What are reptiles?
Reptiles are vertebrates (animals with a backbone) that crawl or creep. The word 'reptile' comes from a Latin word meaning 'to creep'.
Examples: lizard, chameleon, snake, turtle, tortoise, crocodile, alligator.
Main features
- Dry skin with scales. Scales save water, so reptiles can live in deserts. Snakes shed the old skin from time to time; this is called moulting.
- Lungs. They always breathe air with lungs.
- Cold-blooded. Body temperature changes with the air. A reptile sits in the sun to get warm and goes in shade to cool down.
- Eggs with a leathery shell. Most lay eggs on land. A few snakes and lizards give birth to live young.
- Heart. Three chambers in most reptiles; crocodiles have four.
Four groups of reptiles
- Lizards (house gecko, chameleon, monitor lizard): four legs, most have a tail that can break off and grow back.
- Snakes: no legs, long body, no eyelids. They smell with the tongue. Only some are poisonous.
- Turtles and tortoises: a hard shell on the back. Turtles live in water, tortoises on land.
- Crocodiles and alligators: big strong jaws, long tail, live near rivers and lakes.
Reptiles versus amphibians
Both are cold-blooded. But amphibians have wet bare skin and soft eggs in water, and they breathe with gills when young. Reptiles have dry scaly skin, shelled eggs on land and breathe with lungs from birth. This is why reptiles can live far from water.
Try it
In the 3D, set the air to 10 degrees and watch the reptile. Then set it to 35 degrees. Write down how much faster it moves. At home, watch a lizard on a wall in the morning and again at noon, and compare how fast it runs.
Key formulas and definitions
- Reptile = creeping vertebrate
- Dry scaly skin + lungs + shelled eggs on land + cold-blooded
- Four groups: lizards, snakes, turtles and tortoises, crocodiles
- Body temperature of a cold-blooded animal follows the air temperature
Worked examples
1. Why can a reptile live in a desert but a frog cannot?
A reptile has dry scaly skin that keeps water in, and its eggs have a shell. A frog needs wet skin and lays eggs in water.
2. A lizard is slow at 8 a.m. and quick at noon. Why?
It is cold-blooded. In the morning the air is cool, so the body is cool and slow. By noon the sun has warmed the body and it moves quickly.
3. Name the group each belongs to: gecko, cobra, tortoise, alligator.
Gecko: lizard. Cobra: snake. Tortoise: turtles and tortoises. Alligator: crocodile group.
Common mistakes
- Thinking snakes are slimy. Their skin is dry and smooth.
- Saying all reptiles lay eggs. Most do, but some snakes and lizards give birth to live young.
- Calling reptiles cold animals. Cold-blooded means body heat depends on the air; in the sun they can be warm.
- Mixing up turtle and tortoise. Turtles live mostly in water; tortoises live on land.