Mesotherm

A mesotherm (from Greek μέσος mesos "intermediate" and thermē "heat") is a type of animal with a thermoregulatory strategy intermediate to cold-blooded ectotherms and warm-blooded endotherms. Mesotherms have two basic characteristics: Elevation of body temperature via metabolic production of heat. Weak or absent metabolic control of a particular body temperature. The first trait distinguishes mesotherms from ectotherms, the second from endotherms. For instance, endotherms, when cold, will generally resort to shivering or metabolizing brown fat to maintain a constant body temperature, leading to higher metabolic rates. A mesotherm, however, will experience lower body temperatures and lower metabolic rates as ambient temperature drops. In addition, mesotherm body temperatures tend to rise as body size increases (a phenomenon known as gigantothermy), unlike endotherms. This reflects the lower surface area to volume ratio in large animals, which reduces rates of heat loss. While extant mesotherms are relatively rare, good examples include tuna, lamnid sharks (e.g., the great white shark), the leatherback sea turtle, some species of bee, naked mole rats, hyraxes, and echidnas. Historically, the same word was used by de Candolle to describe plants that require a moderate degree of heat for successful growth. In his scheme, a mesotherm plant grew in regions where the warmest month had a mean temperature greater than and the coldest month had a mean temperature of at least . The thermoregulatory status of dinosaurs has long been debated, and is still an active area of research. The term 'mesothermy' was originally coined to advocate for an intermediate status of non-avian dinosaur thermoregulation, between endotherms and ectotherms. A more technical definition was provided by Grady et al, who argued for dinosaur mesothermy on the basis of their intermediate growth rates, and the empirical relationship between growth, metabolism and thermoregulation in extant vertebrates.