Evidence for a Reptile-like physiology in Early Jurassic stem-Mammals
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Recent discoveries and analyses have revolutionised our knowledge of Mesozoic Mammals, revealing novel aspects of their ecology, development, systematics, and macroevolution. However, details of physiology are more difficult to determine from fossils, and our knowledge of physiological evolution remains comparatively poor. Living Mammals are endotherms, possessing the ability to control and maintain metabolically produced heat and have a substantially higher capacity for sustained aerobic activity than ectothermic Animals. The origin of endothermy is an important event in Mammalian evolution, often noted as key to their success. There are a number of competing evolutionary hypotheses for the origin of endothermy: (a) selection for higher maximum metabolic rates enhanced sustained aerobic activity, selection for higher basal metabolic rates enhanced thermoregulatory control, or maximum metabolic rates and basal metabolic rates evolved in lockstep with each other.