Permian tetrapod extinction events

Four substantial tetrapod extinctions have been identified during the Permian, but there was only one mass extinction of tetrapods during the Permian, the dinocephalian extinction event near the end of middle Permian time. A re-evaluation of the best record of early Permian tetrapods, from the southwestern USA, does not identify an early Permian mass extinction. There is a hiatus (Olson's gap) in the global record of Permian tetrapods across the early-middle Permian boundary. Across the gap, eupelycosaur-dominated assemblages were replaced by therapsid-dominated assemblages, but the gap in the tetrapod fossil record makes it impossible to establish the magnitude, precise timing and structure of the extinctions that took place across Olson's gap. The only Permian mass extinction of tetrapods is the dinocephalian extinction event, which saw the total extinction of dinocephalians and major diversity drops in gorgonopsians and therocephalians. The changeover from dinocephalian assemblages to assemblages without dinocephalians in various parts of Permian Pangea suggests that the dinocephalian extinction event was a global event. The late Permian tetrapod extinctions are older than the end-Permian marine extinctions. Furthermore, the magnitude of the diversity drop and ecological severity of the end-Permian tetrapod extinctions have been greatly overstated. Analysis of the tetrapod fossil record in the Karoo basin of South Africa indicates a stepwise late Permian tetrapod extinction that took at least 250,000 years and perhaps more than a million years. The culmination of this stepwise extinction is a loss of genera not much above an inferred background extinction rate of Permian tetrapod genera and resembles the amount of turnover seen at several other boundaries of Permian and Triassic land-vertebrate faunachrons. The case for coeval land plant, insect and tetrapod extinctions during the Permian is a weak one. The first coeval marine and nonmarine mass extinctions of the Phanerozoic were likely the end-Guadalupian extinction. Climate change, notably greenhouse climates, may have driven Permian tetrapod extinctions, but that hypothesized relationship needs better documentation.199