Mammals breathe air with lungs. Mammals maintain a constant high body temperature independent of their surroundings. Mammals have a four-chambered heart. As a rule, mammals bear live young.
Mammals nurse their young with milk.
Mammals have hair, at least at some stage in their development. The scientific order Cetacea includes all whales. The word Mysticeti is derived from the Greek word for moustache, mystax. It may refer to the hairy appearance of the baleen plates, which baleen whales have instead of teeth. Baleen whales have two external blowholes and are larger in size than most toothed whales.