Timing and magnitude of tetrapod extinctions across the Permo-Triassic boundary |
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| Institution: | 1. Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Martí Franques s/n, 08028 Barcelona, Spain;2. Geosciences Barcelona, GEO3BCN, CSIC, Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain;3. Departamento de Geología, Universidad de Salamanca, 37008 Salamanca, Spain;4. School of Geography, Geology and the Environment, University of Leicester, Leicester LE1 7RH, UK;1. Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, Berkeley, CA 94720, USA;2. Department of Paleobiology, NMNH Smithsonian Institution, Washington, DC, 20560, USA;3. Department of Physiology and Developmental Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, 75236 Uppsala, Sweden;4. Centre de Recherches en Paléobiodiversité et Paléoenvironnements (UMR 7207 CNRS-MNHN-UPMC), Muséum national d''Histoire naturelle, CP 38, 8 rue Buffon, F-75005 Paris, France;5. Karoo Palaeontology, Iziko: South African Museum, Cape Town 8000, South Africa;6. Evolutionary Studies Institute, University of Witwatersrand, 1 Jan Smuts Avenue, Johannesburg 2000, South Africa;7. Burke Museum and Department of Biology, University of Washington, Seattle, WA 98195, USA;8. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, TX 75275-0395, USA;9. Institut de Recherches en Sciences Humaines, Niamey, Niger |
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| Abstract: | A review of the tetrapod (amphibian and amniote) record across the Permo-Triassic boundary (PTB) indicates a global evolutionary turnover of tetrapods close to the PTB. There is also a within-Guadalupian tetrapod extinction here called the dinocephalian extinction event, probably of global extent. The dinocephalian extinction event is a late Wordian or early Capitanian extinction based on biostratigraphic data and magnetostratigraphy (the extinction precedes the Illawara reversal), so it is not synchronous with the end-Guadalupian marine extinction. The Russian PTB section documents two tetrapod extinction events, one just before the dinocephalian extinction event and the other at the base of the Lystrosaurus assemblage. However, generic diversity across the latter extinction remains essentially the same despite a total evolutionary turnover of tetrapod genera. The Chinese and South African sections document the stratigraphic overlap of Dicynodon and Lystrosaurus. In the Karoo basin, the lowest occurrence of Lystrosaurus is in a stratigraphic interval of reversed magnetic polarity, which indicates it predates the marine-defined PTB, so, as previously suggested by some workers, the lowest occurrence of Lystrosaurus cannot be used to identify the PTB in nonmarine strata. Correlation of the marine PTB section at Meishan, southern China, to the Karoo basin based primarily on magnetostratigraphy indicates that the main marine extinction preceded the PTB tetrapod extinction event. The ecological severity of the PTB tetrapod extinction event has generally been overstated, and the major change in tetrapod assemblages that took place across the PTB was the prolonged and complex “replacement” of therapsids by archosaurs that began before the end of the Permian and was not complete until well into the Triassic. The tetrapod extinctions are not synchronous with the major marine extinctions at the end of the Guadalupian and just before the end of the Permian, so the idea of catastrophic causes of synchronous PTB extinctions on land and sea should be reconsidered. |
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