Oxygen isotopes suggest elevated thermometabolism within multiple Permo-Triassic therapsid clades
Résumé
Nowadays, birds and mammals are the only true endothermic homeothermic animals. They produce and regulate their internal temperature quite independently from ambient environmental temperatures. Whereas birds likely inherited their thermophysiology from their dinosaur ancestors, the oldest definitive evidence of mammal endothermy dates back to the Middle Jurassic. However, anatomical clues suggest an older origin, during the Triassic or the Permian. We analysed apatite stable oxygen isotope compositions of a representative sample of Permo-Triassic therapsids to investigate the origin and timing of mammal thermoregulation. All main clades of Eutherapsida were sampled (Dinocephalia, Anomodontia, Gorgonopsia, Therocephalia and Cynodontia). By comparing the d18Op values of therapsid bone and tooth apatites with those of coexisting tetrapods of various ecologies and physiologies (terrestrial and semi-aquatic parareptiles, semi-aquatic stereospondyl and terrestrial archosauriforms), thermoregulatory strategies estimated from body temperature differences are proposed. Our results indicate that amongst the Dicynodontia, Induan Lystrosauridae and Anisian and Camian Kannemeyeriiformes may have acquired elevated thermometabolism. A similar result has been obtained in the Cynodontia clade within Anisian Cynognathia and Rhaetian Mammaliaformes. Our results indicate that mammalian thermoregulation possibly originated from the Epicynodontia group during the middle late Permian. It appears that the timing of acquisition of elevated thermometabolism in amniotes coincides with major global climatic and environmental fluctuations that may have acted as a selective pressure during the origin of mammal endothermy.
Domaines
| Origine | Fichiers produits par l'(les) auteur(s) |
|---|---|
| Licence |