What are vertebrates?
Vertebrates are animals that have a backbone (also called the vertebral column or spine). It is made of many small bones called vertebrae. It protects the spinal cord, a thick bundle of nerves. Vertebrates also have a skull that protects the brain.
Animals without a backbone, like insects, worms and snails, are invertebrates. Vertebrates are a group of the chordates.
Five features help us tell the groups apart: body covering, breathing organ, heart chambers, blood temperature and how the young are born.
Fish and amphibians
Fish live in water. They have scales, fins and a streamlined body. They breathe with gills. Their heart has 2 chambers. They are cold-blooded and most lay eggs in water. Examples: rohu, shark, seahorse.
Amphibians live part of life in water and part on land (amphi = both). Their skin is smooth and moist and has no scales. Young ones (tadpoles) breathe with gills; adults breathe with lungs and through the skin. The heart has 3 chambers. They lay soft eggs in water. Examples: frog, toad, salamander.
Reptiles and birds
Reptiles have dry skin covered in scales that stops them losing water, so they can live in dry places. They breathe with lungs. The heart has 3 chambers (a crocodile has 4). They are cold-blooded and lay eggs with a leathery shell on land. Such eggs let the baby grow without water around it, so reptiles, birds and mammals are called amniotes. Examples: lizard, snake, turtle, crocodile.
Birds have feathers, wings and a beak, and light hollow bones. Most can fly. They breathe with lungs and air sacs. The heart has 4 chambers. They are warm-blooded and lay hard-shelled eggs. Examples: crow, peacock, penguin.
Mammals
Mammals have hair or fur and feed their babies with milk made in mammary glands. They breathe with lungs, have a 4-chamber heart and are warm-blooded. Most give birth to live young. A few, such as the platypus, lay eggs. Examples: cow, whale, bat, human.
Warm-blooded and cold-blooded
Warm-blooded animals (birds, mammals) keep their body at a steady, warm temperature. Cold-blooded animals (fish, amphibians, reptiles) take their temperature from the surroundings, so a lizard sits in the sun to warm up.
Try it
In the 3D: in the last step press each group. Count how many red and blue heart pieces you see. Which two groups have 4?
At home: make a table with five rows (fish to mammal) and four columns (covering, breathing, heart, blood). Fill it from memory first, then check. Then find one animal around you for each row.
Key formulas and definitions
- Vertebrate = has a backbone (vertebral column)
- Five classes: Fish, Amphibians, Reptiles, Birds, Mammals
- Heart chambers: fish 2, amphibians 3, reptiles 3 (crocodile 4), birds 4, mammals 4
- Warm-blooded: birds, mammals. Cold-blooded: fish, amphibians, reptiles
- Breathing: fish gills; amphibians skin and lungs; reptiles, birds, mammals lungs
Worked examples
1. A snake has dry scaly skin, lungs and lays leathery eggs on land. Which class?
Reptile. Dry scales, lungs and leathery eggs on land are reptile features.
2. A bat flies, but has fur and feeds its babies milk. Bird or mammal?
Mammal. Hair and milk are mammal features. A bat flies with wings of skin, not feathers.
3. A water animal breathes with gills and has a 2-chambered heart. Which class?
Fish. Gills and a 2-chamber heart are fish features. A whale lives in water too, but it has lungs and milk, so it is a mammal.
Common mistakes
- Calling a whale or dolphin a fish. They breathe with lungs and feed milk, so they are mammals.
- Thinking that a frog has scales. Its skin is smooth and moist.
- Saying that all animals that fly are birds. Bats are mammals.
- Mixing up heart chambers. Remember 2, 3, 3, 4, 4.