Evolution has it that mammals evolved from reptiles. As explained by Klappenbach on ‘An Introduction to Mammals,’ mammals evolved from “a group of reptiles known as Therapsids.” The adaptations that mammals acquired in favor of their reptile ancestors, is the ability to control their body temperature or a situation known as endothermy. Apart from a few egg-laying mammals, most mammals have evolved to give birth to live young ones that are nourished with milk from the mammary glands.
Reptiles lack mammary glands. Mammals have also managed to colonize both water land and therefore acquired various adaptations to survive on land effectively. This can be observed in the locomotion of sea mammals such as the whale and land mammals, some of which are bipeds and others quadrupeds. Some like the bats are adapted to flight. Mammals have also evolved mechanisms to control vasoconstriction and vasodilatation as a way of conserving heat. This mechanism ensures that heat carried in the blood is restricted from flowing to areas exposed to cold to conserve heat.
According to Wikipedia on ‘Endothermic’, mammals also have in their brain an area called the hypothalamus that regulates body temperature. This is achieved by either increasing or decreasing metabolic processes in the body that are responsible for heat generation. Some mammals that live in water and extremely cold conditions have layers of fat underlying the skin to prevent excessive heat loss. Furthermore, other temperature regulation techniques are behavioral and include hibernation and aestivation.