Mammals (class Mammalia (pron.: /məˈmeɪli.ə/)) are a clade of warm-bloodedamniotes. Among the features that distinguish them from the other amniotes, thereptiles and the birds, are hair, three middle ear bones, mammary glands in females, and a neocortex (a region of the brain). 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 rorqual whales, as well as the most intelligent such as elephants as well as some primates and 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 millimeter (1- to 1.5-inch)bumblebee bat to the 33-meter (108-foot) blue whale.