Mammals are the most highly developed group of vertebrates:

• Like birds, they are warm blooded or homeothermic.
• They have efficient respiratory and circulatory systems.
• They have highly developed senses.
• They are quick learners.

The young mammal develops inside its mother's womb. When the young mammal is born, it gains energy by drinking its mother's milk. 

Mammals have adapted to life everywhere in the world. The most common groups of mammals include bats, whales, canines, felines, rodents, cloven-hoofed animals and primates. 

List of mammal species