Kingdom Animalia: animals with a backbone

Animals with a backbone

All the animals so far had no backbone. Now we turn to the Chordata: animals with a notochord, a rod along the back, at some time in their life. In the Vertebrata, the notochord is replaced by a backbone (vertebral column), which gives support. The vertebrates have a brain in a skull, a spinal cord, and a heart.

There are five classes of vertebrates.

Pisces: fish

Fish live in water. They have scales and fins, and they breathe with gills. The heart has two chambers. They are cold-blooded: their body temperature changes with the water. They lay eggs. Examples: rohu, shark.

Amphibia

Amphibians can live in water and on land. The skin is moist, with no scales. The young (tadpole) breathe with gills. The adult breathes with lungs and also with the skin. The heart has three chambers. They are cold-blooded and lay eggs in water. Examples: frog, toad, salamander.

Reptilia

Reptiles have dry skin with scales. They breathe with lungs. The heart has three chambers (four in the crocodile). They are cold-blooded. They lay eggs with a tough shell on land. Examples: lizard, snake, turtle, crocodile.

Aves: birds

Birds have feathers, and their front limbs are wings. They have four-chambered hearts, and they are warm-blooded. They breathe with lungs and have light, hollow bones. They lay eggs with a hard shell.

Mammalia

Mammals have hair on the skin, and mammary glands that make milk for the young. They have four-chambered hearts, and they are warm-blooded. Most give birth to live young. A few, like the platypus, lay eggs. A whale lives in the sea, and a bat flies, but both are mammals.

Cold-blooded and warm-blooded

You should find that on a cold morning at $5\ ^\circ\text{C}$, the lizard's body is at $5\ ^\circ\text{C}$ too. The pigeon keeps a gap of $36\ ^\circ\text{C}$, and it pays for that gap with food.

Why does the heart matter?

The more chambers in the heart, the better it keeps blood rich in oxygen apart from blood poor in oxygen. A four-chambered heart keeps them completely apart. It supports a warm-blooded body that needs a lot of energy.

Try it in Python

This program is a key to the classes of vertebrates. It uses the number of chambers in the heart and the skin.

Practise with new numbers

Common mistakes

• Calling a whale a fish. It breathes with lungs and feeds its young on milk. It is a mammal.
• Calling a bat a bird. It has hair, not feathers. It is a mammal.
• Thinking cold-blooded means cold. A lizard in the sun can be warm. Its body simply follows the air.
• Giving every reptile three chambers. The crocodile has four.

Remember these

• Vertebrates: Pisces (2-chambered heart), Amphibia (3), Reptilia (3), Aves (4), Mammalia (4).
• Birds and mammals are warm-blooded. The other three classes are cold-blooded.
• Fish breathe with gills. Amphibians use gills when young and lungs as adults.
• A whale and a bat are mammals.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Which class has feathers?

2. Which class has a heart with two chambers?

3. Is a whale a fish?

4. On a cold morning at $8\ ^\circ\text{C}$, which moves more slowly, a lizard or a sparrow? Why?