Discover the Major Animal Groups and What Makes Each One Special

Scientists sort all animals into groups based on their body features. You can learn to identify any animal by looking at its body covering, how it breathes, and how it cares for its young. This is called animal classification.

You already know about Animal Classification and Major Animal Groups now you will go deeper into each group and learn what makes them unique.

Mammals

Mammals have fur or hair on their bodies. They are warm-blooded, which means their bodies stay warm on their own. Most mammals give birth to live young and feed their babies with milk. Examples include bears, dogs, cats, whales, dolphins, and bats.

Birds

Birds are the only animals that have feathers. They also have wings and a beak. Birds are warm-blooded and lay eggs. Examples include eagles, robins, and penguins. Even penguins, which cannot fly, are birds because they have feathers.

Reptiles

Reptiles have dry, scaly skin. They are cold-blooded, which means they need the sun to warm their bodies. Reptiles breathe air with lungs and lay leathery eggs on land. Examples include snakes, lizards, turtles, and crocodiles.

Amphibians

Amphibians are special because they live both in water and on land. They have moist, smooth skin and can breathe through their skin. They usually hatch in water and move to land as they grow. Examples include frogs and salamanders.

Fish

Fish live in water and breathe using gills. They have wet scales on their bodies and use fins to swim. Examples include goldfish and salmon.

Insects

Insects have six legs and three body parts. They have a hard outer covering called an exoskeleton. Most insects hatch from eggs. Examples include butterflies, ants, and beetles. Butterflies and caterpillars are both insects.

Arachnids

Arachnids have eight legs and two main body sections. Spiders are arachnids, not insects, because they have eight legs instead of six.

Crustaceans

Crustaceans are invertebrates with a hard outer shell and jointed legs. Examples include crabs, lobsters, and shrimp.

Vertebrates are animals that have a backbone inside their body. Mammals, birds, reptiles, amphibians, and fish are all vertebrates. Invertebrates are animals that do not have a backbone. Insects, spiders, worms, and crabs are invertebrates.

You can learn more about how animals move and use their bodies in Movement Types: How Different Animals Move.

Warm-blooded animals make their own body heat from inside. Mammals and birds are warm-blooded. Cold-blooded animals get their body heat from the sun or their surroundings. Reptiles, fish, and amphibians are cold-blooded.

Animal Classification: Animal classification is the way scientists sort animals into groups based on their body features and how they live.

Mammal: A mammal is an animal that has fur or hair, is warm-blooded, and feeds its babies with milk. Bears, dogs, and whales are mammals.

Bird: A bird is an animal that has feathers, wings, and a beak. Birds are warm-blooded and lay eggs. Eagles and penguins are birds.

Reptile: A reptile is a cold-blooded animal with dry, scaly skin that breathes air with lungs. Snakes, lizards, and turtles are reptiles.

Amphibian: An amphibian is a cold-blooded animal that lives both in water and on land. Amphibians have moist, smooth skin and can breathe through their skin. Frogs and salamanders are amphibians.

Fish: A fish is a cold-blooded animal that lives in water, has wet scales, and breathes through gills. Goldfish and salmon are fish.

Insect: An insect is an invertebrate with six legs, three body parts, and an exoskeleton. Butterflies, ants, and beetles are insects.

Arachnid: An arachnid is an invertebrate with eight legs and two body sections. Spiders are arachnids.

Crustacean: A crustacean is an invertebrate with a hard outer shell and jointed legs. Crabs, lobsters, and shrimp are crustaceans.

Vertebrate: A vertebrate is an animal that has a backbone inside its body. Mammals, birds, reptiles, amphibians, and fish are all vertebrates.

Invertebrate: An invertebrate is an animal that does not have a backbone. Insects, spiders, worms, and crabs are invertebrates.

Warm-blooded: A warm-blooded animal makes its own body heat from inside its body. Mammals and birds are warm-blooded.

Cold-blooded: A cold-blooded animal cannot make its own body heat and must use the sun to warm up. Reptiles, fish, and amphibians are cold-blooded.

Gills: Gills are special organs that fish use to breathe oxygen from the water. Fish do not need to come to the surface to breathe.

Scales: Scales are small, flat, overlapping plates that cover the bodies of fish and reptiles. Fish have wet scales, and reptiles have dry scales.

Feathers: Feathers are the special body covering found only on birds. Feathers help birds fly and stay warm.

Fur or Hair: Fur or hair is the body covering found on mammals. It helps keep mammals warm.

Exoskeleton: An exoskeleton is a hard outer covering on the outside of an animal's body. Insects and crustaceans have exoskeletons.

Backbone (Spine): A backbone is a row of bones inside an animal's body that supports it. Animals with a backbone are called vertebrates.

You can practice identifying animal groups by looking at body coverings. If you see fur, think mammal. If you see feathers, think bird. If you see dry scales, think reptile. If you see moist smooth skin, think amphibian. If you see wet scales and gills, think fish.

You can also explore External Features: Body Coverings, Limbs, and Sensory Organs to learn even more about how animal bodies look and work.

Before learning about animal groups, you explored Living vs. Non-living Things and what makes something alive. You also learned about Plant Classification and Major Plant Groups, which shows you how scientists sort living things into groups.

You also studied Animal Classification and Major Animal Groups and Movement Types: How Different Animals Move all of these topics help you understand animal diversity.

Now that you know the major animal groups, you are ready to explore more exciting topics. In Animal Adaptations: Physical and Behavioral Features, you will discover how each animal group has special features that help it survive.

You will also learn about Animal Life Cycles: Various Animal Growth Patterns and how animals in different groups grow and change. For example, in Metamorphic Life Cycles: Complete and Incomplete Metamorphosis, you will see how insects like butterflies change completely as they grow. In Non-metamorphic Life Cycles: Direct Development Patterns, you will learn how other animals grow without such big changes.

You can also compare animals to plants by exploring Plant Groups: Major Plant Classifications and Plant Adaptations: Structural Adaptations.

Later, you will use what you know about animal groups to understand Structural Adaptations: Physical Features for Survival, Behavioral Adaptations: Actions That Aid Survival, Communities: Interaction Between Populations, and Ecosystem Components: Living and Non-living Elements.