What makes an animal a mammal?

Compared to the over 21,000 kinds of fish and over 800,000 kinds of insects in the world, though, mammals make up a fairly small group of animals. Mammals range from the very tiny Kitti's hog-nosed bat that weighs less than an ounce to the extremely huge blue whale that can weigh as much as 150 tons. read more

Mammals are a particular class of animal. What makes an animal a mammal are several things. First, they must have glands that give milk. This is to feed their babies. Second, they are warm-blooded. Third, all mammals have fur or hair. Humans are mammals and so are dogs, whales, elephants, and horses. read more

Mammals have hair or fur; are warm-blooded; most are born alive; the young are fed milk produced by the mother’s mammary glands; and they have a more complex brain than other animals. read more