Mammals include any animal of the Mammalia, a large class of warm-blooded vertebrates having mammary glands in the female, a thoracic diaphragm, and a four-chambered heart. The class includes the whales, carnivores, dolphins, porpoises, rodents, bats, primates, etc.

Mammals have the body more or less covered with hair, nourish the young with milk from the mammary glands, and, with the exception of the egg-laying monotremes, give birth to live young.