Living in a Seasonal World

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A Single Origin of Heterothermy in Mammals

  • Barry G. LovegroveAffiliated withSchool of Life Sciences, University of KwaZulu-Natal Email author 

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Some mammal lineages survived the global fires that occurred in the hours following the asteroid impact at Chicxulub, Yucatan, at the Cretaceous/Tertiary Boundary (K/T Boundary) 65 mya. Several studies have proposed that it was the capacity for torpor and refuge underground, in tree holes, caves, and underwater, that ensured the short- and long-term survival of the post-impact conditions. Here I test the hypothesis that heterothermy was a pleisiomorphic condition in ancestral mammals which allowed certain mammal lineages to survive the K/T Boundary. I employed a maximum likelihood approach to reconstruct the likely heterothermic status of the last mammalian ancestor. With our current knowledge, the probability of heterothermy (58%) slightly exceeds that of no heterothermy. However, if some mammals that have yet to be studied, but which have been identified as highly likely heterotherms, are scored as heterotherms, the proportional likelihood of heterothermy in ancestral mammals exceeds the 96% probability. At the least, these data confirm that there was single origin of heterothermy in mammals, but further research is required to determine how extensive heterothermy was in Mesozoic mammals.