Eurytherm

A eurytherm is an organism, often an endotherm, that can function at a wide range of ambient temperatures. To be considered a eurytherm, all stages of an organism's life cycle must be considered, including juvenile and larval stages. These wide ranges of tolerable temperatures are directly derived from the tolerance of a given eurythermal organism's proteins. Extreme examples of eurytherms include Tardigrades (Tardigrada), the desert pupfish (Cyprinodon macularis), and green crabs (Carcinus maenas), however, nearly all mammals, including humans, are considered eurytherms. Eurythermy can be an evolutionary advantage: adaptations to cold temperatures, called cold eurythermy, are seen as essential for the survival of species during ice ages. In addition, the ability to survive in a wide range of temperatures increases a species' ability to inhabit other areas, an advantage for natural selection.

Eurythermy is an aspect of thermoregulation in organisms. It is in contrast with the idea of stenothermic organisms, which can only operate within a relatively narrow range of ambient temperatures. Through a wide variety of thermal coping mechanisms, eurythermic organisms can either provide or expel heat for themselves in order to survive in cold or hot, respectively, or otherwise prepare themselves for extreme temperatures. Certain species of eurytherm have been shown to have unique protein synthesis processes that differentiate them from relatively stenothermic, but otherwise similar, species.