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      Climate constrains the evolutionary history and biodiversity of crocodylians

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          Summary

          Crocodylians and their relatives have a rich evolutionary history. Here we show long-term decline of terrestrial crocodylians driven by decreasing temperatures but no relationship between temperature and biodiversity for marine crocodylians over their 250 million year history.

          Abstract

          The fossil record of crocodylians and their relatives (pseudosuchians) reveals a rich evolutionary history, prompting questions about causes of long-term decline to their present-day low biodiversity. We analyse climatic drivers of subsampled pseudosuchian biodiversity over their 250 million year history, using a comprehensive new data set. Biodiversity and environmental changes correlate strongly, with long-term decline of terrestrial taxa driven by decreasing temperatures in northern temperate regions, and biodiversity decreases at lower latitudes matching patterns of increasing aridification. However, there is no relationship between temperature and biodiversity for marine pseudosuchians, with sea-level change and post-extinction opportunism demonstrated to be more important drivers. A ‘modern-type' latitudinal biodiversity gradient might have existed throughout pseudosuchian history, and range expansion towards the poles occurred during warm intervals. Although their fossil record suggests that current global warming might promote long-term increases in crocodylian biodiversity and geographic range, the 'balancing forces' of anthropogenic environmental degradation complicate future predictions.

          Abstract

          Crocodylians and their relatives have a rich evolutionary history. Here the authors show long-term decline of terrestrial crocodylians driven by decreasing temperatures but no relationship between temperature and biodiversity for marine crocodylians over their 250 million year history.

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          Most cited references20

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          The Phanerozoic record of global sea-level change.

          K. Miller (2005)
          We review Phanerozoic sea-level changes [543 million years ago (Ma) to the present] on various time scales and present a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 +/- 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 10(4)- to 10(6)-year scale, but a link between oxygen isotope and sea level on the 10(7)-year scale must be due to temperature changes that we attribute to tectonically controlled carbon dioxide variations. Sea-level change has influenced phytoplankton evolution, ocean chemistry, and the loci of carbonate, organic carbon, and siliciclastic sediment burial. Over the past 100 My, sea-level changes reflect global climate evolution from a time of ephemeral Antarctic ice sheets (100 to 33 Ma), through a time of large ice sheets primarily in Antarctica (33 to 2.5 Ma), to a world with large Antarctic and large, variable Northern Hemisphere ice sheets (2.5 Ma to the present).
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            Effects of sampling standardization on estimates of Phanerozoic marine diversification.

            Global diversity curves reflect more than just the number of taxa that have existed through time: they also mirror variation in the nature of the fossil record and the way the record is reported. These sampling effects are best quantified by assembling and analyzing large numbers of locality-specific biotic inventories. Here, we introduce a new database of this kind for the Phanerozoic fossil record of marine invertebrates. We apply four substantially distinct analytical methods that estimate taxonomic diversity by quantifying and correcting for variation through time in the number and nature of inventories. Variation introduced by the use of two dramatically different counting protocols also is explored. We present sampling-standardized diversity estimates for two long intervals that sum to 300 Myr (Middle Ordovician-Carboniferous; Late Jurassic-Paleogene). Our new curves differ considerably from traditional, synoptic curves. For example, some of them imply unexpectedly low late Cretaceous and early Tertiary diversity levels. However, such factors as the current emphasis in the database on North America and Europe still obscure our view of the global history of marine biodiversity. These limitations will be addressed as the database and methods are refined.
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              The shifting balance of diversity among major marine animal groups.

              J Alroy (2010)
              The fossil record demonstrates that each major taxonomic group has a consistent net rate of diversification and a limit to its species richness. It has been thought that long-term changes in the dominance of major taxonomic groups can be predicted from these characteristics. However, new analyses show that diversity limits may rise or fall in response to adaptive radiations or extinctions. These changes are idiosyncratic and occur at different times in each taxa. For example, the end-Permian mass extinction permanently reduced the diversity of important, previously dominant groups such as brachiopods and crinoids. The current global crisis may therefore permanently alter the biosphere's taxonomic composition by changing the rules of evolution.
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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Pub. Group
                2041-1723
                24 September 2015
                2015
                : 6
                : 8438
                Affiliations
                [1 ]Department of Earth Science and Engineering, Imperial College London , London SW7 2AZ, UK
                [2 ]Department of Earth Sciences, University of Oxford , Oxford OX1 3AN, UK
                [3 ]Department of Paleobiology, National Museum of Natural History , Smithsonian Institution, PO Box 37012, Washington DC 20013-7012, USA
                [4 ]School of Geography, Earth and Environmental Sciences, University of Birmingham , Birmingham B15 2TT, UK
                Author notes
                [*]

                These authors contributed equally to this work.

                Article
                ncomms9438
                10.1038/ncomms9438
                4598718
                26399170
                87fc0afa-0b8f-4d87-894e-47d85297110c
                Copyright © 2015, Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 03 June 2015
                : 20 August 2015
                Categories
                Article

                General geosciences,Ecology,Paleontology,Animal science & Zoology
                Crocodylians,Climate Change
                General geosciences, Ecology, Paleontology, Animal science & Zoology
                Crocodylians, Climate Change

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