There are millions of different kinds of animal on Earth β so how do scientists keep track of them all? They sort them into groups, by looking at what their bodies have in common. Here are ten facts about the animal groups, and where to find out more about the animals in each one.
1. Animals are grouped by their bodies, not where they live.
Scientists sort animals by what they are like β fur or feathers, a backbone or not, how they breathe. That is why a whale, which lives in the sea, isnβt a fish: it breathes air and feeds its babies milk, just like a cat does.
2. Most kinds of animal have no backbone at all.
Animals with a backbone are called vertebrates. Animals without one are invertebrates β insects, spiders, worms, snails and jellyfish. There are far more kinds of invertebrate on Earth than any other sort of animal.
3. Mammals have hair and feed their babies milk.
Most give birth to live young rather than laying eggs. You can meet lots of mammals in our Top 10s: cats, dogs, lions, pandas, gorillas, giraffes, polar bears, sloths and bats.
4. You are a mammal too.
Humans have hair, breathe air and feed their babies milk, so we belong in the mammal group with cats and gorillas. People are animals β just very unusual ones.
5. Birds have feathers, and every one hatches from an egg.
Not every bird can fly: penguins swim instead, and ostriches run. Find out more in our Top 10 Facts About Birds.
6. Fish breathe underwater through gills.
Gills take oxygen out of the water, so most fish never need to come up for air. Most fish are covered in scales and swim with fins. Read more in our Top 10 Facts About Fish.
7. Reptiles have dry, scaly skin.
They canβt make their own body heat, so you will often find them warming up in the sun. Lizards and snakes are reptiles, and so are crocodiles and tortoises.
8. Amphibians live two lives.
Most frogs, toads and newts start life in water, breathing through gills like a fish. As they grow, their bodies change so they can live on land as well. That change is called metamorphosis.
9. Insects always have six legs.
Their bodies come in three parts: the head, the thorax and the abdomen. Bees are insects, and so are most of the creepy-crawlies in our Top 10 Facts About Bugs.
10. Spiders arenβt insects.
They have eight legs, not six, and only two body parts. Spiders belong to a group called arachnids, along with scorpions. Discover more in our Top 10 Facts About Spiders.
π Words to know
- Classify
- To sort things into groups by what they have in common.
- Vertebrate
- An animal with a backbone, like a mammal, bird, fish, reptile or amphibian.
- Invertebrate
- An animal without a backbone, like an insect, a spider or a worm.
- Gills
- What fish use to breathe. They take oxygen out of the water.
- Live young
- Babies that are born rather than hatching from an egg. Most mammals have live young.
β οΈ Watch out!
How much do you know about animal groups?
What are the two main groups scientists sort animals into?
- Vertebrates and invertebrates
- Big and small
- Land and sea
- Wild and pets
A whale lives in the sea. Which group does it belong to?
- Mammals
- Fish
- Reptiles
- Amphibians
How many legs does an insect have?
- Six
- Eight
- Four
- Ten
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