Endothermic physiology of extinct megatooth sharks
Significance
Otodus megalodon was a gigantic shark that went extinct around 3.6 Mya. It could grow to the enormous size of at least 15 m long, making it one of the largest apex marine predators since the Mesozoic. Here, we test hypotheses relating to its extinction by providing quantitative estimates of its body temperature, thereby constraining its thermal physiology. We found that O. megalodon had body temperatures significantly elevated compared to other sharks, consistent with it having a degree of internal heat production as modern warm-blooded (endothermic) animals do. High metabolic costs associated with having at least partial endothermy may have contributed to its vulnerability to extinction compared to other shark species that persist until this day.
Abstract
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.
| 2023 | PNAS