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Scientists expect endotherm animals -- animals that can regulate their own body temperature, like mammals -- to be able to protect themselves against fluctuating temperatures because they can maintain a constant body temperature.

However, in a first-of-its-kind study of "warm-blooded" endotherms, a University of Illinois Urbana-Champaign team found tropical birds can handle thermal variation just fine.

Some of the most famous sharks, like the white shark or the extinct megalodon, are unusual in being among the mere ~1% of shark species to be considered warm-blooded or "regional endotherms."

David and his colleagues used inner-ear shape and size as a proxy for an animal’s body temperature and behavior to determine when mammals started to become endotherms.

Muscles work better if they’re warm, so one advantage that endotherms enjoy is the ability to spring into action at a moment’s notice.