Endothermic physiology of extinct megatooth sharks

The evolution of the extinct megatooth shark, Otodus megalodon, and its close phylogenetic relatives remains enigmatic. A central question persists regarding the thermophysiological origins of these large predatory sharks through geologic time, including whether O. megalodon was ectothermic or endothermic (including regional endothermy), and whether its thermophysiology could help to explain the iconic shark's gigantism and eventual demise during the Pliocene. To address these uncertainties, we present unique geochemical evidence for thermoregulation in O. megalodon from both clumped isotope paleothermometry and phosphate oxygen isotopes. Our results show that O. megalodon had an overall warmer body temperature compared with its ambient environment and other coexisting shark species, providing quantitative and experimental support for recent biophysical modeling studies that suggest endothermy was one of the key drivers for gigantism in O. megalodon and other lamniform sharks. The gigantic body size with high metabolic costs of having high body temperatures may have contributed to the vulnerability of Otodus species to extinction when compared to other sympatric sharks that survived the Pliocene epoch.

Automated summary

The study provides unique geochemical evidence for thermoregulation in the extinct megatooth shark, Otodus megalodon. The results show that O. megalodon had a warmer body temperature compared to its environment and other shark species, supporting recent biophysical modeling studies that suggest endothermy played a role in its gigantism. The high metabolic costs associated with the large body size and high body temperatures may have contributed to the extinction of Otodus species compared to other sympatric sharks.