Mammal
Mammals are a clade of endothermic amniotes distinguished from the reptiles and the birds by the possession of hair, three middle ear bones, mammary glands in females, and a neocortex. The mammalian brain regulates body temperature and the circulatory system, including the four-chambered heart. The mammals include the largest animals on the planet, the rorquals and some other whales, as well as some of the most intelligent, such as elephants, some primates and some cetaceans. The basic body type is a four-legged land-borne animal, but some mammals are adapted for life at sea, in the air, in the trees, or on two legs. The largest group of mammals, the placentals, have a placenta which feeds the offspring during pregnancy. Mammals range in size from the 30–40 mm bumblebee bat to the 33-meter blue whale. The word "mammal" is modern, from the scientific name
Mammalia coined by Carl Linnaeus in 1758, derived from the Latin
mamma. All female mammals nurse their young with milk, which is secreted from special glands, the mammary glands. According to
Mammal Species of the World, 5,416 species were known in 2006.