The evolution of mammalian body temperature: the Cenozoic supraendothermic pulses
In this study, I investigated the source(s) of variation in the body temperatures of mammals. I also attempted to reconstruct ancestral normothermic rest-phase body temperature states using a maximum parsimony approach. Body temperature at the familial level is not correlated with body mass. For small mammals, except the Macroscelidae, previously identified correlates, such as climate adaptation and zoogeography explained some, but not all, Tb apomorphies. At the species level in large cursorial mammals, there was a significant correlation between body temperature and the ratio between metatarsal length and femur length, the proxy for stride length and cursoriality. With the exception of two primate families, all supraendothermic (Tb > 37.9°C) mammals are cursorial, including Artiodactyla, Lagomorpha, some large Rodentia, and Carnivora. The ruminant supraendothermic cursorial pulse is putatively associated with global cooling and vegetation changes following the Paleocene–Eocene Thermal Maximum. Reconstructed ancestral body temperatures were highly unrealistic deep within the mammalian phylogeny because of the lack of fossil Tb data that effectively creates ghost lineages. However, it is anticipated that the method of estimating body temperature from the abundance of 13C–18O bonds in the carbonate component of tooth bioapatite in both extant and extinct animals may be a very promising tool for estimating the Tb of extinct mammals. Fossil Tb data are essential for discerning derived Tb reversals from ancestral states, and verifying the dates of supraendothermic pulses.