Life histories of Mesozoic polar mammals and the evolution of mammalian traits

We propose sub-micron resolution X-ray computed tomography of growth structures in the teeth and jaws of Mesozoic mammal fossils to establish the evolution of mammalian traits: elevated basal metabolic rate (BMR) and growth rate, and one phase of tooth replacement (diphyodonty). We will study fossil mammals from southern Australia including the earliest monotreme, and the globally distributed mammaliaform fossil Morganucodon. During the Cretaceous southern Australia sat within the Antarctic circle experiencing months of darkness and standing ice. We will test if the life histories (lifespan, BMR, growth rate, tooth replacement rate and pattern) of these unique polar mammals were significantly different to a) extant mammals, b) earlier stem mammals such as Morganucodon (with lower metabolic rates but diphyodont dentition). This study will provide valuable insight into the life histories of the earliest polar mammals and the macroevolution of mammalian physiology.