Reptile-like physiology in Early Jurassic stem-mammals

Abstract There is uncertainty regarding the timing and fossil species in which mammalian endothermy arose, with few studies of stem-mammals on key aspects of endothermy such as basal or maximum metabolic rates, or placing them in the context of living vertebrate metabolic ranges. Synchrotron X-ray i...

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Published inbioRxiv
Main Authors Newham, Elis, Gill, Pamela G, Brewer, Philippa, Benton, Michael J, Fernandez, Vincent, Gostling, Neil J, Haberthür, David, Jernvall, Jukka, Kankanpää, Tuomas, Kallonen, Aki, Navarro, Charles, Pacureanu, Alexandra, Zeller-Plumhoff, Berit, Richards, Kelly, Robson-Brown, Kate, Schneider, Philipp, Suhonen, Heikki, Tafforeau, Paul, Williams, Katherine, Corfe, Ian J
Format Paper
LanguageEnglish
Published Cold Spring Harbor Cold Spring Harbor Laboratory Press 10.10.2019
Subjects
Blood flow
Cementum
Femur
Fossils
Metabolic rate
Metabolism
Reptiles & amphibians
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Summary:Abstract There is uncertainty regarding the timing and fossil species in which mammalian endothermy arose, with few studies of stem-mammals on key aspects of endothermy such as basal or maximum metabolic rates, or placing them in the context of living vertebrate metabolic ranges. Synchrotron X-ray imaging of incremental tooth cementum shows two Early Jurassic stem-mammals, Morganucodon and Kuehneotherium, had lifespans (a basal metabolic rate proxy) considerably longer than comparably sized living mammals, but similar to reptiles. Morganucodon also had femoral blood flow rates (a maximum metabolic rate proxy) intermediate between living mammals and reptiles. This shows maximum metabolic rates increased evolutionarily before basal rates, and that contrary to previous suggestions of a Triassic origin, Early Jurassic stem-mammals lacked the endothermic metabolism of living mammals. One Sentence Summary Surprisingly long lifespans and low femoral blood flow suggest reptile-like physiology in key Early Jurassic stem-mammals. Footnotes * ↵* e-mail: pam.gill{at}bristol.ac.uk; ian.corfe{at}helsinki.fi * The abstract and acknowledgements of the manuscript have had minor alterations.
DOI:10.1101/785360