Inc. Mammals are fur-bearing animals that are capable of internal temperature regulation. With only a few exceptions, female mammals give birth to live young and feed their offspring milk from mammary glands.
Mammals have the largest brains in relation to body size of any vertebrate.
This places a severe limitation on offspring development at birth, since many females are to small to give birth to highly developed young, instead most mammals invest in long periods of parental care. Unlike reptiles, the mammal lower jaw is composed of a single bone, and the jaws contain 4 specialized types of teeth, the incisors, canines, premolars, and molars. Mammals have 3 middle-ear bones that set up a chain of vibrations that are transmitted across a membrane to nerve receptors in the fluid filled inner ear. Mammals have been evolving and diversifying since the Triassic Period when they arose from the Synapsidae , a primitive group of amniote vertebrates. The first mammals appeared soon after the dinosaurs, about 230 million years ago.