Post‐Permian Radiation

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Abstract Events at the close of the Permian Period, led to the most severe mass extinction of the Phanerozoic. Sepkoski's ‘Palaeozoic Fauna’ suffered most; the surviving groups, more ‘modern’ in aspect, were those that would seed the post‐Permian radiation. This radiation has long been identified as a ‘delayed’ radiation, being apparently of longer duration than other post‐extinction radiations, although recent advances in radiometric dating have shortened the Early Triassic. Comparing rates of recovery between different groups or regions is not straightforward because the quality of the fossil record is rather poor during the Early Triassic. The analysis of trace fossils provides one approach to assessing ecological recovery in the absence of well‐preserved shells. Groups that radiated into vacant or largely vacated ecospace include the bivalves, which colonised deeper infaunal habitats; the Scleractinia which replaced the Palaeozoic reef‐building metazoans; and the reptiles that became top marine predators. Key Concepts: The Late Permian mass extinction event is the most severe extinction event known from the fossil record. Late Permian global warming led to a reduction in ocean circulation, increased ocean stratification and expansion of low‐oxygen ‘dead zones’. The Palaeozoic fauna is dominated by sessile, epifaunal filter‐feeders such as corals, crinoids and brachiopods, whereas the Modern fauna is dominated by motile, epifaunal and infaunal organisms such as bivalves, echinoids and gastropods. The best‐preserved fossil remains usually require an absence of scavenging animals, rapid burial and rapid mineralisation. The quality of the fossil record is not constant through time and is affected by a number of different sampling and preservational factors. Trace fossils provide evidence of the activities of benthic organisms that may not be preserved as body fossils, and are the only records of the responses of these animals to past extinction events.