Abstract
During the end-Permian mass extinction, marine ecosystems suffered a major drop in diversity, which was maintained throughout the Early Triassic until delayed recovery during the Middle Triassic. This depressed diversity in the Early Triassic correlates with multiple major perturbations to the global carbon cycle, interpreted as either intrinsic ecosystem or external palaeoenvironmental effects. In contrast, the terrestrial record of extinction and recovery is less clear; the effects and magnitude of the end-Permian extinction on non-marine vertebrates are particularly controversial. We use specimen-level data from southern Africa and Russia to investigate the palaeodiversity dynamics of non-marine tetrapods across the Permo-Triassic boundary by analysing sample-standardized generic richness, evenness and relative abundance. In addition, we investigate the potential effects of sampling, geological and taxonomic biases on these data. Our analyses demonstrate that non-marine tetrapods were severely affected by the end-Permian mass extinction, and that these assemblages did not begin to recover until the Middle Triassic. These data are congruent with those from land plants and marine invertebrates. Furthermore, they are consistent with the idea that unstable low-diversity post-extinction ecosystems were subject to boom–bust cycles, reflected in multiple Early Triassic perturbations of the carbon cycle.
Highlights
The end-Permian mass extinction event at approximately 252.6 millions of years ago (Ma) [1] is the largest mass extinction in Phanaerozoic Earth history in terms of diversity loss [2,3]
Southern African dataset was rarefied to 241 specimens and the Russia dataset to 48 specimens; these levels were chosen based on the smallest sample size among the temporal bins
Despite sample sizes that range from less than 250 specimens to greater than 2500 specimens, the rarefaction curves show a clear difference in generic richness among southern African Permo-Triassic Assemblage Zone (AZ)
Summary
The end-Permian mass extinction event at approximately 252.6 Ma [1] is the largest mass extinction in Phanaerozoic Earth history in terms of diversity loss [2,3]. Detailed examination of the marine fossil record demonstrates that these ecosystems took 5 –8 million years to recover; not until the early Middle Triassic (Anisian) are diversity and complexity comparable with that of pre-extinction faunas [6 – 8] The cause of this mass extinction has not been fully resolved, but multiple lines of evidence point to greenhouse gases and other compounds from the Siberian Traps [1,6,9,10] as a trigger. METHODS (a) Choice of datasets To investigate non-marine vertebrate palaeoecology across the Permo-Triassic boundary, we chose two published regional specimen-level datasets identified to genus These data are ideal because they allow for easy sample-size standardization (i.e. by number of specimens), lessen problems with longdistance stratigraphic correlation and allow identification of any regional differences in patterns (in contrast with global analyses).
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