Endothermic physiology of extinct megatooth sharks.
灭绝巨齿鲨类的内温生理机制

Authors / 作者: Griffiths ML, Eagle RA, Kim SL, Flores RJ, Becker MA, Maisch HM, Trayler RB, Chan RL, McCormack J, Akhtar AA, Tripati AK, Shimada K.
Journal / 期刊: Proceedings of the National Academy of Sciences of the United States of America
Year / 年份: 2023
DOI: 10.1073/pnas.2218153120
Publisher / 出版社: https://www.pnas.org/doi/10.1073/pnas.2218153120
Abstract source / 摘要来源: https://europepmc.org/article/MED/37364100

Author abstract / 作者原文摘要
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.

Summary basis / 解读依据
摘要解读依据已查看的索引作者摘要；如已保存全文，可用于进一步阅读。
Summary based on the inspected indexed author abstract; archived full text, when available, is provided for further reading.

Key findings / 主要发现
团簇同位素测温与磷酸盐氧同位素显示，巨齿鲨体温高于周围海水及共存鲨鱼，为此前生物物理模型提出的体温调节能力提供地球化学支持。
Clumped-isotope thermometry and phosphate oxygen isotopes indicate that megalodon maintained a warmer body temperature than surrounding water and coexisting sharks. The results provide geochemical support for thermoregulation previously inferred through biophysical modeling.

Conclusions / 结论
内温性可能促进巨大体型，同时带来较高代谢成本。作者认为这些成本也可能增加灭绝脆弱性，但这一因果解释仍属于推断。
Endothermy may have supported gigantism but imposed high metabolic costs. The authors suggest these costs could also have increased extinction vulnerability; that causal explanation remains an interpretation.

Relevance / 关联说明
直接研究清单物种，或研究广义类群中的代表物种。
Direct research on the listed species or a representative of the broadly named group.