Fig 2. Relationship between Tlc (°C) and body mass (g) in mammals.
The Tlc is defined as the ambient temperature below which the rate of metabolic heat production must be increased in order to maintain homeothermy. Of all species with Tlc above the global mean surface temperature (14°C, horizontal dashed line; [11]), humans (Tlc range from 23 to 33°C; [16,17]) are the most massive, and of all species with a body mass above 50 kg (vertical dashed line), humans have the highest Tlc. For clarity, the figure includes only data for a limited number of taxa (humans, Carnivora, nonhuman primates, Rodentia, ruminants). However, the shape of the relationship between body mass and Tlc does not change when data for other groups are included (Chiroptera, Cingulata, Dasyuromorphia, Diprotodontia, Erinaceomorpha, Eulipotyphla, Hyracoidea, Lagomorpha, Macroscelidea, Monotremata, Peramelemorphia, and Soricomorpha). Species data indicated by silhouettes are, clockwise from the left, for voles (M. arvalis), mice (M. musculus), humans, and reindeer (R. tarandus). Data from [12,13,18,19]. Tlc, lower critical temperature.