Animal World

The world is full of animals. They can be classified, or grouped. Read about four groups below.

Salmon are fish.

Fish live in water. Fins help them swim. Gills help them breathe. Most fish are covered in scales × scale FAUZAN MAUDUDDIN—EYEEM/GETTY IMAGES a small, thin plate that helps form a covering for the bodies of some animals (noun) Snakes have scales. .

Robins are birds.

Birds have feathers. Most birds have strong muscles. These muscles help birds fly. Birds hatch × hatch to be born by coming out of an egg (verb) Let's watch a chick hatch from an egg. from eggs. They eat with their beaks.

Frogs are amphibians.

Amphibians are cold-blooded animals. Their body temperature changes with their environment × environment PATRICK J. ENDRES—GETTY IMAGES surroundings (noun) Polar bears live in cold environments. . Amphibians live in water and on land.

Bears are mammals.

Mammals are warm-blooded animals. Body fat and fur help mammals stay warm. Mother mammals feed their babies milk from their bodies. Humans are mammals too!

Did You Know?

Not all birds can fly. The ostrich is the largest bird in the world. Its wings are too weak to fly. It uses its strong legs to walk and run.