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Explorers Science

Science · Life cycles

Classify animals

Mammals, birds, fish, reptiles, insects.

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What are the five big animal groups?

Scientists sort animals into groups to help us understand them better. The five main groups are mammals, birds, fish, reptiles, and insects. Each group has special features that make them different from the others. Learning these features helps us know which group an animal belongs to.

Mammals

Mammals have fur or hair on their bodies. They feed their babies milk from their bodies. Most mammals give birth to live babies, not eggs. Humans, dogs, cats, whales, and bats are all mammals. Mammals are warm-blooded, which means their bodies stay the same temperature.

Birds

Birds have feathers covering their bodies and wings. They lay eggs with hard shells. Most birds can fly, but some cannot. Penguins and ostriches are birds that cannot fly. All birds have a beak instead of teeth. Birds are also warm-blooded.

Fish, reptiles, and insects

Fish live in water and breathe through gills. They have scales and fins. Reptiles have dry, scaly skin and most lay eggs. Snakes, lizards, and turtles are reptiles. Insects have six legs and three body parts. Many insects have wings. Butterflies, ants, and bees are insects.

Worked examples

  1. 1. Is a dolphin a fish or a mammal?

    1. Think about where dolphins live. They live in water like fish.
    2. But dolphins breathe air with lungs, not gills like fish do.
    3. Dolphins have smooth skin, not scales. They feed babies milk.
    4. Dolphins are mammals, not fish, even though they live in water.

  2. 2. Why is a penguin a bird even though it cannot fly?

    1. Look at the penguin's body. It has feathers covering it.
    2. Penguins lay eggs with hard shells, just like other birds.
    3. Penguins have wings, even though they use them for swimming.
    4. Having feathers and laying eggs makes penguins birds, not fish.

  3. 3. Is a spider an insect?

    1. Count the legs on a spider. Spiders have eight legs.
    2. Insects only have six legs, not eight legs.
    3. Spiders have two body parts. Insects have three body parts.
    4. Spiders are not insects. They belong to a different group.

Try it yourself

A crocodile has scaly skin and lays eggs on land. Which group does it belong to?

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