TY - JOUR T1 - Reptile-like physiology in Early Jurassic stem-mammals JF - bioRxiv DO - 10.1101/785360 SP - 785360 AU - Elis Newham AU - Pamela G. Gill AU - Philippa Brewer AU - Michael J. Benton AU - Vincent Fernandez AU - Neil J. Gostling AU - David Haberthür AU - Jukka Jernvall AU - Tuomas Kankanpää AU - Aki Kallonen AU - Charles Navarro AU - Alexandra Pacureanu AU - Berit Zeller-Plumhoff AU - Kelly Richards AU - Kate Robson-Brown AU - Philipp Schneider AU - Heikki Suhonen AU - Paul Tafforeau AU - Katherine Williams AU - Ian J. Corfe Y1 - 2019/01/01 UR - http://biorxiv.org/content/early/2019/10/10/785360.abstract N2 - 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. ER -