How are a dog and a lizard alike? What is the same about an octopus and an ant? Do spiders and sponges have something in common? Find out in this lesson about animal classification.

What is Animal Classification?

When you are hungry, you probably think about the kinds of foods you like to eat. Maybe you feel like eating fruit, so you might take a bite of an apple or peel an orange. You may prefer to eat meat, like a piece of chicken or hot dog. Or maybe you have a taste for something sweet like a cookie or slice of cake. No matter what you decide, all of your choices are types of food, whether they are in the fruit group, meat group, sweets group, or another group.

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Just as we put foods into different groups, scientists have also made a way to group, or classify, animals so they are easier to study and talk about. Animal classification is putting animals into different groups depending on how they are alike.

Dogs, rabbits and humans are types of mammals. Frogs, toads, and salamanders are amphibians. A few kinds of reptiles include lizards, snakes and turtles. All birds and fish with bones are vertebrates.
Picture of a dog, bird, fish, frog, and lizard

Backbone or No Backbone?

Even though millions of different kinds of animals live on the earth, all of them can be put into just two main groups: vertebrates and invertebrates. Vertebrates have a backbone. Think of your long, bony spine, which goes from your neck all the way down your back. You are a vertebrate!

Invertebrates are animals that do not have a backbone. Sometimes they have a hard skin around their body to protect them, but invertebrates do not have a spine like you do.


Can you think of some pets or other animals that have backbones? A cat, horse, and hamster are examples. Vertebrates can be sorted even further into five smaller classifications: mammals (animals that have hair or fur, including humans), birds, fish, amphibians, and reptiles. All of them have backbones.

The grasshopper, sponge, lobster, spider, octopus, and butterfly are invertebrates.
Picture of a grasshopper, sea sponge, lobster, spider, octopus, and butterfly


You already know many kinds of invertebrates, or animals that do not have a backbone. In fact, most of all the animals in the world are invertebrates! If you’ve ever had a fly buzzing around your head, you’ve seen an invertebrate. The crickets you might hear chirping at night are also invertebrates. So many different kinds of invertebrates exist that it is difficult to put them into just a few groups, but some of the most common invertebrates are crabs, centipedes, ants, spiders, honey bees, grasshoppers, sponges that grow in the ocean, star fish, and earthworms.

Lesson Summary

Animal classification is when scientists organize animals into groups and sort them by what they have in common, so they can be easier to study. All animals are either vertebrates, animals with a backbone, or invertebrates, animals without a backbone. There are five groups of vertebrates, including mammals, birds, fish, amphibians, and reptiles. Most animals on the earth are invertebrates, and some examples include insects, worms, and many animals that live in the ocean, like the octopus and lobster.