In 1986, J. Scott Turner and C. Richard Tracy proposed that the evolution of a sail in "Dimetrodon" was related to the evolution of warm-bloodedness in mammal ancestors. They thought that the sail of "Dimetrodon" enabled it to be homeothermic, maintaining a constant, albeit low, body temperature. Mammals are also homeothermic, although they differ from "Dimetrodon" in being endothermic, controlling their body temperature internally through heightened metabolism. Turner and Tracy noted that early therapsids, a more advanced group of synapsids closely related to mammals, had long limbs which can release heat in a manner similar to that of the sail of "Dimetrodon". The homeothermy that developed in animals like "Dimetrodon" may have carried over to therapsids through a modification of body shape, which would eventually develop into the warm-bloodedness of mammals.