ECOLOGICAL TOLERANCE OF END-PERMIAN MASS EXTINCTION SURVIVORS

Delayed recovery following the end-Permian extinction crisis is the longest documented recovery interval associated with any of the ‘Big 5’ mass extinctions. Initial catastrophic environmental change, followed by intervals of repeated climactic instability associated with ongoing Siberian Traps volcanic pulses, is thought to have favored the survival and proliferation of generalist taxa, as exemplified by the ecological dominance of the Early Triassic ‘disaster taxa’. This study aims to quantify the ecological tolerance of Permian-Triassic benthic marine invertebrate taxa by exploring their degree of substrate affinity as a measure of ecological generalism. Affinity for specific substrate lithologies was calculated with the standardized relative affinity (SRA) metric using a global dataset of marine benthic invertebrates from the Paleobiology Database. Genera that showed strong affinity for either carbonate and siliciclastic lithologies were regarded as ecological specialists while genera that showed weak or no affinity were regarded as generalists. Generally, Permian extinction victims tend to exhibit stronger substrate preferences, while Permian survivors exhibit weaker affinities. Permian taxa with the most extreme affinities are preferentially culled during the extinction event, leaving a surviving Triassic fauna that exhibit decreased SRA variance and a higher degree of generalism. Additionally, median SRA values in extinction survivors in rhynchonellid brachiopods, bivalves, and gastropods trend towards more generalist values as compared to extinction victims. Interestingly, novel Triassic genera that originated after the extinction event tend to have decreased variance in substrate preferences as well, and appear to be even more generalist in their substrate affinities than even Permian survivors. This suggests that, despite amelioration of conditions after the Early Triassic recovery interval, the relatively extreme substrate specialization observed in Permian extinction victims is not re-established by the Triassic. Ongoing efforts to comprehensively characterize ecological restructuring following the end-Permian mass extinction reveal ever more nuanced patterns of complex and dynamic recovery in marine benthic ecosystems.