COMPARATIVE PHYSIOLOGICAL SELECTIVITY OF PENNSYLVANIAN TO JURASSIC EXTINCTION IN BONY FISH, SHARKS AND INVERTEBRATES

The end-Permian and end-Triassic extinctions coincided with flood basalt eruptions that would have released large quantities of CO₂ into the atmosphere, leading to ocean warming, anoxia, and perhaps acidification. Multiple stresses present during these extinction events provide analogues for anthropogenic CO₂ emissions and can help us understand which taxonomic groups will be threatened by ocean acidification and warming. Fish have cellular mechanisms to buffer extracellular pH changes from exercise-induced metabolic CO₂ production, which also prove advantageous in buffering against changes in seawater pH. However, active swimming fish have higher respiratory and metabolic demands and might be more susceptible to the stresses of anoxia than less active taxa. Assessing the extinction of fish during CO₂-driven extinctions will test the hypothesis that active fish are less vulnerable than sessile marine invertebrates. We compiled a database of fossil fish occurrences from the Pennsylvanian to the Middle Jurassic, using the Paleobiology Database, to quantify fish extinction rates during background and mass extinctions. We used maximum likelihood estimation to compare models using separate extinction rates for vertebrates and invertebrates to models with one extinction rate for all groups. Our results show that sharks suffered less extinction than marine invertebrates during the end-Permian crisis. During the end-Triassic extinction, both sharks and bony fish suffered extinction comparable to that of marine invertebrates. These results may reflect changes in physiological adaptation of sharks or different environmental stresses of the end-Permian and end-Triassic extinctions.