Getting to the root of mammal origins; novel insights into the evolution of mammalian metabolism from fossil teeth

We propose a sub-micron resolution X-ray computed tomography study of the fossil teeth and jaws of brasilodontid fossils from the Late Triassic of Brazil. Brasilodontids are the sister group to mammaliaforms (basal mammals) and inform on the evolution of traits that define mammals: endothermy (warm bloodedness), determinate growth (growth ceases after sexual maturity) and diphyodonty (only two sets of teeth). We will image growth structures in the teeth and jaws of brasilodontids to estimate their lifespan and growth patterns, as well as tooth replacement rates and patterns. These values will allow us to (1), estimate basal metabolic rate (BMR), post-natal growth rate and growth pattern in brasilodontids for the first time, critical to the debate on the evolution of endothermy; and (2) quantify dental replacement rates, crucial to understanding the acquisition of diphyodonty in mammaliaforms. This will provide vital data on the early evolution of key mammalian characters.