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      Cascading trend of Early Paleozoic marine radiations paused by Late Ordovician extinctions

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          Significance

          The first 120 million years of Phanerozoic life witnessed significant changes in biodiversity levels. Attempts to correlate these changes to potential short-term environmental drivers have been hampered by the crude temporal resolution of current biodiversity estimates. We present a biodiversity curve for the Early Paleozoic with high temporal precision. It shows that once equatorial sea-surface temperatures fell to present-day levels during the early Mid Ordovician, marine biodiversity accumulation accelerated dramatically. However, this acceleration ceased as increased volcanism commenced during the mid-Late Ordovician. Since biodiversity levels were not restored for at least ∼35 million years, this finding redefines the nature of the end Ordovician mass extinctions and further reframes the Silurian as a prolonged recovery interval.

          Abstract

          The greatest relative changes in marine biodiversity accumulation occurred during the Early Paleozoic. The precision of temporal constraints on these changes is crude, hampering our understanding of their timing, duration, and links to causal mechanisms. We match fossil occurrence data to their lithostratigraphical ranges in the Paleobiology Database and correlate this inferred taxon range to a constructed set of biostratigraphically defined high-resolution time slices. In addition, we apply capture–recapture modeling approaches to calculate a biodiversity curve that also considers taphonomy and sampling biases with four times better resolution of previous estimates. Our method reveals a stepwise biodiversity increase with distinct Cambrian and Ordovician radiation events that are clearly separated by a 50-million-year-long period of slow biodiversity accumulation. The Ordovician Radiation is confined to a 15-million-year phase after which the Late Ordovician extinctions lowered generic richness and further delayed a biodiversity rebound by at least 35 million years. Based on a first-differences approach on potential abiotic drivers controlling richness, we find an overall correlation with oxygen levels, with temperature also exhibiting a coordinated trend once equatorial sea surface temperatures fell to present-day levels during the Middle Ordovician Darriwilian Age. Contrary to the traditional view of the Late Ordovician extinctions, our study suggests a protracted crisis interval linked to intense volcanism during the middle Late Ordovician Katian Age. As richness levels did not return to prior levels during the Silurian—a time of continental amalgamation—we further argue that plate tectonics exerted an overarching control on biodiversity accumulation.

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          Approaching a state shift in Earth's biosphere.

          Localized ecological systems are known to shift abruptly and irreversibly from one state to another when they are forced across critical thresholds. Here we review evidence that the global ecosystem as a whole can react in the same way and is approaching a planetary-scale critical transition as a result of human influence. The plausibility of a planetary-scale 'tipping point' highlights the need to improve biological forecasting by detecting early warning signs of critical transitions on global as well as local scales, and by detecting feedbacks that promote such transitions. It is also necessary to address root causes of how humans are forcing biological changes.
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            Phanerozoic trends in the global diversity of marine invertebrates.

            It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.
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              A General Methodology for the Analysis of Capture-Recapture Experiments in Open Populations

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                Author and article information

                Journal
                Proc Natl Acad Sci U S A
                Proc. Natl. Acad. Sci. U.S.A
                pnas
                pnas
                PNAS
                Proceedings of the National Academy of Sciences of the United States of America
                National Academy of Sciences
                0027-8424
                1091-6490
                9 April 2019
                25 March 2019
                25 March 2019
                : 116
                : 15
                : 7207-7213
                Affiliations
                [1] aNatural History Museum of Denmark, University of Copenhagen , DK-1350 Copenhagen, Denmark;
                [2] bFinnish Museum of Natural History, University of Helsinki , 00014 Helsinki, Finland;
                [3] cSchool of Earth Sciences, University of Bristol , Bristol BS8 1RL, United Kingdom
                Author notes
                1To whom correspondence should be addressed. Email: christian@ 123456snm.ku.dk .

                Edited by Lauren Sallan, University of Pennsylvania, Philadelphia, PA, and accepted by Editorial Board Member Neil H. Shubin February 27, 2019 (received for review December 13, 2018)

                Author contributions: C.M.Ø.R. and B.K. designed research; C.M.Ø.R., B.K., M.L.N., and J.C. performed research; C.M.Ø.R. and B.K. analyzed data; and C.M.Ø.R. and B.K. wrote the paper.

                Article
                201821123
                10.1073/pnas.1821123116
                6462056
                30910963
                c57859c6-5cfd-475a-8877-aed33b8680c4
                Copyright © 2019 the Author(s). Published by PNAS.

                This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

                Page count
                Pages: 7
                Product
                Funding
                Funded by: Villum Fonden (Villum Foundation) 100008398
                Award ID: VKR023452
                Award Recipient : Christian Mac Ørum Rasmussen
                Funded by: Geocenter Danmark (Geocenter Denmark) 100011044
                Award ID: 2015-5
                Award Recipient : Christian Mac Ørum Rasmussen
                Funded by: Geocenter Danmark (Geocenter Denmark) 100011044
                Award ID: 3-2017
                Award Recipient : Christian Mac Ørum Rasmussen
                Categories
                PNAS Plus
                Physical Sciences
                Earth, Atmospheric, and Planetary Sciences
                From the Cover
                PNAS Plus

                earth state shifts,biodiversity accumulation,ordovician radiation,capture–recapture,first differences

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