A Single Origin of Heterothermy in Mammals
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.
KeywordsPlacental Mammal Tree Shrew Close Phylogenetic Relationship Daily Torpor Arctic Ground Squirrel
The research was financed by incentive grants from the University of KwaZulu-Natal and the National Research Foundation, South Africa.
- Flannery T (1995) Mammals of new guinea. Cornell University Press, New YorkGoogle Scholar
- Geiser F, Ruf T (1995) Hibernation versus daily torpor in mammals and birds: physiological variables and classification of torpor patterns. Physiol Zool 68:935–966Google Scholar
- MacLeod N (1996) K/T redux. Paleobiology 22:311–317Google Scholar
- Maddison WP, Maddison DR (2009) Mesquite: a modular system for evolutionary analysis. Version 1.12Google Scholar
- Malan A (1996) The origins of hibernation: a reappraisal. In: Geiser F, Hulbert AJ, Nicol SC (eds) Adaptations to the cold: tenth international hibernation symposium. University of New England Press, Armidale, pp 1–6Google Scholar
- McNab BK, Wright PC (1987) Temperature regulation and oxygen consumption in the Philippine tarsier, Tarsier syrichta. Physiol Zool 60:596–600Google Scholar
- Nelson LE, Asling CW (1962) Metabolic rate of tree shrews, Urogale evertii. Proc Soc Exp Biol Med 46:180–185Google Scholar
- Newman JR, Rudd RL (1978) Observations of torpor-like behavior in shrew, Sorex sinuosus. Acta Theriol 23:446–448Google Scholar
- Schmidt-Nielsen K (1983) Animal physiology: adaptation and environment. Cambridge University Press, CambridgeGoogle Scholar
- Strahan R (1991) Complete book of Australian mammals. Cornstalk, SydneyGoogle Scholar