, Robert S.; Gabbott, Sarah E.; Purnell, Mark A.

    2011-01-01

    The timing and sequence of events underlying the origin and early evolution of vertebrates remains poorly understood. The palaeontological evidence should shed light on these issues, but difficulties in interpretation of the non-biomineralized fossil record make this problematic. Here we present an experimental analysis of decay of vertebrate characters based on the extant jawless vertebrates (Lampetra and Myxine). This provides a framework for the interpretation of the anatomy of soft-bodied fossil vertebrates and putative cyclostomes, and a context for reading the fossil record of non-biomineralized vertebrate characters. Decay results in transformation and non-random loss of characters. In both lamprey and hagfish, different types of cartilage decay at different rates, resulting in taphonomic bias towards loss of ‘soft’ cartilages containing vertebrate-specific Col2α1 extracellular matrix proteins; phylogenetically informative soft-tissue characters decay before more plesiomorphic characters. As such, synapomorphic decay bias, previously recognized in early chordates, is more pervasive, and needs to be taken into account when interpreting the anatomy of any non-biomineralized fossil vertebrate, such as Haikouichthys, Mayomyzon and Hardistiella. PMID:20947532

  5. Evolutionary innovations in the fossil record: the intersection of ecology, development, and macroevolution.

    PubMed

    Jablonski, David

    2005-11-15

    The origins of evolutionary innovations have been intensively studied, but relatively little is known about their large-scale ecological patterns. For post-Paleozoic benthic marine invertebrates, which have the richest and most densely sampled fossil record, order-level taxa tend to appear first in onshore, disturbed habitats, even in groups that are now exclusively deep-water (so that present-day distributions are not reliable indicators of original environments). New results presented here show that the onshore-origination pattern is robust to shifts in taxonomic methods and to new paleontological discoveries, and the few available studies suggest that this pattern can also be seen in terms of excursions in morphospace or the acquisition of derived character states, without reference to taxonomic categories. The environmental pattern at high levels contrasts significantly with the origin of low-level novelties (such as defined genera and families) in crinoids, echinoids, and bryozoans, where first appearances tend to conform to their clade-specific bathymetric diversity gradients. This discordance seems to eliminate potential driving mechanisms that simply scale up within-population genetic or ecological processes. Little is known about the factors that promote the onshore-offshore expansion of orders across the continental shelf, or that drive some clades to abandon ancestral habitats for an exclusively deep-water distribution. The origin of evolutionary innovation must ultimately reside in developmental changes, but the onshore-origination bias could emerge from two different dynamics: the pattern could be primarily genetic and developmental, i.e., innovations truly arise onshore; or primarily ecological, i.e., innovations arise randomly but preferentially survive onshore. Whatever the ultimate driving mechanisms, these macroevolutionary patterns show that theories of large-scale evolutionary novelty must include an ecological dimension. PMID:16161067

  6. Egg size evolution in tropical American arcid bivalves: the comparative method and the fossil record.

    PubMed

    Moran, Amy L

    2004-12-01

    Marine organisms exhibit a wide range of egg sizes, even among closely related taxa, and egg size is widely considered to be one of the most important components of the life histories of marine species. The nature of the trade-off between egg size and number and the consequences of variation in egg size for offspring growth and survivorship have been extensively modeled. Yet, there is little empirical evidence that supports the relative importance of particular environmental parameters in engendering the tremendous variation in egg size seen in marine organisms. This study compares egg sizes between six geminate species pairs of bivalves in the family Arcidae to determine whether egg size differs in predictable directions between geminate species in the two oceans separated by the Central American isthmus, and whether the direction and timing of egg size evolution among geminates in this family is correlated with both modern and paleoceanographic patterns of oceanic productivity. In all modern members of six geminate pairs, egg size was larger in the species in the western Atlantic than in its sister species the eastern Pacific. This pattern supports the hypothesis that optimal egg size differs in the two oceans due to the low productivity and poor larval feeding environment in the western Atlantic relative to the eastern Pacific. The fossil record of one geminate pair shows that egg size has remained consistently large in the western Atlantic from the Miocene to the Recent, while egg size in the eastern Pacific has decreased to the current small size in less than 2 million years; this suggests that modern-day differences between egg sizes in the western Atlantic and eastern Pacific are due to either an increase in productivity in the eastern Pacific and subsequent selection for smaller eggs in that ocean, or differential patterns of extinction that occurred well after the rise of the isthmus. These results agree with ancestral character state reconstruction using

  7. A new Eemian record of Antarctic tephra layers retrieved from the Talos Dome ice core (Northern Victoria Land)

    NASA Astrophysics Data System (ADS)

    Narcisi, Biancamaria; Petit, Jean Robert; Langone, Antonio; Stenni, Barbara

    2016-02-01

    Polar ice sheets are remarkable repositories of tephra layers. The Talos Dome ice core (72°49‧S, 159°11‧E), drilled at the edge of the East Antarctic Plateau, close to Late Quaternary volcanoes, offers considerable potential to extend the current tephra time-stratigraphic framework. A tephrochronological study was undertaken of the ice core sections related to the Last Interglacial and the transition to the subsequent glacial period. Thirteen macroscopically visible layers, interpreted to be related to primary deposition of fallout tephra, have been analysed for quantitative grain size and glass shard geochemistry. The layers, precisely framed within the climate (δ18O) record for the core, span in age from 111.6 ± 1.9 to 123.3 ± 2.2 ka. Coarse particle size suggests origin from regional sources. Indeed, the vast majority of the samples display an alkaline affinity and trachytic composition that are both typical geochemical features of rifting Antarctic volcanism. Using subtle differences in the geochemical signatures and the comparison with data from previous studies, a few layers are attributed to known coeval Mt. Melbourne eruptions. Another sample subset is consistent with derivation from The Pleiades and Mt. Rittmann volcanoes. One peculiar trachytic glass population appears to be related to activity of the more distant Marie Byrd Land volcanoes. The newly detected tephras provide stratigraphic markers that could facilitate future synchronisation and dating of palaeoclimatic records. The Talos Dome tephra inventory also contributes significantly to the reconstruction of the Northern Victoria Land explosive volcanism, for which chronostratigraphic data for the Last Interglacial temporal segment are poor.

  8. Palaeontology: The Point of No Return in the Fossil Record of Eusociality.

    PubMed

    Rust, Jes; Wappler, Torsten

    2016-02-22

    The evolution of eusociality is one of the major transitions in the history of life, particularly in the insects. Now, fossil termites and ants from Burmese amber offer insights into early stages of eusociality in the Lower Cretaceous. PMID:26906485

  9. A long-term association between global temperature and biodiversity, origination and extinction in the fossil record

    PubMed Central

    Mayhew, Peter J; Jenkins, Gareth B; Benton, Timothy G

    2007-01-01

    The past relationship between global temperature and levels of biological diversity is of increasing concern due to anthropogenic climate warming. However, no consistent link between these variables has yet been demonstrated. We analysed the fossil record for the last 520 Myr against estimates of low latitude sea surface temperature for the same period. We found that global biodiversity (the richness of families and genera) is related to temperature and has been relatively low during warm ‘greenhouse’ phases, while during the same phases extinction and origination rates of taxonomic lineages have been relatively high. These findings are consistent for terrestrial and marine environments and are robust to a number of alternative assumptions and potential biases. Our results provide the first clear evidence that global climate may explain substantial variation in the fossil record in a simple and consistent manner. Our findings may have implications for extinction and biodiversity change under future climate warming. PMID:17956842

  10. Piscivory in a Miocene Cetotheriidae of Peru: first record of fossilized stomach content for an extinct baleen-bearing whale.

    PubMed

    Collareta, Alberto; Landini, Walter; Lambert, Olivier; Post, Klaas; Tinelli, Chiara; Di Celma, Claudio; Panetta, Daniele; Tripodi, Maria; Salvadori, Piero A; Caramella, Davide; Marchi, Damiano; Urbina, Mario; Bianucci, Giovanni

    2015-12-01

    Instead of teeth, modern mysticetes bear hair-fringed keratinous baleen plates that permit various bulk-filtering predation techniques (from subsurface skimming to lateral benthic suction and engulfment) devoted to various target prey (from small invertebrates to schooling fish). Current knowledge about the feeding ecology of extant cetaceans is revealed by stomach content analyses and observations of behavior. Unfortunately, no fossil stomach contents of ancient mysticetes have been described so far; the investigation of the diet of fossil baleen whales, including the Neogene family Cetotheriidae, remains thus largely speculative. We report on an aggregate of fossil fish remains found within a mysticete skeleton belonging to an undescribed late Miocene (Tortonian) cetotheriid from the Pisco Formation (Peru). Micro-computed tomography allowed us to interpret it as the fossilized content of the forestomach of the host whale and to identify the prey as belonging to the extant clupeiform genus Sardinops. Our discovery represents the first direct evidence of piscivory in an ancient edentulous mysticete. Since among modern mysticetes only Balaenopteridae are known to ordinarily consume fish, this fossil record may indicate that part of the cetotheriids experimented some degree of balaenopterid-like engulfment feeding. Moreover, this report corresponds to one of the geologically oldest records of Sardinops worldwide, occurring near the Tortonian peak of oceanic primary productivity and cooling phase. Therefore, our discovery evokes a link between the rise of Cetotheriidae; the setup of modern coastal upwelling systems; and the radiation of epipelagic, small-sized, schooling clupeiform fish in such highly productive environments. PMID:26553062

  11. Fossil Crinoids

    NASA Astrophysics Data System (ADS)

    Hess, Hans; Ausich, William I.; Brett, Carlton E.; Simms, Michael J.

    2003-01-01

    Crinoids have graced the oceans for more than 500 million years. Among the most attractive fossils, crinoids had a key role in the ecology of marine communities through much of the fossil record, and their remains are prominent rock forming constituents of many limestones. This is the first comprehensive volume to bring together their form and function, classification, evolutionary history, occurrence, preservation and ecology. The main part of the book is devoted to assemblages of intact fossil crinoids, which are described in their geological setting in twenty-three chapters ranging from the Ordovician to the Tertiary. The final chapter deals with living sea lilies and feather stars. The volume is exquisitely illustrated with abundant photographs and line drawings of crinoids from sites around the world. This authoritative account recreates a fascinating picture of fossil crinoids for paleontologists, geologists, evolutionary and marine biologists, ecologists and amateur fossil collectors.

  12. Fossil Crinoids

    NASA Astrophysics Data System (ADS)

    Hess, Hans; Ausich, William I.; Brett, Carlton E.; Simms, Michael J.

    1999-10-01

    Crinoids have graced the oceans for more than 500 million years. Among the most attractive fossils, crinoids had a key role in the ecology of marine communities through much of the fossil record, and their remains are prominent rock forming constituents of many limestones. This is the first comprehensive volume to bring together their form and function, classification, evolutionary history, occurrence, preservation and ecology. The main part of the book is devoted to assemblages of intact fossil crinoids, which are described in their geological setting in twenty-three chapters ranging from the Ordovician to the Tertiary. The final chapter deals with living sea lilies and feather stars. The volume is exquisitely illustrated with abundant photographs and line drawings of crinoids from sites around the world. This authoritative account recreates a fascinating picture of fossil crinoids for paleontologists, geologists, evolutionary and marine biologists, ecologists and amateur fossil collectors.

  13. A Bivalve Proxy for Neogene Antarctic Shelf Marine Environments

    NASA Astrophysics Data System (ADS)

    Clark, N. A.; Williams, M.; Quilty, P. G.; Leng, M. J.; Zalasiewicz, J. A.; Smellie, J.; Dowsett, H. J.

    2012-12-01

    The Neogene shallow-marine successions of the Antarctic Peninsula and of the East Antarctic region preserve rich assemblages of bivalve molluscs. These bivalve molluscs provide a detailed record of palaeoseasonality in the chemical signature and morphology of their shells that can be used to assess sea temperatures and sea ice extent for the Antarctic shelf during the Pliocene. Analyses identify the following. 1) Neogene bivalves from James Ross Island, Antarctic Peninsula, comprise material of late Miocene through to late Pliocene age. Results identify warm (ca. 3-10 °C) early Pliocene sea temperatures, and cooler late Pliocene sea temperatures (ca. 0-4 °C), and flag a cooling trend which is consistent with the evolution of polar climate through this interval. 2) Neogene bivalves from the Larsemann Hills, East Antarctic, identify generally warmer than present sea temperatures (ca. 0-11 °C) in the early Pliocene consistent with data from other fossil groups of this age, including dolphins and silicoflagellates. The new data may provide significant ground truth for climate models assessing the Southern Ocean and Antarctic shelf climate.

  14. Expanding Ice Sheets on the Antarctic Peninsula during the Plio/Pleistocene Recorded in Continental Rise Sediment Drifts

    NASA Astrophysics Data System (ADS)

    Cowan, E. A.; Hillenbrand, C.

    2007-12-01

    Sediment drifts on the continental rise west of the Antarctic Peninsula are located within 125 km from the continental shelf edge, the main contributor of terrigenous sediment during both glacial and interglacial periods. The composition of drift deposits continuously recorded changes in ice sheet volume and thermal regime as well as sea surface temperatures (SSTs) and sea ice extent. The coarse-grained terrigenous sediment (pebbles and coarse sand), a proxy for iceberg-rafted debris (IRD), was analyzed in sediments spanning the last 3.1 m.y. at Ocean Drilling Program (ODP) Sites 1101 and 1096. IRD is deposited in both glacial intervals, dominated by fine-grained laminated mud and interglacial units consisting of bioturbated muds enriched in biogenic components. Contents of biogenic opal, which reflect diatom abundance, are relatively high from 3.1-2.2 Ma. Calcareous nannofossils are present within interglacial sediments from 2.2-0.76 Ma. Both findings suggest warm SSTs and limited sea ice over the drifts during interglacial periods before the Late Pleistocene. Quartz grains picked from the IRD fraction and imaged with a scanning electron microscope (SEM) show an abrupt change in surface microtextures at 1.35 Ma. During the Late Pliocene to Early Pleistocene, many quartz grains are completely weathered and only a few show signs of crushing and abrasion, indicating that glaciers were too small to inundate the Antarctic Peninsula topography. Debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass unmodified through the glaciers. Glaciers expanded in size during glacial periods from 1.35-0.76 Ma. The IRD accumulation during those periods was very high and diverse dropstone lithologies document supply from sources throughout the Antarctica Peninsula. Conditions that spawned the large polar ice sheet identified at the Last Glacial Maximum have been present on the Antarctic Peninsula during glacial periods since

  15. First geomorphological record and glacial history of an inter-ice stream ridge on the West Antarctic continental shelf

    NASA Astrophysics Data System (ADS)

    Klages, J. P.; Kuhn, G.; Hillenbrand, C.-D.; Graham, A. G. C.; Smith, J. A.; Larter, R. D.; Gohl, K.

    2013-02-01

    Inter-ice stream areas cover significant portions of Antarctica's formerly glaciated shelves, but have been largely neglected in past geological studies because of overprinting by iceberg scours. Here, we present results of the first detailed survey of an inter-ice stream ridge from the West Antarctic continental shelf. Well-preserved sub- and proglacial bedforms on the seafloor of the ridge in the eastern Amundsen Sea Embayment (ASE) provide new insights into the flow dynamics of this sector of the West Antarctic Ice Sheet (WAIS) during the Last Glacial cycle. Multibeam swath bathymetry and PARASOUND acoustic sub-bottom profiler data acquired across a mid-shelf bank, between the troughs of the Pine Island-Thwaites (PITPIS) and Cosgrove palaeo-ice streams (COPIS), reveal large-scale ribbed moraines, hill-hole pairs, terminal moraines, and crevasse-squeeze ridges. Together, these features form an assemblage of landforms that is entirely different from that in the adjacent ice-stream troughs, and appears to be unique in the context of previous studies of Antarctic seafloor geomorphology. From this assemblage, the history of ice flow and retreat from the inter-ice stream ridge is reconstructed. The bedforms indicate that ice flow was significantly slower on the inter-ice stream ridge than in the neighbouring troughs. While terminal moraines record at least two re-advances or stillstands of the ice sheet during deglaciation, an extensive field of crevasse-squeeze ridges indicates ice stagnation subsequent to re-advancing ice, which deposited the field of terminal moraines in the NE. The presented data suggest that the ice flow behaviour on the inter-ice stream ridge was substantially different from that in the adjacent troughs. However, newly obtained radiocarbon ages on two sediment cores recovered from the inter-ice stream ridge suggest a similar timing in the deglaciation of both areas. This information closes an important gap in the understanding of past WAIS

  16. Solar vs. Tidal Forcing of Centennial to Decadal Scale Variability in Marine Sedimentary Records from the Western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Kirkwood, G.; Domack, E.; Brachfeld, S.

    2004-12-01

    Prior studies on Holocene marine sediments from the Antarctic Peninsula, including ODP Site 1098 and USAP N. B. Palmer jumbo piston cores have revealed pronounced multi-century scale variations within a number of paleoenvironmental proxies. In order to fully understand the exact timing of this signal an ultra-high resolution jumbo piston core from the Schollaert Drift was correlated with the well-known Palmer Deep record. A precise and accurate radiocarbon chronology is now available from the former site that utilizes in-situ mollusks, rather than bulk organic matter. The resulting time series spans the last 5000 years over the 20 m length of core NBP99-03 JPC28 and the surface stratigraphy of kasten core NBP01-07 KC8. The corrected and calibrated ages (with an applied reservoir correction of 1170 years) of 10 mollusks dated by the National Ocean Sciences Accelerator Mass Spectrometry Facility and the University of Arizona TAMS facility were used to construct an age-depth profile for JPC28 and KC8. A linear trend (R2 value of 0.993) of the age-depth profile was used to extrapolate the constant time interval between magnetic susceptibility measurements, which were analyzed every 1 cm. Dominant periods in the upper 10 m of the time series were identified using the Arand Spectral Analysis Package (Howell, 2001). This analysis revealed a single pronounced maxima at 160 years, which is inconsistent with the dominant periods found in time series of climate proxies from other sites on the western side of the Antarctic Peninsula. In particular, periods of 200 and 400 years, which are dominant in the Palmer Deep site (Warner and Domack, 2002), are not present in the Schollaert Drift. The spectral peaks derived from the two records are significantly different at the 95% confidence level. The cycles in the Palmer Deep record have been associated with solar variability, where as the 160 year cycle in the Schollaert Drift is close to a 180 year cycle in tidal forces (Keeling

  17. Ghost shrimp Calliax de Saint Laurent, 1973 (Decapoda: Axiidea: Callianassidae) in the fossil record: systematics, palaeoecology and palaeobiogeography

    PubMed Central

    HYŽNÝ, MATÚŠ; GAŠPARIČ, ROK

    2015-01-01

    Ghost shrimps of the family Callianassidae are very common in the fossil record, but mostly as isolated cheliped elements only. The assignment to biologically defined genera, diagnosed on the basis of soft part morphology, is thus rather difficult. In this respect, proxy characters present on chelipeds that are the most durable ghost shrimp remains are needed to ascribe fossil material to extant genera. The genus Calliax de Saint Laurent, 1973 has been particularly obscure in this respect. Thorough comparison of extant members of the genus resulted in evaluation of characters present on chelipeds being taxonomically important on the genus level, specifically: 1) rectangular major P1 propodus with two ridges on the base of the fixed finger extending onto manus; 2) major P1 fingers relatively short; and 3) minor P1 chela with dactylus longer than fixed finger and possessing a wide gap between fingers. On this basis, Callianassa michelottii A. Milne Edwards, 1860, from the Oligocene and Miocene of Europe is herein reassigned to Calliax. Further re-examination of the ghost shrimp fossil record revealed that C. szobensis Müller, 1984, from the Middle Miocene of Hungary represents the same animal as C. michelottii and they are synomymised herein. The known geographic distribution of C. michelottii is expanded by the first confirmed occurrence of the species in Slovakia. All occurrences of C. michelottii known to date are reviewed and documented. The presence of Calliax michelottii comb. nov. may be considered an indicator of deeper marine settings. Based on the scarce fossil record known to date, Calliax has a Tethyan origin; it supposedly migrated westward to establish present day communities in the Caribbean sometime before the Middle Miocene. PMID:24989725

  18. Molecular and isotopic composition of lipids in modern and fossil bivalve shells: Records of paleoenvironmental change?

    SciTech Connect

    CoBabe, E.A.

    1995-12-31

    Suites of lipids residing in situ in modern and fossil bivalve shells offer new possibilities for the study of paleoecology and paleoclimatology. Distributions of carbon isotopic compositions of modem shell lipids suggests that many of these compounds, including alkanes, sterols, fatty acids, ketones and phytadienes, are derived from the bivalves and not directly from the surrounding environment. The occurrence of fatty acids in modem and fossil shell material opens up the possibility that saturation levels of these compounds may be used as paleothermometers. To date, the utility of fatty acids in paleoclimate studies has been limited because of the swift breakdown of these compounds in sediment. However, initial results indicate that fatty acids in bivalve shells retain their original structure for at least several million years. Comparison of modem bivalve shell fatty acids from tropical, temperate and polar nearshore marine systems will be presented, along with analogous fossil data.

  19. Two Years of Plankton Tows in a Seasonal Upwelling Region: Foraminiferal Abundances and Implications for the Fossil Record

    NASA Astrophysics Data System (ADS)

    Davis, C. V.; Hill, T. M.; Jahncke, J.

    2014-12-01

    Planktic foraminifera have a long history of use as paleoceaographic proxies due to their environmental sensitivity, cosmopolitan distribution and extensive fossil record. The seasonal, spatial and water mass affinities of foraminifera species have implications for the interpretation of fossil assemblages and the interpretation of shell geochemistry. Two years (2012-2014) of shallow (<200 m) plankton tows, taken along the continental shelf inside the California Current system, offer new insights into the spatial and seasonal dynamics of planktic foraminifera in an upwelling regime. Tows along with intensive hydrologic monitoring by CTD casts and discrete bottle sampling (temperature, salinity, oxygen, thermocline depth, carbonate saturation state) have spanned two complete seasonal upwelling-relaxation cycles. We present the results from these tows as well as preliminary models linking environmental drivers and foraminifera assemblages in this highly dynamic environment. Species abundances appear to be highly seasonal, in keeping with water column structure, with a seasonal upwelling to relaxation trade off between the non-spinose foraminifers Neogloboquadrina pachyderma and Neogloboquadrina incompta. We focus on the implications of species seasonality and hydrologic affinities to the interpretation of the fossil record in upwelling regions.

  20. A first record of Cretaceous aphids (Hemiptera, Sternorrhyncha, Aphidomorpha) in Australia, from the Lower Cretaceous Koonwarra Fossil Bed, Victoria.

    PubMed

    Martin, Sarah K; Skidmore, Luke I; Stilwell, Jeffrey D

    2016-01-01

    This paper describes the first species of aphid from the Lower Cretaceous Koonwarra Fossil Bed of the Gippsland Basin, southeastern Victoria, Australia. This aphid, herein named Koonwarraphis rotundafrons gen. & sp. nov., is assigned to the cosmopolitan Cretaceous superfamily Tajmyraphidoidea, which has been previously described from the Lebanese, Taimyrian, Canadian, Myanmar (Burmese), and Spanish ambers. Koonwarraphis rotundafrons is the first aphid recorded from the eastern Gondwanan landmass during the Cretaceous, and represents the only tajmyraphidoid preserved as a compression fossil, rather than as an amber inclusion. Due to the nature of the fossil's preservation, Koonwarraphis cannot be firmly placed in any of the described tajmyraphidoid families; however, all observable morphological features suggest that the genus is broadly typical of the superfamily and Cretaceous aphids in general. Koonwarraphis' shortened rostrum, a feature also seen in other tajmyraphidoids, suggests an association with the more herbaceous aspects of the Early Cretaceous Victorian flora. Considering the modern aphid preference for angiosperm plants, it is possible that this aphid was living upon the herbaceous early angiosperms recorded previously from the Koonwarra macrofloral assemblage. PMID:27395744

  1. The First Occurrence in the Fossil Record of an Aquatic Avian Twig-Nest with Phoenicopteriformes Eggs: Evolutionary Implications

    PubMed Central

    Grellet-Tinner, Gerald; Murelaga, Xabier; Larrasoaña, Juan C.; Silveira, Luis F.; Olivares, Maitane; Ortega, Luis A.; Trimby, Patrick W.; Pascual, Ana

    2012-01-01

    Background We describe the first occurrence in the fossil record of an aquatic avian twig-nest with five eggs in situ (Early Miocene Tudela Formation, Ebro Basin, Spain). Extensive outcrops of this formation reveal autochthonous avian osteological and oological fossils that represent a single taxon identified as a basal phoenicopterid. Although the eggshell structure is definitively phoenicopterid, the characteristics of both the nest and the eggs are similar to those of modern grebes. These observations allow us to address the origin of the disparities between the sister taxa Podicipedidae and Phoenicopteridae crown clades, and traces the evolution of the nesting and reproductive environments for phoenicopteriforms. Methodology/Principal Findings Multi-disciplinary analyses performed on fossilized vegetation and eggshells from the eggs in the nest and its embedding sediments indicate that this new phoenicopterid thrived under a semi-arid climate in an oligohaline (seasonally mesohaline) shallow endorheic lacustine environment. High-end microcharacterizations including SEM, TEM, and EBSD techniques were pivotal to identifying these phoenicopterid eggshells. Anatomical comparisons of the fossil bones with those of Phoenicopteriformes and Podicipediformes crown clades and extinct palaelodids confirm that this avian fossil assemblage belongs to a new and basal phoenicopterid. Conclusions/Significance Although the Podicipediformes-Phoenicopteriformes sister group relationship is now well supported, flamingos and grebes exhibit feeding, reproductive, and nesting strategies that diverge significantly. Our multi-disciplinary study is the first to reveal that the phoenicopteriform reproductive behaviour, nesting ecology and nest characteristics derived from grebe-like type strategies to reach the extremely specialized conditions observed in modern flamingo crown groups. Furthermore, our study enables us to map ecological and reproductive characters on the

  2. Antarctic Miocene Climate

    NASA Astrophysics Data System (ADS)

    Ashworth, A. C.; Lewis, A. R.

    2013-12-01

    Fossils from Antarctic Miocene terrestrial deposits, coupled with stratigraphic, geochemical and paleontological data from marine boreholes, provide new insights into the climatic history of the continent. During the Miocene, ice caps coalesced to form ice sheets and vegetated surfaces gave way to barren expanses. The cryospheric changes especially have global climatic implications. The fossil data consists of diatoms, pollen and spores, and macroscopic remains of plants, ostracods, insects, molluscs and a fish. Plant fossils include wood and leaves of Nothofagus (southern beech), seeds of several vascular plants, including Ranunculus (buttercup), Hippuris (mare's-tail) and Myriophyllum (watermilfoil), megaspores of Isoetes (quillwort), and moss species. The insect chitin consists of larval head capsules of Chironomidae (midges) and exoskeletal parts of Coleoptera (beetles). The molluscs include freshwater gastropods and bivalves. The majority of these taxa are likely descendants of taxa that had survived on the continent from the Paleogene or earlier. Even though early Miocene glaciations may have been large, the climate was never cold enough to cause the extinction of the biota, which probably survived in coastal refugia. Early Miocene (c. 20 Ma) macrofossils from the McMurdo Dry Valleys (77°S) support palynological interpretations from the Cape Roberts and ANDRILL marine records that the upland vegetation was a shrub tundra. Mean summer temperature (MST) in the uplands was c. 6°C and possibly higher at the coast. The climate was wet, supporting mires and lakes. By the mid-Miocene, even though the climate continued to be wet. MST was c. 4°C which was too cold to support Nothofagus and most vascular plant species. Stratigraphic evidence indicates that the time between the Early and Mid-Miocene was a time of repeated ice advances and retreats of small glaciers originating from ice caps. At c. 14 Ma there appears to have been a modal shift in climate to

  3. Uranium-series dating of fossil coral reefs: Extending the sea-level record beyond the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Stirling, Claudine H.; Andersen, Morten B.

    2009-07-01

    Absolutely dated records of past sea-level change are extremely important for understanding the advance and retreat of the large ice sheets. When combined with other complementary climate archives and climate models, such records offer the potential to gain an improved understanding of Earth's natural climate cycles, providing a firmer basis for assessing the role of anthropogenic effects, such as greenhouse gas emissions, in modifying climate. The U-series dating of fossil coral reefs has been widely utilized to provide absolutely dated records of past sea-level change and numerous observations now exist for the past 130,000 years spanning the last glacial cycle. Despite this, controversies still exist regarding the exact timing and character of sea-level events within this time interval, and extending the sea-level history further back in time on the basis of robust and independent age constraints for older fossil reefs remains very elusive. This is primarily due to a progressive loss in the resolution of the U-series chronometer as one goes further back in time, coupled to a lack of well-preserved, dateable coral in older fossil reefs. To overcome these limitations, the primary challenges are three-fold. First, new analytical protocols are required to improve the resolution of the U-series chronometer. Enhanced analytical precision must be coupled to accuracy through continued refinement of the U-series decay constant determinations and via the implementation of rigorous inter-laboratory calibration exercises. Second, efforts should continue to be focussed on gaining an improved understanding of the mechanisms controlling open-system exchange of the U-series isotopes in fossil reef systems. This will allow the number of 'reliable' U-series observations to be extended. Third, alternative dateable archives of past sea-level change must continue to be emphasized to further complement the coral reef database. These limitations are discussed in the context of current

  4. Non-climatic signal in ice core records: Lessons from Antarctic mega-dunes

    NASA Astrophysics Data System (ADS)

    Ekaykin, Alexey; Eberlein, Lutz; Lipenkov, Vladimir; Popov, Sergey; Schroder, Ludwig

    2015-04-01

    We present the results of glaciological investigations in the mega-dune area located 30 km to the east from Vostok Station (central East Antarctica) implemented during the 58th and 59th Russian Antarctic Expedition (January 2013 and January 2014). Snow accumulation rate and isotope content (δD and δ18O) were measured along the 2-km profile across the mega-dune ridge accompanied by precise GPS altitude measurements and GPR survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by 1 order of magnitude within the distance < 1 km, with the reduced accumulation at the leeward slope of the dune and increased accumulation in the hollow between the dunes. At the same time, the accumulation rate averaged over the length of a dune wave (25 mm w.e.) corresponds well with the value obtained at Vostok Station, which suggests no additional wind-driven snow sublimation in the mega-dunes comparing to the surrounding plateau. The snow isotope content is in negative correlation with the snow accumulation, which could be explained by post-depositional snow modification and/or by enhanced redistribution by wind of winter precipitation comparing to summer precipitation. Using the GPR data, we estimated the dune drift velocity (5.5 ± 1.3 m yr-1). The full cycle of the dune drift is thus about 340 years. Since the spatial anomalies of snow accumulation and isotope content are supposed to drift with the dune, an ice core drilled in the mega-dune area would exhibit the non-climatic 340-yr cycle of these two parameters. We made an attempt to simulate a vertical profile of isotope content with such a non-climatic variability in a virtual ice core, using the data on the dune size and velocity. The obtained results are discussed in terms of real ice core data interpretation.

  5. Cercopithecoid humeri from Taung support the distinction of major papionin clades in the South African fossil record.

    PubMed

    Gilbert, Christopher C; Takahashi, Maressa Q; Delson, Eric

    2016-01-01

    Associated cercopithecoid postcrania are rare in the Plio-Pleistocene fossil record, particularly in the case of South African karst cave sites. However, as clear postcranial differences between major papionin clades have been documented, it should be possible to assign isolated papionin postcrania to the Cercocebus/Mandrillus and Papio/Lophocebus/Theropithecus groups wherever sufficient anatomy is preserved. Here, we demonstrate that two partial humeri preserved at Taung, UCMP 56693 and UCMP 125898, are most likely attributable to the Cercocebus/Mandrillus and Papio/Lophocebus/Theropithecus clades, respectively. Univariate analyses (ANOVAs and t-tests) and multivariate analyses (discriminant function analyses) of humeral features, combined with a phylogenetic analysis of 24 humeral characters, all support our assessment. Given that the overwhelming number of craniodental specimens at Taung are attributable to two papionin taxa, Procercocebus antiquus (a member of the Cercocebus/Mandrillus clade) and Papio izodi (a purported fossil species of the modern genus Papio), we assign UCMP 56693 to Pr. antiquus and UCMP 125868 to P. izodi with a high degree of confidence. Implications for cercopithecoid evolution and biogeography are discussed, with a particular emphasis on these two fossil taxa. PMID:26767962

  6. Non-climatic signal in ice core records: lessons from Antarctic mega-dunes

    NASA Astrophysics Data System (ADS)

    Ekaykin, A.; Eberlein, L.; Lipenkov, V.; Popov, S.; Scheinert, M.; Schröder, L.; Turkeev, A.

    2015-12-01

    We present the results of glaciological investigations in the mega-dune area located 30 km to the east from Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013-January 2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the mega-dune ridge accompanied by precise GPS altitude measurements and GPR survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by one order of magnitude within the distance < 1 km, with the reduced accumulation at the leeward slope of the dune and increased accumulation in the hollow between the dunes. At the same time, the accumulation rate averaged over the length of a dune wave (22 mm we) corresponds well with the value obtained at Vostok Station, which suggests no additional wind-driven snow sublimation in the mega-dunes compared to the surrounding plateau. The snow isotopic composition is in negative correlation with the snow accumulation. Analyzing dxs/δD and 17O-excess/δD slopes, we conclude that the spatial variability of the snow isotopic composition in the mega-dune area could be explained by post-depositional snow modifications. Using the GPR data, we estimated the apparent dune drift velocity (4.6 ± 1.1 m yr-1). The full cycle of the dune drift is thus about 410 years. Since the spatial anomalies of snow accumulation and isotopic composition are supposed to drift with the dune, an ice core drilled in the mega-dune area would exhibit the non-climatic 410 year cycle of these two parameters. We simulated a vertical profile of snow isotopic composition with such a non-climatic variability, using the data on the dune size and velocity. This artificial profile is then compared with the real vertical profile of snow isotopic composition obtained from a core drilled in the mega-dune area. We

  7. Non-climatic signal in ice core records: lessons from Antarctic megadunes

    NASA Astrophysics Data System (ADS)

    Ekaykin, Alexey; Eberlein, Lutz; Lipenkov, Vladimir; Popov, Sergey; Scheinert, Mirko; Schröder, Ludwig; Turkeev, Alexey

    2016-06-01

    We present the results of glaciological investigations in the megadune area located 30 km to the east of Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013-2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the megadune ridge accompanied by precise GPS altitude measurements and ground penetrating radar (GPR) survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by 1 order of magnitude within the distance < 1 km, with the reduced accumulation at the leeward slope of the dune and increased accumulation in the hollow between the dunes. At the same time, the accumulation rate averaged over the length of a dune wave (22 mm w.e.) corresponds well with the value obtained at Vostok Station, which suggests no additional wind-driven snow sublimation in the megadunes compared to the surrounding plateau. The snow isotopic composition is in negative correlation with the snow accumulation. Analysing dxs / δD and 17O-excess / δD slopes (where dxs = δD - 8 ṡ δ18O and 17O-excess = ln(δ17O / 1000 + 1) -0.528 ṡ ln (δ18O / 1000 + 1)), we conclude that the spatial variability of the snow isotopic composition in the megadune area could be explained by post-depositional snow modifications. Using the GPR data, we estimated the apparent dune drift velocity (4.6 ± 1.1 m yr-1). The full cycle of the dune drift is thus about 410 years. Since the spatial anomalies of snow accumulation and isotopic composition are supposed to drift with the dune, a core drilled in the megadune area would exhibit the non-climatic 410-year cycle of these two parameters. We simulated a vertical profile of snow isotopic composition with such a non-climatic variability, using the data on the dune size and velocity. This artificial profile is then compared

  8. Antarctic-type blue whale calls recorded at low latitudes in the Indian and eastern Pacific Oceans

    NASA Astrophysics Data System (ADS)

    Stafford, Kathleen M.; Bohnenstiehl, DelWayne R.; Tolstoy, Maya; Chapp, Emily; Mellinger, David K.; Moore, Sue E.

    2004-10-01

    Blue whales, Balaenoptera musculus, were once abundant around the Antarctic during the austral summer, but intensive whaling during the first half of the 20th century reduced their numbers by over 99%. Although interannual variability of blue whale occurrence on the Antarctic feeding grounds was documented by whalers, little was known about where the whales spent the winter months. Antarctic blue whales produce calls that are distinct from those produced by blue whales elsewhere in the world. To investigate potential winter migratory destinations of Antarctic blue whales, we examined acoustic data for these signals from two low-latitude locales: the eastern tropical Pacific Ocean and the Indian Ocean. Antarctic-type blue whale calls were detected on hydrophones in both regions during the austral autumn and winter (May-September), with peak detections in July. Calls occurred over relatively brief periods in both oceans, suggesting that there may be only a few animals migrating so far north and/or producing calls. Antarctic blue whales appear to use both the Indian and eastern Pacific Oceans concurrently, indicating that there is not a single migratory destination. Acoustic data from the South Atlantic and from mid-latitudes in the Indian or Pacific Oceans are needed for a more global understanding of migratory patterns and destinations of Antarctic blue whales.

  9. Individual to Community-Level Faunal Responses to Environmental Change from a Marine Fossil Record of Early Miocene Global Warming

    PubMed Central

    Belanger, Christina L.

    2012-01-01

    Modern climate change has a strong potential to shift earth systems and biological communities into novel states that have no present-day analog, leaving ecologists with no observational basis to predict the likely biotic effects. Fossil records contain long time-series of past environmental changes outside the range of modern observation, which are vital for predicting future ecological responses, and are capable of (a) providing detailed information on rates of ecological change, (b) illuminating the environmental drivers of those changes, and (c) recording the effects of environmental change on individual physiological rates. Outcrops of Early Miocene Newport Member of the Astoria Formation (Oregon) provide one such time series. This record of benthic foraminiferal and molluscan community change from continental shelf depths spans a past interval environmental change (∼20.3-16.7 mya) during which the region warmed 2.1–4.5°C, surface productivity and benthic organic carbon flux increased, and benthic oxygenation decreased, perhaps driven by intensified upwelling as on the modern Oregon coast. The Newport Member record shows that (a) ecological responses to natural environmental change can be abrupt, (b) productivity can be the primary driver of faunal change during global warming, (c) molluscs had a threshold response to productivity change while foraminifera changed gradually, and (d) changes in bivalve body size and growth rates parallel changes in taxonomic composition at the community level, indicating that, either directly or indirectly through some other biological parameter, the physiological tolerances of species do influence community change. Ecological studies in modern and fossil records that consider multiple ecological levels, environmental parameters, and taxonomic groups can provide critical information for predicting future ecological change and evaluating species vulnerability. PMID:22558424

  10. Challenges Of Interpreting Antarctic Pliocene Climate From The Sediment Record At ODP Sites 693 And 697 In The Weddell Sea

    NASA Astrophysics Data System (ADS)

    OConnell, S.; Cullen, K.; Flores, C.; Hall, J. T.; Kaufman, Z. S.

    2015-12-01

    The Weddell Sea receives sediment from both East and West Antarctica and records cryospheric changes in both ice sheets. Examination of Pliocene sediment from two ODP Sites (693 and 697) provides a history of ice rafted detritus (IRD), biosilica production and orbital pacing. Age dating at both sites is limited to shipboard biostratigraphy and paleomagnetics, yielding low age resolution. Using this age data we have attempted to correlate sedimentary changes with the LR04 benthic stack to provide a context with global oceanographic changes. Site 693 is adjacent to Dronning Maud Land on a shelf bench in 2480 m water and receives sediment exclusively from the East Antarctic Ice Sheet (EAIS). Detailed analysis of Core 8R, (approximately 1 sample/2-3 kyr) within Chron 2Ar (3.58-4.18 my) shows little variation in wt% biosilica and wt% IRD (fraction >63um). The exception is around 4 Ma when IRD is relatively constant at 2 wt%, while biosilica ranges 6 to 14%. These changes do not parallel the LR04 stack, suggesting limited interaction at this site with the global ocean. 40Ar/39Ar dating of hornblendes and biotites give a consistent age between 400-650 Ma (Pan African orogeny). The limited age range and composition, as well as small variation in % of IRD and biosilica suggest a single source and support the interpretation that this portion of the EAIS was relatively stable at this time. Site 697, in 3480 m water, lies in the Jane Basin, adjacent to the South Orkney Islands. The interval between 3.0 and 3.8 Ma has higher variation in both IRD (1-13%) and biosilica (2-12%) than Site 693, an expected outcome because its terrigeneous sediment source is dominated by the less stable West Antarctic Ice Sheet. Clear obliquity pacing, correlateable with part of the LR04 stack, is observed. However after 3.3 Ma, near the beginning of the Pliocene warm period, wt% IRD is less than 2% and biosilica increases to it's highest values. This suggests that few icebergs are reaching this far

  11. A new record of post-glacial sedimentation in a glacial trough, offshore sub-Antarctic South Georgia

    NASA Astrophysics Data System (ADS)

    Meisel, Ove; Graham, Alastair; Kuhn, Gerhard

    2014-05-01

    Past studies of South Georgia's climatic history were constrained to land-based sedimentary records, such as peat bogs and coastal lakes, or to terrestrial geomorphology, such as terminal moraines. Hence, the current state of knowledge on past climatic changes in South Georgia is characterised by a complete absence of records from sedimentary marine archives in the fjords or coastal embayments of the region. This study comprises detailed examination of one of the first marine sediment cores recovered on its northeastern shelf in Royal Bay Glacial Trough. Alongside the analysis of new acoustic sub-bottom data, it is the first work to deliver extensive insight into South Georgia's post-glacial climatic history from a marine perspective. The glacial troughs on the South Georgia shelf radiate from the coast towards the shelf edge and represent major sediment traps as they form the only key large-scale depressions in the shelf bathymetry. Sedimentary records, covering a period since at least the Last Glacial Maximum, are thought likely to be recorded in most of them. The sediment core of this study covers sedimentation dated from a maximum of 15,346 ± 492 cal. yr BP until the present day. Physical core parameters indicate a major change in climatic conditions around 14,000 cal. yr BP, the time of the Antarctic Cold Reversal. Holocene climate variabilities are also recorded in the trough infill. The acoustic data show a major change in sedimentation and a pronounced unconformity at the core site, which appears to have had a widespread effect over a large area of the shelf. The origin of the unconformity remains unclear, though several hypotheses, including bottom-current erosion, glacial overriding and earthquake activity, are proposed and discussed. Another important finding at the core site is the presence of methane-derived authigenic carbonates. They form either as secondary precipitates in the subsurface or syndepositional at the seafloor as individual minerals or

  12. A new 10Be record recovered from an Antarctic ice core: validity and limitations to record the solar activity

    NASA Astrophysics Data System (ADS)

    Baroni, Mélanie; Bard, Edouard; Aster Team

    2015-04-01

    Cosmogenic nuclides provide the only possibility to document solar activity over millennia. Carbon-14 (14C) and beryllium-10 (10Be) records are retrieved from tree rings and ice cores, respectively. Recently, 14C records have also proven to be reliable to detect two large Solar Proton Events (SPE) (Miyake et al., Nature, 2012, Miyake et al., Nat. Commun., 2013) that occurred in 774-775 A.D. and in 993-994 A.D.. The origin of these events is still under debate but it opens new perspectives for the interpretation of 10Be ice core records. We present a new 10Be record from an ice core from Dome C (Antarctica) covering the last millennium. The chronology of this new ice core has been established by matching volcanic events on the WAIS Divide ice core (WDC06A) that is the best dated record in Antarctica over the Holocene (Sigl et al., JGR, 2013, Sigl et al., Nat. Clim. Change, 2014). The five minima of solar activity (Oort, Wolf, Spörer, Maunder and Dalton) are detected and characterized by a 10Be concentration increase of ca. 20% above average in agreement with previous studies of ice cores drilled at South Pole and Dome Fuji in Antarctica (Bard et al., EPSL, 1997; Horiuchi et al., Quat. Geochrono., 2008) and at NGRIP and Dye3 in Greenland (Berggren et al., GRL, 2009). The high resolution, on the order of a year, allows the detection of the 11-year solar cycle. Sulfate concentration, a proxy for volcanic eruptions, has also been measured in the very same samples, allowing a precise comparison of both 10Be and sulfate profiles. We confirm the systematic relationship between stratospheric eruptions and 10Be concentration increases, first evidenced by observations of the stratospheric volcanic eruptions of Agung in 1963 and Pinatubo in 1991 (Baroni et al., GCA, 2011). This relationship is due to an increase in 10Be deposition linked to the role played by the sedimentation of volcanic aerosols. In the light of these new elements, we will discuss the limitations and

  13. Paleoenvironmental and paleoclimatic control on early diagenetic processes and fossil record in Cretaceous continental sandstones of Brazil

    NASA Astrophysics Data System (ADS)

    Garcia, Antônio J. V.; da Rosa, Átila A. S.; Goldberg, Karin

    2005-08-01

    The Early Cretaceous, pre-rift continental rock sequences of northeastern Brazil (Rio do Peixe, Araripe, Recôncavo-Tucano, and Sergipe-Alagoas basins), deposited in a wide intracontinental basin (Afro-Brazilian Depression), and the Late Cretaceous, post-rift continental deposits of the Paraná Basin (Bauru Group, Minas Gerais) reflect the controlling processes related to the Brazilian record of nonmarine fossil vertebrates. These sequences were deposited in braided fluvial, eolian, and lacustrine environments in a semi-arid to arid climate. Sedimentary and diagenetic processes ascribed to paleoclimatic and paleoenvironmental conditions are among the major factors that control fossil preservation in fluvial deposits. The pre-rift successions contain a rare record of a dinosaur fauna that lived near more humid highlands in the northern portion of the Afro-Brazilian Depression, relative to its southern counterpart, where hardly any fossil remains would have been preserved in the adverse climatic conditions. The Afro-Brazilian Depression is interpreted as a large pathway for dinosaurs before the breakup of Gondwana. Conversely, abundant dinosaur remains (bones, eggs, and teeth) and other vertebrates (turtles, crocodiles, frogs, and fish) are found in the Bauru Group in the Paraná Basin. In this unit, the seasonal paleoclimate provided sufficient conditions for the maintenance of bodies of water that served as nesting and living sites for various vertebrate forms. Paleoclimatic conditions are assumed to account for the different preservation of bones in the Paraná Basin relative to the Afro-Brazilian Depression, because the latter was subject to more arid conditions, and the humid environment was restricted to the northern margin.

  14. Tooth counts through growth in diapsid reptiles: implications for interpreting individual and size-related variation in the fossil record.

    PubMed

    Brown, Caleb Marshall; VanBuren, Collin S; Larson, Derek W; Brink, Kirstin S; Campione, Nicolás E; Vavrek, Matthew J; Evans, David C

    2015-04-01

    Tooth counts are commonly recorded in fossil diapsid reptiles and have been used for taxonomic and phylogenetic purposes under the assumption that differences in the number of teeth are largely explained by interspecific variation. Although phylogeny is almost certainly one of the greatest factors influencing tooth count, the relative role of intraspecific variation is difficult, and often impossible, to test in the fossil record given the sample sizes available to palaeontologists and, as such, is best investigated using extant models. Intraspecific variation (largely manifested as size-related or ontogenetic variation) in tooth counts has been examined in extant squamates (lizards and snakes) but is poorly understood in archosaurs (crocodylians and dinosaurs). Here, we document tooth count variation in two species of extant crocodylians (Alligator mississippiensis and Crocodylus porosus) as well as a large varanid lizard (Varanus komodoensis). We test the hypothesis that variation in tooth count is driven primarily by growth and thus predict significant correlations between tooth count and size, as well as differences in the frequency of deviation from the modal tooth count in the premaxilla, maxilla, and dentary. In addition to tooth counts, we also document tooth allometry in each species and compare these results with tooth count change through growth. Results reveal no correlation of tooth count with size in any element of any species examined here, with the exception of the premaxilla of C. porosus, which shows the loss of one tooth position. Based on the taxa examined here, we reject the hypothesis, as it is evident that variation in tooth count is not always significantly correlated with growth. However, growth trajectories of smaller reptilian taxa show increases in tooth counts and, although current samples are small, suggest potential correlates between tooth count trajectories and adult size. Nevertheless, interspecific variation in growth patterns

  15. Vegetation response to climate change in Alaska: examples from the fossil record

    USGS Publications Warehouse

    Ager, Thomas A.

    2007-01-01

    Preface: This report was presented as an invited paper at the Fish & Wildlife Service Climate Forum held in Anchorage, Alaska on February 21-23, 2007. The purpose of the talk was to provide some examples of past climate changes that appear to have caused significant responses in Alaskan vegetation. These examples are based on interpretations of dated fossil assemblages (pollen, spores and plant macrofossils) collected and interpreted by U.S. Geological Survey and collaborating scientists from other scientific organizations during the past several decades.

  16. Revisiting the origin and diversification of vascular plants through a comprehensive Bayesian analysis of the fossil record.

    PubMed

    Silvestro, Daniele; Cascales-Miñana, Borja; Bacon, Christine D; Antonelli, Alexandre

    2015-07-01

    Plants have a long evolutionary history, during which mass extinction events dramatically affected Earth's ecosystems and its biodiversity. The fossil record can shed light on the diversification dynamics of plant life and reveal how changes in the origination-extinction balance have contributed to shaping the current flora. We use a novel Bayesian approach to estimate origination and extinction rates in plants throughout their history. We focus on the effect of the 'Big Five' mass extinctions and on estimating the timing of origin of vascular plants, seed plants and angiosperms. Our analyses show that plant diversification is characterized by several shifts in origination and extinction rates, often matching the most important geological boundaries. The estimated origin of major plant clades predates the oldest macrofossils when considering the uncertainties associated with the fossil record and the preservation process. Our findings show that the commonly recognized mass extinctions have affected each plant group differently and that phases of high extinction often coincided with major floral turnovers. For instance, after the Cretaceous-Paleogene boundary we infer negligible shifts in diversification of nonflowering seed plants, but find significantly decreased extinction in spore-bearing plants and increased origination rates in angiosperms, contributing to their current ecological and evolutionary dominance. PMID:25619401

  17. Towards a morphological metric of assemblage dynamics in the fossil record: a test case using planktonic foraminifera.

    PubMed

    Hsiang, Allison Y; Elder, Leanne E; Hull, Pincelli M

    2016-04-01

    With a glance, even the novice naturalist can tell you something about the ecology of a given ecosystem. This is because the morphology of individuals reflects their evolutionary history and ecology, and imparts a distinct 'look' to communities--making it possible to immediately discern between deserts and forests, or coral reefs and abyssal plains. Once quantified, morphology can provide a common metric for characterizing communities across space and time and, if measured rapidly, serve as a powerful tool for quantifying biotic dynamics. Here, we present and test a new high-throughput approach for analysing community shape in the fossil record using semi-three-dimensional (3D) morphometrics from vertically stacked images (light microscopic or photogrammetric). We assess the potential informativeness of community morphology in a first analysis of the relationship between 3D morphology, ecology and phylogeny in 16 extant species of planktonic foraminifera--an abundant group in the marine fossil record--and in a preliminary comparison of four assemblages from the North Atlantic. In the species examined, phylogenetic relatedness was most closely correlated with ecology, with all three ecological traits examined (depth habitat, symbiont ecology and biogeography) showing significant phylogenetic signal. By contrast, morphological trees (based on 3D shape similarity) were relatively distantly related to both ecology and phylogeny. Although improvements are needed to realize the full utility of community morphometrics, our approach already provides robust volumetric measurements of assemblage size, a key ecological characteristic. PMID:26977067

  18. Lower Cretaceous Fossil Record of The Lavrasian Continental Shelf in Northwestern Turkey and Its Correlation with Surrounding Areas

    NASA Astrophysics Data System (ADS)

    Menteş, Merve; Özkar Öngen, İzver

    2015-04-01

    This study contains Zonguldak, Amasra and Kırkalerli (İğneada) area in the Northwestern Turkey. In this region, The Istanbul-Zonguldak Composite Terrane consists of two Paleozoic terranes and their Mesozoic overstep sequences around Zonguldak and Amasra. However The Istranca Terrane is characterized by a complex nappe-pile that includes metamorphic assemblages unconformably overlain by Tertiary sediments of the Thrace basin around İğneada. The original purpose of this study to analyze fossil records of Kozlu-Zonguldak, Amasra and Kırklareli (İğneada) in which Lower Cretaceous of shallow nautical sedimentary stacking which is regarding to The Lavrasian continental shelf in Northwestern Turkey. After analysing about 90 thin section and 30 samples we followed and associated lito-biostratigraphical similarities and contrasts, horizontal and vertical variation in facies which includes Orbitolina, Neotrocholina, megalospheric Rudists and various benthic foraminifera fossil records. Correlation between sections with detailed paleontological analyse wasn't presented until today, however there are several geological examination in these areas. In accordance with this purpose, this study tries to determine possible paleogeographic borders, which are in Northwestern Anatolian of The Lavrasian continental shelf, with benthic foraminiferal assemblages . In this examination, the other aim is to correlate with researches of Lower Cretaceous continental shelf of Iranian in East, Bulgaria, Romania, Italy and Spain in West, to present comparisons and contrasts in Western Pontids. Keywords: Lower Cretaceous, Benthic Foraminifera, Correlation.

  19. Abundance Is Not Enough: The Need for Multiple Lines of Evidence in Testing for Ecological Stability in the Fossil Record

    PubMed Central

    Handley, John C.; Brett, Carlton E.

    2013-01-01

    The fossil record is the only source of information on the long-term dynamics of species assemblages. Here we assess the degree of ecological stability of the epifaunal pterioid bivalve assemblage (EPBA), which is part of the Middle Devonian Hamilton fauna of New York—the type example of the pattern of coordinated stasis, in which long intervals of faunal persistence are terminated by turnover events induced by environmental change. Previous studies have used changes in abundance structure within specific biofacies as evidence for a lack of ecological stability of the Hamilton fauna. By comparing data on relative abundance, body size, and predation, indexed as the frequency of unsuccessful shell-crushing attacks, of the EPBA, we show that abundance structure varied through time, but body-size structure and predation pressure remained relatively stable. We suggest that the energetic set-up of the Hamilton fauna's food web was able to accommodate changes in species attributes, such as fluctuating prey abundances. Ecological redundancy in prey resources, adaptive foraging of shell-crushing predators (arising from predator behavioral or adaptive switching in prey selection in response to changing prey abundances), and allometric scaling of predator-prey interactions are discussed as potential stabilizing factors contributing to the persistence of the Hamilton fauna's EPBA. Our study underscores the value and importance of multiple lines of evidence in tests of ecological stability in the fossil record. PMID:23690981

  20. Combining ice core records and ice sheet models to explore the evolution of the East Antarctic Ice sheet during the Last Interglacial period

    NASA Astrophysics Data System (ADS)

    Bradley, S. L.; Siddall, M.; Milne, G. A.; Masson-Delmotte, V.; Wolff, E.

    2013-01-01

    This study evaluates the influence of plausible changes in East Antarctic Ice sheet (EAIS) thickness and the subsequent glacio-isostatic response as a contributor to the Antarctic warming indicated by ice core records during the Last Interglacial period (LIG). These higher temperatures have been estimated primarily using the difference in the δD peak (on average ~ 15‰) in these LIG records relative to records for the Present Interglacial (PIG). Using a preliminary exploratory modelling study, it is shown that introducing a relatively moderate reduction in the amount of thickening of the EAIS over the LIG period introduces a significant increase (up to 8‰) in the predicted elevation-driven only δD signal at the central Antarctic Ice sheet (AIS) ice core sites compared to the PIG. A sensitivity test in response to a large prescribed retreat of marine-based ice in the Wilkes and Aurora subglacial basins (equivalent to ~ 7 m of global mean sea-level rise) results in a distinct elevation signal that is resolvable within the ice core stable isotope records at three sites (Taylor Dome, TALDICE and EPICA Dome C). These findings have two main implications. First, EAIS elevation's only effects could account for a significant fraction of the LIG warming interpreted from ice core records. This result highlights the need for an improved estimate to be made of the uncertainty and size of this elevation-driven δD signal which contributes to this LIG warming and that these effects need to be deconvolved prior to attempting to extract a climatic-only signal from the stable isotope data. Second, a fingerprint of significant retreat of ice in the Wilkes and Aurora basins should be detectable from ice core δD records proximal to these basins and therefore used to constrain their contribution to elevated LIG sea levels, after accounting for ice sheet-climate interactions not considered in our approach.

  1. Contrasting behavioral and feeding strategies recorded by tidal-flat bivalve trace fossils from the Upper Carboniferous of eastern Kansas

    USGS Publications Warehouse

    Mangano, M.G.; Buatois, L.A.; West, R.R.; Maples, C.G.

    1998-01-01

    Upper Carboniferous tidal-flat deposits near Waverly, eastern Kansas (Stull Shale Member, Kanwaka Shale Formation), host abundant and very well-preserved trace fossils attributed to the activity of burrowing bivalves. Thin shell lenses with an abundant bivalve fauna area associated with the ichnofossil-bearing beds and afford an unusual opportunity to relate trace fossils to their makers. Two distinctive life and feeding strategies can be reconstructed on the basis of trace fossil analysis and functional morphology. Lockeria siliquaria hyporeliefs commonly are connected with vertical to inclined, truncated endichnial shafts in the absence of horizontal locomotion traces. These structures record vertical and oblique displacement through the sediment, and suggest relatively stable domiciles rather than temporary resting traces as typically considered. Crowded bedding surfaces displaying cross-cutting relationships between specimens of L. siliquaria and differential preservation at the top (concave versus convex epireliefs) record a complex history of successive events of colonization, erosion, deposition, and recolonization (time-averaged assemblages). Irregujlar contours of some large hypichnia indicate the cast of the foot, while other outlines closely match the anterior area of Wilkingia, its suggested tracemaker. Relatively stable, vertical to inclined life positions and dominanit vertical mobility suggest a filter-feeding strategy. Moreover, the elongate shell and pallial sinus of Wilkingia providfe a strong independent line of evidence for an opisthosiphonate, moderately deep-tier inhabitant. Wilingia may represent a pioneer attempt at siphon-feeding in the late Paleozoic, preceding the outcome of the Mesozoic infaunal radiation. A second strategy is represented by Lockeia ornata and association locomotionm and locomotion/feding structures. Lockeia ornata is commonly connected with chevron locomotion traces that record the bifurcated foot of a protobranch

  2. Palaeoenvironmental records from fossil corals: The effects of submarine diagenesis on temperature and climate estimates

    NASA Astrophysics Data System (ADS)

    Allison, Nicola; Finch, Adrian A.; Webster, Jody M.; Clague, David A.

    2007-10-01

    The geochemistry of coral skeletons may reflect seawater conditions at the time of deposition and the analysis of fossil skeletons offers a method to reconstruct past climate. However the precipitation of cements in the primary coral skeleton during diagenesis may significantly affect bulk skeletal geochemistry. We used secondary ion mass spectrometry (SIMS) to measure Sr, Mg, B, U and Ba concentrations in primary coral aragonite and aragonite and calcite cements in fossil Porites corals from submerged reefs around the Hawaiian Islands. Cement and primary coral geochemistry were significantly different in all corals. We estimate the effects of cement inclusion on climate estimates from drilled coral samples, which combine cements and primary coral aragonite. Secondary 1% calcite or ˜2% aragonite cement contamination significantly affects Sr/Ca SST estimates by +1 °C and -0.4 to -0.9 °C, respectively. Cement inclusion also significantly affects Mg/Ca, B/Ca and U/Ca SST estimates in some corals. X-ray diffraction (XRD) will not detect secondary aragonite cements and significant calcite contamination may be below the limit of detection (˜1%) of the technique. Thorough petrographic examination of fossils is therefore essential to confirm that they are pristine before bulk drilled samples are analysed. To confirm that the geochemistry of the original coral structures is not affected by the precipitation of cements in adjacent pore spaces we analysed the primary coral aragonite in cemented and uncemented areas of the skeleton. Sr/Ca, B/Ca and U/Ca of primary coral aragonite is not affected by the presence of cements in adjacent interskeletal pore spaces i.e. the coral structures maintain their original composition and selective SIMS analysis of these structures offers a route to the reconstruction of accurate SSTs from altered coral skeletons. However, Mg/Ca and Ba/Ca of primary coral aragonite are significantly higher in parts of skeletons infilled with high Mg

  3. Late glacial climate estimates for southern Nevada: The ostracode fossil record

    SciTech Connect

    Forester, R.M.; Smith, A.J.

    1995-10-01

    Climate change plays an important role in determining as possible long term hydrological performance of the potential high level nuclear waste repository within Yucca Mountain, Nevada. Present-day global circulation results in this region having an arid to semi-arid climate characterized by hot and relatively dry summers. Global circulation during the late glacial (about 14 to 20 ka) was very different from the present-day. Preliminary study of late-glacial fossil ostracodes from {open_quotes}marsh deposits{close_quotes} in the upper Las Vegas Valley suggests mean annual precipitation may have been four times higher, while mean annual temperature may have been about 10{degrees}C cooler than today. A major difference between present-day and late-glacial climate was likely the existence of cooler, cloudier, and wetter summers in the past.

  4. Late Miocene terrestrial record of East Antarctic Ice Sheet configuration and dynamics recorded by volcanic lithofacies and sequence characteristics in northern Victoria Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Smellie, John; Rocchi, Sergio; Gemelli, Maurizio; di Vincenzo, Gianfranco; Armienti, Pietro

    2010-05-01

    Late Miocene (c. 12-5 Ma) volcanic sequences crop out extensively along > 250 km of northern Victoria Land coastline, at the Ross Sea margin of the East Antarctic Ice Sheet (EAIS). The sequences are dominantly glaciovolcanic and two main types are present. The commonest and most representative comprises multiple mafic aa lava-fed deltas, a type of glaciovolcanic sequence not previously described. The second sequence type resembles mafic glaciovolcanic sheet-like sequences of Mt Pinafore type (sensu Smellie, 2006, Earth-Science Reviews, 74, 241-268) but includes felsic examples as well, and there are additional minor occurrences of pyroclastic cones and an ice-marginal lacustrine deposit. Interpretation of the glaciovolcanic sequences enables estimates of past ice thicknesses that were coeval with eruptions to be made with considerable certainty. The sequences were formed in association with a glacial cover that was typically, and probably never much more than, a few hundred metres thick. Despite gaps in the record, no evidence was observed for subaerial (i.e. fully ice-free) eruptive conditions, suggesting either that ice-free conditions did not occur or else were of such short duration that they left no record. These observations are consistent with the presence of a late Miocene ice dome or regional ice sheet situated in northern Victoria Land for the period, although it may have been confluent with the EAIS similar to conditions present today. The basal glacial thermal regime varied from wet-based and dynamic, to cold-based (frozen to its bed) and presumably relatively stable. A major change from wet-based ice to cold-based ice is evident but its timing is not precisely determined. There is also evidence that temporary changes in thermal regime might have occurred before and after the principal transition.

  5. Microbe-like inclusions in tree resins and implications for the fossil record of protists in amber.

    PubMed

    Thiel, V; Lausmaa, J; Sjövall, P; Ragazzi, E; Seyfullah, L J; Schmidt, A R

    2016-07-01

    During the past two decades, a plethora of fossil micro-organisms have been described from various Triassic to Miocene ambers. However, in addition to entrapped microbes, ambers commonly contain microscopic inclusions that sometimes resemble amoebae, ciliates, microfungi, and unicellular algae in size and shape, but do not provide further diagnostic features thereof. For a better assessment of the actual fossil record of unicellular eukaryotes in amber, we studied equivalent inclusions in modern resin of the Araucariaceae; this conifer family comprises important amber-producers in Earth history. Using time-of-flight secondary ion mass spectrometry (ToF-SIMS), we investigated the chemical nature of the inclusion matter and the resin matrix. Whereas the matrix, as expected, showed a more hydrocarbon/aromatic-dominated composition, the inclusions contain abundant salt ions and polar organics. However, the absence of signals characteristic for cellular biomass, namely distinctive proteinaceous amino acids and lipid moieties, indicates that the inclusions do not contain microbial cellular matter but salts and hydrophilic organic substances that probably derived from the plant itself. Rather than representing protists or their remains, these microbe-like inclusions, for which we propose the term 'pseudoinclusions', consist of compounds that are immiscible with the terpenoid resin matrix and were probably secreted in small amounts together with the actual resin by the plant tissue. Consequently, reports of protists from amber that are only based on the similarity of the overall shape and size to extant taxa, but do not provide relevant features at light-microscopical and ultrastructural level, cannot be accepted as unambiguous fossil evidence for these particular groups. PMID:27027519

  6. Uncertainties in dating constrain model choice for inferring extinction time from fossil records

    NASA Astrophysics Data System (ADS)

    Saltré, Frédérik; Brook, Barry W.; Rodríguez-Rey, Marta; Cooper, Alan; Johnson, Christopher N.; Turney, Chris S. M.; Bradshaw, Corey J. A.

    2015-03-01

    Accurate estimates of the timing of extinctions (θ) are critical for understanding the causes of major die-off events and for identifying evolutionary or environmental transitions. Yet many studies have demonstrated that sampling biases and underlying statistical assumptions affect the accuracy of model-based estimates of extinction times (θˆ), and the added uncertainty contributed by inherent (laboratory) dating errors has largely been neglected. Here we provide a general guide (model-selection key) for choosing from among eight alternative ';frequentist sampling' (i.e., non-Bayesian) methods, differentiated by their treatment of both the probability of record occurrence and uncertainties in record dates, the most appropriate for a given record. We first provide a methodological framework to characterize time series of dated records as a function of the number of records, the size of the interval between successive records, and laboratory dating errors. Using both simulated data and dated Australian megafauna remains, we then assess how the characteristic of a dataset's time series dictates model performance and the probability of misclassification (false extant vs. false extinct). Among the four classic frequentist methods providing highest model performance, Marshall's (1997) and McCarthy's (1998) methods have the highest model precision. However, high model performance did not prevent misclassification errors, such that the Gaussian-resampled inverse-weighted McInerny (GRIWM) approach is the only method providing both high model accuracy and no misclassification issues, because of its unique down-weighting interval procedure and its ability to account for uncertainties in record dates. Applying the guideline to three time series of extinct Australian species, we recommend using Marshall's, McCarthy's and/or GRIWM methods to infer θ of both Thylacinus sp. and Genyornis sp., because each dataset is characterized by many sightings and a low variance of the

  7. Fossil Horses

    NASA Astrophysics Data System (ADS)

    MacFadden, Bruce J.

    1994-06-01

    The family Equidae have an extensive fossil record spanning the past 58 million years, and the evolution of the horse has frequently been used as a classic example of long-term evolution. In recent years, however, there have been many important discoveries of fossil horses, and these, in conjunction with such new methods as cladistics, and techniques such as precise geochronology, have allowed us to achieve a much greater understanding of the evolution and biology of this important group. This book synthesizes the large body of data and research relevant to an understanding of fossil horses from several disciplines including biology, geology and paleontology. Using horses as the central theme, the author weaves together in the text such topics as modern geochronology, paleobiogeography, climate change, evolution and extinction, functional morphology, and population biology during the Cenozoic period. This book will be exciting reading for researchers and graduate students in vertebrate paleontology, evolution, and zoology.

  8. Observations of asexual reproductive strategies in Antarctic hexactinellid sponges from ROV video records

    NASA Astrophysics Data System (ADS)

    Teixidó, Núria; Gili, Josep-Maria; Uriz, María-J.; Gutt, Julian; Arntz, Wolf E.

    2006-04-01

    Hexactinellid sponges are one of the structuring taxa of benthic communities on the Weddell Sea shelf (Antarctica). However, little is known about their reproduction patterns (larval development, release, settlement, and recruitment), particularly in relation to sexual and asexual processes in sponge populations. Video stations obtained during several expeditions covering a wide depth range and different areas recorded a high frequency of asexual reproductive strategies (ARS) (bipartition and budding) among hexactinellids. Analysis of seabed video strips between 108 and 256 m depth, representing an area of 1400 m 2, showed that about 28% of these sponges exhibited ARS. The Rossella nuda type dominated most of the video stations and exhibited the highest proportion of budding (35%). This proportion increased with the size class. Size class >20 cm exhibited in all the stations a mean value of 8.3±0.7 (SE) for primary and of 2.5±0.2 (SE) for secondary propagules per sponge, respectively. Results from a shallow station (Stn 059, 117 m depth) showed the highest relative abundance of R. nuda type and budding (>20 cm ˜72%, 10-20 cm ˜60%, 5-10 cm ˜12%, and <5 cm ˜3%). A potential influence of iceberg scouring disturbance on the occurrence of budding and number of propagules also was investigated. We conclude that asexual reproduction in hexactinellid sponges may be more frequent than has been thought before and it may greatly influence the genetic structure of populations.

  9. Diagnose oscillation properties observed in an Antarctic ice core oxygen isotope record

    NASA Astrophysics Data System (ADS)

    Motizuki, Y.

    2013-12-01

    We investigate water isotope ratio profile obtained in a shallow ice core drilled at Dome Fuji, East Antarctica. Two sets of time series will be discussed; the first set was analyzed at NIPR (National Institute of Polar Research) with temporal resolution of about 5 years for the past 1900 years, and the second was obtained at RIKEN very recently with temporal resolution of less than a year for the past 400 years. Paying our attention on uncertainty in the depth-age relation, time series analyses to the measured oxygen isotope variations will be presented. A preliminary result for the former time series shows a ~200-year periodicity, which is by chance the same with one of solar activity cycles reported from tree ring studies. We note that snow and ice core samples obtained at Dome Fuji are known to contain much information on the stratosphere than those recovered from other sites in both the hemisphere. Considering this, we will further discuss possible mechanism to cause oscillation in oxygen isotope record in a Dome Fuji ice core.

  10. Towards a morphological metric of assemblage dynamics in the fossil record: a test case using planktonic foraminifera

    PubMed Central

    Hsiang, Allison Y.; Elder, Leanne E.; Hull, Pincelli M.

    2016-01-01

    With a glance, even the novice naturalist can tell you something about the ecology of a given ecosystem. This is because the morphology of individuals reflects their evolutionary history and ecology, and imparts a distinct ‘look’ to communities—making it possible to immediately discern between deserts and forests, or coral reefs and abyssal plains. Once quantified, morphology can provide a common metric for characterizing communities across space and time and, if measured rapidly, serve as a powerful tool for quantifying biotic dynamics. Here, we present and test a new high-throughput approach for analysing community shape in the fossil record using semi-three-dimensional (3D) morphometrics from vertically stacked images (light microscopic or photogrammetric). We assess the potential informativeness of community morphology in a first analysis of the relationship between 3D morphology, ecology and phylogeny in 16 extant species of planktonic foraminifera—an abundant group in the marine fossil record—and in a preliminary comparison of four assemblages from the North Atlantic. In the species examined, phylogenetic relatedness was most closely correlated with ecology, with all three ecological traits examined (depth habitat, symbiont ecology and biogeography) showing significant phylogenetic signal. By contrast, morphological trees (based on 3D shape similarity) were relatively distantly related to both ecology and phylogeny. Although improvements are needed to realize the full utility of community morphometrics, our approach already provides robust volumetric measurements of assemblage size, a key ecological characteristic. PMID:26977067

  11. Late Eocene Antarctic glacial events revealed by radiogenic isotope records from the Kerguelen Plateau

    NASA Astrophysics Data System (ADS)

    Smith, B. W.; Munn, G. H.; Bohaty, S. M.; Scher, H. D.

    2011-12-01

    Oxygen isotope measurements of benthic foraminifera in ODP Hole 738B (Kerguelen Plateau, Southern Ocean) show a 0.6% shift toward more positive values at ca. 37.1 Ma, near the middle/late Eocene boundary. The δ18O values during this cool event reach 2.2%, which may reflect a combination of both intermediate deep-water cooling and partial glaciation of East Antarctica. We conducted neodymium (Nd) isotope measurements of the terrigenous detrital fraction (i.e., decarbonated and leached) from the same samples used to construct the stable isotope record. Our results reveal a shift in the Nd isotope composition of fine-grained material deposited on Kerguelen Plateau that coincides with the δ18O excursion. The background ɛNd values (i.e., before and after the δ18O shift) are -12 ɛNd, consistent with regionally sourced sediment from along the East Antarctica margin (e.g., Wilkes Land, Prydz Bay). During the δ18O excursion at 37.1 Ma, there is transient decrease in ɛNd values to -15.5. These results strongly indicate that Kerguelen Plateau received an influx of detrital material from ancient sediment sources (i.e., with low ɛNd values), such as those found in nearby Prydz Bay. Our results support an increase in continental ice volume in East Antarctica during this event, resulting in enhanced rates of mechanical weathering. We have also documented a second cool event ca. 36.7 Ma, approximately 400 kyr after the 37 Ma event. Future efforts will focus on determining the timing of middle-to-late Eocene cooling episoides and further documenting changes in weathering during each of these events.

  12. High-resolution leaf-fossil record spanning the Cretaceous/Tertiary boundary

    USGS Publications Warehouse

    Johnson, K.R.; Nichols, D.J.; Attrep, M., Jr.; Orth, C.J.

    1989-01-01

    THEORIES that explain the extinctions characterizing the Cretaceous/Tertiary (K/T) boundary1-3 need to be tested by analyses of thoroughly sampled biotas. Palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction4-12, but have not been combined with quantitative analyses of fossil leaves (megaflora). Megafloral studies complement palynology by representing local floras with assemblages capable of high taxonomic resolution13, but have previously lacked the sample size and stratigraphic spacing needed to resolve latest Cretaceous floral history5,14-18. We have now combined megafloral data from a 100-m-thick composite K/T boundary section in North Dakota with detailed palynological analysis. Here the boundary is marked by a 30% palynofloral extinction coincident with iridium and shocked-mineral anomalies and lies ???2 m above the highest dinosaur remains. The megaflora undergoes a 79% turnover across the boundary, and smaller changes 17- and 25-m below it. This pattern is consistent with latest Cretaceous climatic warming preceding a bolide impact. ?? 1989 Nature Publishing Group.

  13. Biophysical constraints on the origin of leaves inferred from the fossil record

    PubMed Central

    Osborne, C. P.; Beerling, D. J.; Lomax, B. H.; Chaloner, W. G.

    2004-01-01

    The molecular tool kit for producing flat-bladed photosynthetic structures evolved in marine and terrestrial plants during the middle Paleozoic, but it took a further 20 million years before leaves suddenly spread throughout land floras. This delay has long been difficult to explain, given the apparent advantage of leaves for photosynthetic primary production. Theory and experiments predict that exceptionally high atmospheric CO2 levels in the middle Paleozoic delayed the origin of leaves by restricting stomatal development. This would have limited evaporative cooling, leading to lethal overheating of leaves absorbing large quantities of solar energy. Here we test the central prediction of this argument with a morphometric analysis of 300 plant fossils from major European collections. We show a 25-fold enlargement of leaf blades in two phylogenetically independent clades as atmospheric CO2 levels fell during the late Paleozoic. Furthermore, preliminary data suggest that the first abrupt increase in leaf size was accompanied by an 8-fold rise in stomatal density. These evolutionary patterns support the relaxation of biophysical constraints on leaf area predicted by theory and point to a significant role for CO2 in plant evolution. PMID:15240879

  14. Fossil pollen records indicate that Patagonian desertification was not solely a consequence of Andean uplift.

    PubMed

    Palazzesi, L; Barreda, V D; Cuitiño, J I; Guler, M V; Tellería, M C; Ventura Santos, R

    2014-01-01

    The Patagonian steppe-a massive rain-shadow on the lee side of the southern Andes-is assumed to have evolved ~15-12 Myr as a consequence of the southern Andean uplift. However, fossil evidence supporting this assumption is limited. Here we quantitatively estimate climatic conditions and plant richness for the interval ~10-6 Myr based on the study and bioclimatic analysis of terrestrially derived spore-pollen assemblages preserved in well-constrained Patagonian marine deposits. Our analyses indicate a mesothermal climate, with mean temperatures of the coldest quarter between 11.4 °C and 16.9 °C (presently ~3.5 °C) and annual precipitation rarely below 661 mm (presently ~200 mm). Rarefied richness reveals a significantly more diverse flora during the late Miocene than today at the same latitude but comparable with that approximately 2,000 km further northeast at mid-latitudes on the Brazilian coast. We infer that the Patagonian desertification was not solely a consequence of the Andean uplift as previously insinuated. PMID:24675482

  15. Fossil pollen records indicate that Patagonian desertification was not solely a consequence of Andean uplift

    NASA Astrophysics Data System (ADS)

    Palazzesi, L.; Barreda, V. D.; Cuitiño, J. I.; Guler, M. V.; Tellería, M. C.; Ventura Santos, R.

    2014-03-01

    The Patagonian steppe—a massive rain-shadow on the lee side of the southern Andes—is assumed to have evolved ~15-12 Myr as a consequence of the southern Andean uplift. However, fossil evidence supporting this assumption is limited. Here we quantitatively estimate climatic conditions and plant richness for the interval ~10-6 Myr based on the study and bioclimatic analysis of terrestrially derived spore-pollen assemblages preserved in well-constrained Patagonian marine deposits. Our analyses indicate a mesothermal climate, with mean temperatures of the coldest quarter between 11.4 °C and 16.9 °C (presently ~3.5 °C) and annual precipitation rarely below 661 mm (presently ~200 mm). Rarefied richness reveals a significantly more diverse flora during the late Miocene than today at the same latitude but comparable with that approximately 2,000 km further northeast at mid-latitudes on the Brazilian coast. We infer that the Patagonian desertification was not solely a consequence of the Andean uplift as previously insinuated.

  16. International Workshop on Antarctic Meteorites

    NASA Technical Reports Server (NTRS)

    Annexstad, J. O.; Schultz, L.; Waenke, H.

    1986-01-01

    Topics addressed include: meteorite concentration mechanisms; meteorites and the Antarctic ice sheet; iron meteorites; iodine overabundance in meteorites; entrainment, transport, and concentration of meteorites in polar ice sheets; weathering of stony meteorites; cosmic ray records; radiocarbon dating; element distribution and noble gas isotopic abundances in lunar meteorites; thermoanalytical characterization; trace elements; thermoluminescence; parent sources; and meteorite ablation and fusion spherules in Antarctic ice.

  17. The Cenozoic history of East Antarctic subglacial erosion and sediment flux from the offshore detrital thermochronometric record

    NASA Astrophysics Data System (ADS)

    Thomson, S. N.; Reiners, P. W.; Tochilin, C. J.; Hemming, S. R.; Gehrels, G. E.

    2011-12-01

    To improve and better quantify the record of subglacial erosion and landscape evolution in East Antarctica since the inception of the East Antarctic ice sheet (EAIS) at 34 Ma we have developed a novel technique to triple-date single grains of detrital apatite by U-Pb, fission track, and (U-Th)/He dating. We applied this method to offshore sediments deposited from the Cretaceous through Holocene in Prydz Bay. The modern source region of Prydz Bay incorporates the Lambert Glacier catchment that drains some 20% of the EAIS. In pre-glacial times, landscape reconstructions and sediment analysis imply that Prydz Bay was the site of deposition of fluvial sediments draining large parts of the East Antarctic craton including parts of the now-subglacial Gamburtsev Mountains. Apatite U-Pb ages from samples through the whole stratigraphic section show a dominant Pan-African age signature (ca. 500 Ma) implying much of the Lambert catchment experienced Pan-African metamorphism to temperatures > ca. 500°C. Pre-glacial Late Cretaceous and Eocene fluvial sandstones are characterized by old apatite fission track (AFT) and (U-Th)/He (AHe) ages between about 300 and 220 Ma. AFT and AHe single grain age pairs show two distinct groups, one indicative of fast cooling and erosion during the Permian followed by residence at low near-surface temperatures until the Eocene, and the other indicative of more constant, but very slow erosion rates (<0.02 km/Myr) since the Permian. A few ages between 110-120 Ma are seen in some Late Cretaceous sediments diagnostic of resetting related to local basic magmatism associated with Kerguelen plume activity seen in very localized catchment bedrock exposures. Importantly, our thermochronometric data from pre-glacial (Eocene and older) sediments show no evidence for any enhanced Cretaceous erosion in the Lambert Graben catchment area, despite the almost certain presence of the >2500 m high Gamburtsev mountains. These old ages are indicative of a slowly

  18. THE VERY FAINT END OF THE UV LUMINOSITY FUNCTION OVER COSMIC TIME: CONSTRAINTS FROM THE LOCAL GROUP FOSSIL RECORD

    SciTech Connect

    Weisz, Daniel R.; Johnson, Benjamin D.; Conroy, Charlie

    2014-10-10

    We present a new technique to estimate the evolution of the very faint end of the UV luminosity function (LF) out to z ∼ 5. Measured star formation histories (SFHs) from the fossil record of Local Group (LG) galaxies are used to reconstruct the LF down to M {sub UV} ∼–5 at z ∼ 5 and M {sub UV} ∼–1.5 at z < 1. Such faint limits are well beyond the current observational limits and are likely to remain beyond the limits of next-generation facilities. The reconstructed LFs, when combined with direct measurements of the LFs at higher luminosity, are well-fit by a standard Schechter function with no evidence of a break to the faintest limits probed by this technique. The derived faint-end slope, α, steepens from ≈ – 1.2 at z < 1 to ≈ – 1.6 at 4 < z < 5. We test the effects of burstiness in the SFHs and find the recovered LFs to be only modestly affected. Incompleteness corrections for the faintest LG galaxies and the (unlikely) possibility of significant luminosity-dependent destruction of dwarf galaxies between high redshift and the present epoch are important uncertainties. These and other uncertainties can be mitigated with more detailed modeling and future observations. The reconstructed faint end LF from the fossil record can therefore be a powerful and complementary probe of the high-redshift faint galaxies believed to play a key role in the reionization of the universe.

  19. The fossil record of phenotypic integration and modularity: A deep-time perspective on developmental and evolutionary dynamics

    PubMed Central

    Goswami, Anjali; Binder, Wendy J.; Meachen, Julie; O’Keefe, F. Robin

    2015-01-01

    Variation is the raw material for natural selection, but the factors shaping variation are still poorly understood. Genetic and developmental interactions can direct variation, but there has been little synthesis of these effects with the extrinsic factors that can shape biodiversity over large scales. The study of phenotypic integration and modularity has the capacity to unify these aspects of evolutionary study by estimating genetic and developmental interactions through the quantitative analysis of morphology, allowing for combined assessment of intrinsic and extrinsic effects. Data from the fossil record in particular are central to our understanding of phenotypic integration and modularity because they provide the only information on deep-time developmental and evolutionary dynamics, including trends in trait relationships and their role in shaping organismal diversity. Here, we demonstrate the important perspective on phenotypic integration provided by the fossil record with a study of Smilodon fatalis (saber-toothed cats) and Canis dirus (dire wolves). We quantified temporal trends in size, variance, phenotypic integration, and direct developmental integration (fluctuating asymmetry) through 27,000 y of Late Pleistocene climate change. Both S. fatalis and C. dirus showed a gradual decrease in magnitude of phenotypic integration and an increase in variance and the correlation between fluctuating asymmetry and overall integration through time, suggesting that developmental integration mediated morphological response to environmental change in the later populations of these species. These results are consistent with experimental studies and represent, to our knowledge, the first deep-time validation of the importance of developmental integration in stabilizing morphological evolution through periods of environmental change. PMID:25901310

  20. Novel long-chain anteiso-alkanes and anteiso-alkanoic acids in Antarctic rocks colonized by living and fossil cryptoendolithic microorganisms

    NASA Technical Reports Server (NTRS)

    Matsumoto, G. I.; Friedmann, E. I.; Watanuki, K.; Ocampo-Friedmann, R.

    1992-01-01

    Saponified extracts of rock samples colonized by cryptoendolithic microbial communities from the McMurdo Dry Valleys of Southern Victoria Land, Antarctica, were separated into hydrocarbon and fatty acid fractions by silica gel column chromatography. Hydrocarbons and methyl esters of fatty acids were analyzed by capillary gas chromatography-mass spectrometry. Unusually, a suite of long-chain anteiso-alkanes (a-C20 to a-C30) and anteiso-alkanoic acids (a-C20 to a-C30) were detected in many samples, together with straight-chain, branched and/or cyclic and acyclic isoprenoid compounds. These novel compounds are probably derived from unidentified heterotrophic bacteria or symbiotic processes in a unique microbial community in the Antarctic cold desert and suggest the occurrence of a special biosynthetic pathway. Long-chain anteiso-alkanes are probably formed through microbial decarboxylation of corresponding anteiso-alkanoic acids. They may serve as new biomarkers in environmental and geochemical studies.

  1. Neotropical mammal diversity and the Great American Biotic Interchange: spatial and temporal variation in South America's fossil record

    PubMed Central

    Carrillo, Juan D.; Forasiepi, Analía; Jaramillo, Carlos; Sánchez-Villagra, Marcelo R.

    2015-01-01

    The vast mammal diversity of the Neotropics is the result of a long evolutionary history. During most of the Cenozoic, South America was an island continent with an endemic mammalian fauna. This isolation ceased during the late Neogene after the formation of the Isthmus of Panama, resulting in an event known as the Great American Biotic Interchange (GABI). In this study, we investigate biogeographic patterns in South America, just before or when the first immigrants are recorded and we review the temporal and geographical distribution of fossil mammals during the GABI. We performed a dissimilarity analysis which grouped the faunal assemblages according to their age and their geographic distribution. Our data support the differentiation between tropical and temperate assemblages in South America during the middle and late Miocene. The GABI begins during the late Miocene (~10–7 Ma) and the putative oldest migrations are recorded in the temperate region, where the number of GABI participants rapidly increases after ~5 Ma and this trend continues during the Pleistocene. A sampling bias toward higher latitudes and younger records challenges the study of the temporal and geographic patterns of the GABI. PMID:25601879

  2. Tectonometamorphic record in a fossilized subduction channel: insights from the Cycladic Blueschist Unit (Cyclades, Greece)

    NASA Astrophysics Data System (ADS)

    Laurent, Valentin; Roche, Vincent; Jolivet, Laurent; Lanari, Pierre; Augier, Romain; Scaillet, Stéphane

    2016-04-01

    The comprehension of subduction dynamics is partly based on the reconstruction of detailed Pressure-Temperature-time-deformation paths of HP-LT metamorphic rocks, which have undergone a complete burial-exhumation cycle. The Cycladic Blueschist Unit (CBU), located in the Aegean domain (Greece), is one of the best examples of a fossilized subduction channel. The tectonometamorphic history of this domain can be summarized in two successive episodes: (1) From the Paleocene to the Eocene, the formation of the Hellenides-Taurides belt due to the convergence between Eurasia and Africa. During this episode, the entrance of the Apulian crust in the subduction zone led to an episode of crustal thickening and formation-exhumation of HP-LT metamorphic units like the CBU. (2) From the Early Oligocene, consecutively to the retreat of the African slab, back-arc extension affected the previously thickened crust and the Aegean Sea started to form. Syros and Sifnos islands are worldwide known for their excellent preservation of HP-LT parageneses in the CBU, providing one of the best case-studies to understand the tectonometamorphic evolution of a subduction channel. This study aims to decipher the P-T-t-d path of the CBU using for the first time on Syros, Raman spectroscopy of carbonaceous material to constrain metamorphic peak temperature (Beyssac et al., 2002) and a quantitative X-ray micro-mapping approach together with the program XMapTools (Lanari et al., 2014). The micro-mapping tools allowed extracting local chemical compositions observed in zoned garnets to calculate the local effective bulk composition. Forward models are then created to constrain P-T conditions of crystallization of these local assemblages. This study brings new data on the debated metamorphic peak conditions of the CBU, which undoubtedly attained at least 20 ± 2 kbar / 530 ± 50°C. Additionally, the geological and metamorphic maps of Syros and Sifnos have been totally redrawn in order to decipher the

  3. Shifts in Ross Sea food web structure as indicated by δ15N and δ13C values of fossil Antarctic seals

    NASA Astrophysics Data System (ADS)

    Leopold, A.; Brault, E.; McMahon, K.

    2013-12-01

    As climate change continues to mount, there is a growing need for understanding its effects on biological-physical interactions of marine ecosystems. Assessing the effects of anthropogenic activities on the coastal marine ecosystem involves understanding the underlying mechanisms driving these changes as well as establishing baselines of the natural system. Preliminary findings have indicated shifts in bulk carbon (C) and nitrogen (N) isotopic values of southern elephant seal (Mirounga leonina) samples, collected in the Dry Valleys of Antarctica in the Ross Sea region, over approximately the last 7,000 years. These shifts could result from 1) seals changing their foraging location and/or diet over this time, 2) climate change-induced shifts in the biogeochemistry at the base of the food web, or 3) some combination of both processes. We explored the patterns of long-term change in Ross Sea food web structure by examining the stable isotope values of three top predators in this system, Weddell seals (Leptonychotes weddellii), leopard seals (Hydrurga leptonyx), and crabeater seals (Lobodon carcinophagus). Fossil seal samples were collected in the Dry Valleys during the austral summer of 2012/13 and then analyzed for bulk C and N isotopes via an elemental analyzer/isotope-ratio mass spectrometer (EA/IRMS). Our initial findings indicate that C isotopic values of fossil seal samples from Weddell, leopard, and crabeater seals were more enriched than isotopic values of modern seals of the same species (e.g., δ13C = -22.79 × 0.92 ‰ and -26.71 × 0.50 ‰ for fossil and modern crabeater seals, respectively). Given the relatively consistent diet of crabeater seals, these findings suggest a shift in baseline food web structure occurred over the last 10,000 years, either through changes in foraging location or local shifts in biogeochemistry. For all species, N isotopic values are widely variable (e.g., 7.28 to 16.0 δ15N ‰ for the Weddell seal), which may be a result of

  4. Arthropod eyes: The early Cambrian fossil record and divergent evolution of visual systems.

    PubMed

    Strausfeld, Nicholas J; Ma, Xiaoya; Edgecombe, Gregory D; Fortey, Richard A; Land, Michael F; Liu, Yu; Cong, Peiyun; Hou, Xianguang

    2016-03-01

    evolution of sessile eyes equipped with optics typical of extant xiphosurans. Observations of fossil material, including that of trilobites and eurypterids, support the proposition that the ancestral compound eye was the apposition type. Cambrian arthropods include possible precursors of mandibulate eyes. The latter are the modified compound eyes, now sessile, and their underlying optic lobes exemplified by scutigeromorph chilopods, and the mobile stalked compound eyes and more elaborate optic lobes typifying Pancrustacea. Radical divergence from an ancestral apposition type is demonstrated by the evolution of chelicerate eyes, from doublet sessile-eyed stem-group taxa to special apposition eyes of xiphosurans, the compound eyes of eurypterids, and single-lens eyes of arachnids. Different eye types are discussed with respect to possible modes of life of the extinct species that possessed them, comparing these to extant counterparts and the types of visual centers the eyes might have served. PMID:26276096

  5. When did Carcharocles megalodon become extinct? A new analysis of the fossil record.

    PubMed

    Pimiento, Catalina; Clements, Christopher F

    2014-01-01

    Carcharocles megalodon ("Megalodon") is the largest shark that ever lived. Based on its distribution, dental morphology, and associated fauna, it has been suggested that this species was a cosmopolitan apex predator that fed on marine mammals from the middle Miocene to the Pliocene (15.9-2.6 Ma). Prevailing theory suggests that the extinction of apex predators affects ecosystem dynamics. Accordingly, knowing the time of extinction of C. megalodon is a fundamental step towards understanding the effects of such an event in ancient communities. However, the time of extinction of this important species has never been quantitatively assessed. Here, we synthesize the most recent records of C. megalodon from the literature and scientific collections and infer the date of its extinction by making a novel use of the Optimal Linear Estimation (OLE) model. Our results suggest that C. megalodon went extinct around 2.6 Ma. Furthermore, when contrasting our results with known ecological and macroevolutionary trends in marine mammals, it became evident that the modern composition and function of modern gigantic filter-feeding whales was established after the extinction of C. megalodon. Consequently, the study of the time of extinction of C. megalodon provides the basis to improve our understanding of the responses of marine species to the removal of apex predators, presenting a deep-time perspective for the conservation of modern ecosystems. PMID:25338197

  6. When Did Carcharocles megalodon Become Extinct? A New Analysis of the Fossil Record

    PubMed Central

    Pimiento, Catalina; Clements, Christopher F.

    2014-01-01

    Carcharocles megalodon (“Megalodon”) is the largest shark that ever lived. Based on its distribution, dental morphology, and associated fauna, it has been suggested that this species was a cosmopolitan apex predator that fed on marine mammals from the middle Miocene to the Pliocene (15.9–2.6 Ma). Prevailing theory suggests that the extinction of apex predators affects ecosystem dynamics. Accordingly, knowing the time of extinction of C. megalodon is a fundamental step towards understanding the effects of such an event in ancient communities. However, the time of extinction of this important species has never been quantitatively assessed. Here, we synthesize the most recent records of C. megalodon from the literature and scientific collections and infer the date of its extinction by making a novel use of the Optimal Linear Estimation (OLE) model. Our results suggest that C. megalodon went extinct around 2.6 Ma. Furthermore, when contrasting our results with known ecological and macroevolutionary trends in marine mammals, it became evident that the modern composition and function of modern gigantic filter-feeding whales was established after the extinction of C. megalodon. Consequently, the study of the time of extinction of C. megalodon provides the basis to improve our understanding of the responses of marine species to the removal of apex predators, presenting a deep-time perspective for the conservation of modern ecosystems. PMID:25338197

  7. Reorganization of Southern Ocean plankton ecosystem at the onset of Antarctic glaciation.

    PubMed

    Houben, Alexander J P; Bijl, Peter K; Pross, Jörg; Bohaty, Steven M; Passchier, Sandra; Stickley, Catherine E; Röhl, Ursula; Sugisaki, Saiko; Tauxe, Lisa; van de Flierdt, Tina; Olney, Matthew; Sangiorgi, Francesca; Sluijs, Appy; Escutia, Carlota; Brinkhuis, Henk; Dotti, Carlota Escutia; Klaus, Adam; Fehr, Annick; Williams, Trevor; Bendle, James A P; Carr, Stephanie A; Dunbar, Robert B; Flores, José-Abel; Gonzàlez, Jhon J; Hayden, Travis G; Iwai, Masao; Jimenez-Espejo, Francisco J; Katsuki, Kota; Kong, Gee Soo; McKay, Robert M; Nakai, Mutsumi; Pekar, Stephen F; Riesselman, Christina; Sakai, Toyosaburo; Salzmann, Ulrich; Shrivastava, Prakash K; Tuo, Shouting; Welsh, Kevin; Yamane, Masako

    2013-04-19

    The circum-Antarctic Southern Ocean is an important region for global marine food webs and carbon cycling because of sea-ice formation and its unique plankton ecosystem. However, the mechanisms underlying the installation of this distinct ecosystem and the geological timing of its development remain unknown. Here, we show, on the basis of fossil marine dinoflagellate cyst records, that a major restructuring of the Southern Ocean plankton ecosystem occurred abruptly and concomitant with the first major Antarctic glaciation in the earliest Oligocene (~33.6 million years ago). This turnover marks a regime shift in zooplankton-phytoplankton interactions and community structure, which indicates the appearance of eutrophic and seasonally productive environments on the Antarctic margin. We conclude that earliest Oligocene cooling, ice-sheet expansion, and subsequent sea-ice formation were important drivers of biotic evolution in the Southern Ocean. PMID:23599491

  8. Stable isotopes and Antarctic moss banks: Plants and soil microbes respond to recent warming on the Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Royles, Jessica; Amesbury, Matthew; Ogée, Jérôme; Wingate, Lisa; Convey, Peter; Hodgson, Dominic; Griffiths, Howard; Leng, Melanie; Charman, Dan

    2014-05-01

    The Antarctic Peninsula is one of the most rapidly warming regions on Earth, with air temperature increases of as much as 3°C recorded since the 1950s. However, the longer-term context of this change is limited and existing records, largely relying on ice core data, are not suitably located to be able to trace the spatial signature of change over time. We are working on a project exploiting stable isotope records preserved in moss peat banks spanning 10 degrees of latitude along the Antarctic Peninsula as an archive of late Holocene climate variability. Here we present a unique time series of past moss growth and soil microbial activity that has been produced from a 150 year old moss bank at Lazarev Bay, Alexander Island (69°S), a site at the southern limit of significant plant growth in the Antarctic Peninsula region. These moss banks are ideal archives for palaeoclimate research as they are well-preserved by freezing, generally monospecific, easily dated by radiocarbon techniques, and have sufficiently high accumulation rates to permit decadal resolution. We use accumulation rates, cellulose δ13C and fossil testate amoebae to show that growth rates, assimilation and microbial productivity rose rapidly in the 1960s, consistent with temperature change, although recently may have stalled, concurrent with other evidence. The increase in biological activity is unprecedented in the last 150 years. Along with work completed on Signy Island (60°S), in the South Orkney Islands, in which we used carbon isotope evidence to show recent climate-related enhancement of CO2 assimilation and peat accumulation rates in Antarctica, the observed relationships between moss growth, microbial activity and climate suggests that moss bank records have the potential to test the regional expression of temperature variability shown by instrumental data on the Antarctic Peninsula over centennial to millennial timescales, by providing long-term records of summer growth conditions

  9. Millennial-scale Variability in Antarctic Ice-Sheet Discharge Throughout the Last Deglaciation From Scotia Sea Records of Iceberg-Rafted Debris

    NASA Astrophysics Data System (ADS)

    Clark, P. U.; Weber, M. E.; Timmermann, A.; Lohmann, G.; Menviel, L.; Gladstone, R. M.

    2014-12-01

    The deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (LGM; 26,000 - 19,000 years ago) is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences. This sparseness limits our understanding of the dominant feedbacks between the AIS, Southern Hemisphere climate, and global sea level. Marine records of iceberg-rafted debris (IBRD) provide a nearly continuous signal of ice-sheet dynamics and variability. IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets, but comparable records from the Southern Ocean of the AIS are lacking due to the low resolution and large dating uncertainties in existing sediment cores. Here we present two well-dated, high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation. We document eight events of increased iceberg flux from various parts of the AIS between 19,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after Meltwater Pulse 1A (MWP-1A) and continuing into the late Holocene. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to MWP-1A. Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water, subsurface warming and AIS melt, suggesting that small perturbations to the ice sheet can be substantially enhanced and providing a possible mechanism for rapid sea-level rise.

  10. An analysis of pterosaurian biogeography: implications for the evolutionary history and fossil record quality of the first flying vertebrates

    PubMed Central

    Upchurch, Paul; Andres, Brian; Butler, Richard J.; Barrett, Paul M.

    2015-01-01

    The biogeographical history of pterosaurs has received very little treatment. Here, we present the first quantitative analysis of pterosaurian biogeography based on an event-based parsimony method (Treefitter). This approach was applied to a phylogenetic tree comprising the relationships of 108 in-group pterosaurian taxa, spanning the full range of this clade's stratigraphical and geographical extent. The results indicate that there is no support for the impact of vicariance or coherent dispersal on pterosaurian distributions. However, this group does display greatly elevated levels of sympatry. Although sampling biases and taxonomic problems might have artificially elevated the occurrence of sympatry, we argue that our results probably reflect a genuine biogeographical signal. We propose a novel model to explain pterosaurian distributions: pterosaurs underwent a series of ‘sweep-stakes’ dispersal events (across oceanic barriers in most cases), resulting in the founding of sympatric clusters of taxa. Examination of the spatiotemporal distributions of pterosaurian occurrences indicates that their fossil record is extremely patchy. Thus, while there is likely to be genuine information on pterosaurian diversity and biogeographical patterns in the current data-set, caution is required in its interpretation. PMID:26339122