Permian– T riassic O steichthyes (bony fishes): diversity dynamics and body size evolution

The P ermian and T riassic were key time intervals in the history of life on E arth. Both periods are marked by a series of biotic crises including the most catastrophic of such events, the end‐ P ermian mass extinction, which eventually led to a major turnover from typical P alaeozoic faunas and floras to those that are emblematic for the M esozoic and C enozoic. Here we review patterns in P ermian– T riassic bony fishes, a group whose evolutionary dynamics are understudied. Based on data from primary literature, we analyse changes in their taxonomic diversity and body size (as a proxy for trophic position) and explore their response to P ermian– T riassic events. Diversity and body size are investigated separately for different groups of O steichthyes ( D ipnoi, A ctinistia, ‘ P alaeopterygii’, ‘ S ubholostei’, H olostei, T eleosteomorpha), within the marine and freshwater realms and on a global scale (total diversity) as well as across palaeolatitudinal belts. Diversity is also measured for different palaeogeographical provinces. Our results suggest a general trend from low osteichthyan diversity in the P ermian to higher levels in the T riassic. Diversity dynamics in the P ermian are marked by a decline in freshwater taxa during the C isuralian. An extinction event during the end‐ G uadalupian crisis is not evident from our data, but ‘palaeopterygians’ experienced a significant body size increase across the G uadalupian– L opingian boundary and these fishes upheld their position as large, top predators from the L ate P ermian to the L ate T riassic. Elevated turnover rates are documented at the P ermian– T riassic boundary, and two distinct diversification events are noted in the wake of this biotic crisis, a first one during the E arly T riassic (dipnoans, actinistians, ‘palaeopterygians’, ‘subholosteans’) and a second one during the M iddle T riassic (‘subholosteans’, neopterygians). The origination of new, small taxa predominantly among these groups during the M iddle T riassic event caused a significant reduction in osteichthyan body size. Neopterygii, the clade that encompasses the vast majority of extant fishes, underwent another diversification phase in the L ate T riassic. The T riassic radiation of O steichthyes, predominantly of A ctinopterygii, which only occurred after severe extinctions among C hondrichthyes during the M iddle– L ate P ermian, resulted in a profound change within global fish communities, from chondrichthyan‐rich faunas of the P ermo‐ C arboniferous to typical M esozoic and C enozoic associations dominated by actinopterygians. This turnover was not sudden but followed a stepwise pattern, with leaps during extinction events.