subject: What Are Mammals [print this page] Human beings are mammals, and so are all furry animals whose young are born alive and fed with milk from the mother's body until they areold enough to feed themselves. Thereare other ways in which all mammals are alike. They arc warm-blooded animals, which means that the body itself keeps the blood warm; birds arc- also warm-blooded, but fish and snakes and other reptiles are cold-blooded, and the temperature of their blood depends on the temperature of the air or water around them. Human beings are mammals that walk on tw o legs and are called bipeds.
Nearly all the others walk on four legs, and are called cjuadrupec!s. Most mammals are covered with fur, and all have more or less hair on their bodies, although men have the least of all. Whales, porpoises, and dolphins, although they livein the ocean and swim about like fish, are mammals, have milk for their young, and must breathe air. Even when they sleep, they do not keep their noses under water for long. These strange mammals look much like fish. Another peculiar mammal is the platypus, or duckbill.
This animal lays eggs, as a bird does, but is covered with fur. It nurses its young after they hatch, and there is no doubt that it is a mammal. These strange creatures, and also the echidnas, the only other egg-laying mammals, livein Australia and Tasmania.The mammalian line of descent diverged from an amniote line at the end of the Carboniferous period. One line of amniotes would lead to reptiles, while the other would lead to synapsids. According to cladistics, mammals are a sub-group of synapsids.
