An animal class is made up of animals that are all alike in important ways. Scientists have grouped animals into classes to make it easier to study them.

There are many different animal classes and every animal in the world belongs to one of them. The six most important classes are mammals, birds, fish, reptiles, amphibians and invertebrates.

Mammals
Mammals are warm-blooded (endothermic) vertebrates that have hair or fur and have mammary glands that produce milk to nourish their young. The astonishing diversity among mammals ranges from tiny field mice the size of a thimble to the massive blue whale. Mammals occupy all continents and can live on land, below ground, in trees, in the air and in fresh or salt water. Humans are members of the mammal family.