BIOLOGY · Stage 7 · Chapter 1: Classification and Life

Biology 1.6 Classifying vertebrates

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Biology 1.6 Classifying vertebrates — Alhussan International Academy — Biology (Stages 7–9) notes: Describe the five classes of vertebrates and classify an animal by its features, including unusual vertebrates.Vertebrate = an animal with a backbone, often relatively big because i…

Where found
Five groups
Deciding the group
Amphibians
Metamorphosis
Warm-blooded

Section 1 of 5Vertebrates and their backbone

Vertebrate = an animal with a backbone, often relatively big because it is supported by a bony skeleton.
Where found
- many live on land, so we see them around us every day.
Five groups
- fish, amphibians, reptiles, birds and mammals.
Deciding the group
- observing the outer covering is often a good way, together with breathing, reproduction and body temperature.

Section 2 of 5Fish and amphibians

1Fish3 points

they live in water and have scales covering the body.
They lay eggs in water, breathe with gills and have fins and a tail.
Body temperature varies with the surroundings.

2Amphibians4 points

they live in water and on land at different times in their life cycle.
They have moist, smooth skin, lay eggs in water and have four legs.
They breathe through their skin and their lungs as adults.
Body temperature varies with the surroundings.

3Metamorphosis2 points

a young amphibian changes shape as it becomes an adult, such as a tadpole becoming a frog.
Moist skin is needed for gas exchange, so amphibians live near water.

Section 3 of 5Reptiles, birds and mammals

1Reptiles3 points

they do not need water to breed and have dry scaly skin.
They lay leathery-skinned eggs on land, which stop drying out.
They have four legs (except snakes), breathe air with lungs and have a body temperature that varies with the surroundings.

2Birds4 points

they live on land, although some spend a lot of time on the water, and most can fly.
They all have feathers and beaks, two legs and two wings, even if they cannot fly.
They lay hard-shelled eggs on land and breathe air with lungs.
They control their own body temperature, which stays the same whatever the surroundings.

3Mammals4 points

most live on land, some in water and a few fly.
They all have fur, give birth to live young and make milk to feed them.
They have four limbs, which may form arms (monkeys), flippers (whales) or wings (bats).
They breathe air with lungs and control their own body temperature.

Section 4 of 5The five classes compared

Class	Body covering	Breathing	Reproduction	Temperature
Fish	Wet scales	Gills	Eggs laid in water	Varies with surroundings
Amphibians	Moist, smooth skin	Skin and lungs (adults)	Eggs in water	Varies with surroundings
Reptiles	Dry scales	Lungs	Leathery eggs on land	Varies with surroundings
Birds	Feathers	Lungs	Hard-shelled eggs	Constant (warm-blooded)
Mammals	Fur	Lungs	Live young, fed with milk	Constant (warm-blooded)

Warm-blooded
- animals that keep a constant body temperature using heat from respiration.
Cold-blooded
- animals whose body temperature changes with the environment, so reptiles often bask in the Sun.

Section 5 of 5Unusual vertebrates

Difficulty
- some animals are unusual or have characteristics from more than one group, so several features must be checked.
Armadillo
- leathery scales and a low body temperature suggest a reptile, but soft fur, live young and milk make it a mammal.
Bat
- a mammal with wings of skin, fur and milk, not a bird.
Whale
- it lives in the sea and has fins but breathes air, is warm-blooded and gives milk, so it is a mammal.
Snake
- a reptile with no legs, dry scales and leathery eggs.
Penguin
- a bird that cannot fly but has feathers and lays eggs.
Platypus
- a mammal that lays eggs but has fur and feeds milk to its young.
Rule
- decide on the combination of features and not on where the animal lives or whether it flies.

Last updated: 13 October 2026