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.

Birds - Although not all birds can fly, their basic design and main characteristics resolve around adaptations for flight. All birds are covered with feathers. Flighted birds have partially hollow bones that are lightweight but strong and a very efficient respiratory system. All birds hatch from eggs, have two wings and two feet and are warm-blooded (endothermic) vertebrates.