2.7 CLASSIFYING ANIMALS - VERTEBRATES

Vertebrates are animals with backbones. There are over 40 000 different kinds of vertebrates and more than half of them are fish. The other main classes are amphibians, reptiles, birds and mammals. The keys below and on the next page show how we can sort them out.

Fish are covered in scales and have fins. They live in water and breathe through gills. They range in size from certain sharks, which can grow up to 18 m long, to tiny fresh water fish called gobies, which measure only a few mm. Most fish are good to eat, so fish like Tilapia and Carp are farmed in many countries.

Reptiles are also covered in scales but have no fins. All reptiles except snakes have four legs. Most reptiles live on the land including many kinds of lizards. Turtles live in the sea, but come to the land to lay their eggs. Reptiles are generally harmless, but a few are dangerous. Crocodiles may attack and eat people and some snakes have very poisonous bites. Some large snakes such as pythons squeeze their prey to death.

Blue whale Toad

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Birds are covered in feathers except for their legs, which are scaly. They have a beak for a mouth and wings instead of front legs. Most birds can fly, except for a few very large ones like the ostrich and the emu. Ostriches can be over 2½ m tall, but some humming birds are less than 6 cm long. Peregrine falcons are the fastest fliers. They can reach speeds of 290 km/h when diving on prey. We keep the domestic fowl for food and for its eggs, which are good to eat.

Amphibians have smooth skins that they like to keep cool and damp. They have four legs and webbed feet, and lay their eggs in water. Frogs and toads are amphibians. They have very strong back legs. Some frogs can jump over 5 m.

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Mammals usually have hair or fur covering all or part of their skin. Female mammals have milk glands for feeding their young. Most mammals live on land and have four legs, or two legs and two arms. A few mammals such as whales and dolphins live in the sea and have flippers instead of legs. We keep mammals such as sheep, goats and cattle for food and we sometimes use their skin for clothing. Some mammals are also used for riding or pulling loads.

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  • 1. From the key, what three things do all fish have?
  • 2. Do each of the following have (i) a backbone, (ii)

scales? toad, centipede, snake, goby, hen, whale.

  • 3. Try to list all the ways people use mammals.

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A simple key to animals (vertebrates)

ANIMALS

animals have backbones animals have no backbones

VERTEBRATES INVERTEBRATES

(See Module 2.6)

body covered in scales body not covered in scales

animals have fins animals have no fins body covered in feathers body not covered in feathers

FISH REPTILES BIRDS

eg shark, tuna, Tilapia eg snake, lizard, turtle eg vulture, parrot, hen, finch

animals have fur or hair animals have smooth skin

MAMMAL AMPHIBIAN

eg cow, dog, rat, whale eg frog, toad

  • 4. What kind of animal is this?

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