Despite considerable advances in knowledge of the anatomy, ecology and evolution of early mammals, far less is known about their physiology. Evidence is contradictory concerning the timing and fossil groups in which mammalian endothermy arose. To determine the state of metabolic evolution in two of the earliest stem-mammals, the Early Jurassic Morganucodon and Kuehneotherium, we use separate proxies for basal and maximum metabolic rate. Here we report, using synchrotron X-ray tomographic imaging of incremental tooth cementum, that they had maximum lifespans considerably longer than comparably sized living mammals, but similar to those of reptiles, and so they likely had reptilian-level basal metabolic rates. Measurements of femoral nutrient foramina show Morganucodon had blood flow rates intermediate between living mammals and reptiles, suggesting maximum metabolic rates increased evolutionarily before basal metabolic rates. Stem mammals lacked the elevated endothermic metabolism of living mammals, highlighting the mosaic nature of mammalian physiological evolution.

2006) Current status of species-level representation in faunas from selected fossil localities in the Riversleigh World Heritage Area,

The Pig-footed Bandicoot, Chaeropus ecaudatus, an extinct arid-adapted bandicoot, was named in 1838 based on a specimen without a tail from the Murray River in New South Wales. Two additional species were later named, C. castanotis and C. occidentalis, which have since been synonymised with C. ecaudatus. Taxonomic research on the genus is rather difficult because of the limited material available for study. Aside from the types of C. castanotis and C. occidentalis housed at the Natural History Museum in London, and the type of C. ecaudatus at the Australian Museum in Sydney, there are fewer than 30 other modern specimens in other collections scattered around the world. Examining skeletal and dental characters for several specimens, and using a combination of traditional morphology, morphometrics, palaeontology and molecular phylogenetics, we have identified two distinct species, C. ecaudatus and C. yirratji sp. nov., with C. ecaudatus having two distinct subspecies, C. e. ecaudatus and C. e. occidentalis. We use palaeontological data to reconstruct the pre-European distribution of the two species, and review the ecological information known about these extinct taxa.

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