Abstract
Extinction selectivity determines the direction of macroevolution, especially during mass extinction; however, its driving mechanisms remain poorly understood. By investigating the physiological selectivity of marine animals during the Permian-Triassic mass extinction, we found that marine clades with lower O(2)-carrying capacity hemerythrin proteins and those relying on O(2) diffusion experienced significantly greater extinction intensity and body-size reduction than those with higher O(2)-carrying capacity hemoglobin or hemocyanin proteins. Our findings suggest that animals with high O(2)-carrying capacity obtained the necessary O(2) even under hypoxia and compensated for the increased energy requirements caused by ocean acidification, which enabled their survival during the Permian-Triassic mass extinction. Thus, high O(2)-carrying capacity may have been crucial for the transition from the Paleozoic to the Modern Evolutionary Fauna.