|Among the features that distinguish mammals from the other amniotes, the reptiles 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 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 Eutheria, have a placenta which feeds the offspring during pregnancy.
Except for the five species of monotremes (egg-laying mammals), all modern mammals give birth to live young.
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|Marsupials and kin||Placentals and kin|
|Monotremes and kin||†Tingamarra|