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. Bony fish and sharks (Actinoptyergii and Chondrichthyes) 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. 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 and shark occurrences from the Pennsylvanian to the Middle Jurassic, using the Paleobiology Database, to quantify 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. We also reviewed photographs of shark teeth from primary sources in order to classify them based on morphology and interpret changes in feeding mode and activity level through the interval of study. 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. Our results show that sharks and fish are adaptable groups that may have survived extinction through their adaptations for an active life habit, and may be more likely than marine invertebrates to survive extinction in modern global change scenarios.