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Australian Animal Classifications
The Animal Kingdom

The animal kingdom is so crowded with thousands of wonderful species, so biologists have divided the animals into 6 broad groups to make it easier to understand. The groups are: 

Invertebrates
Reptiles
Fish
Birds
Amphibians
Mammals


Invertebrates:
These are animals without backbones. They include insects, spiders, corals, octopuses, crabs, jellyfish, starfish, worms, millipedes and snails. Invertebrates live in every habitat and come in countless shapes and sizes, from microscopic single celled animals to giant squid more than 20 metres long. They were the first animals on Earth and evolved in the oceans about 800 million years ago. More than 225,000 land invertebrates have been discovered in Australia, but scientists believe there are at least one million invertebrate species in Australia.

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Reptiles:
These are animals that:
  • Have dry scaly skin.
  • Breathe air with lungs.
  • Are cold blooded and cannot keep their body temperature constant.
Snakes, lizards, crocodiles and turtles are all reptiles, and the dinosaurs were reptiles. They usually lay eggs, although a few snakes and lizards give birth to live young. Only sea snakes, crocodiles, turtles and tortoises live in the water. Reptiles evolved from the amphibians, and first appeared on Earth about 300 million years ago. There are around 6000 species in the world today, and Australia has 725 different species.

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Fish:
These are animals that:
  • Have scales and fins to help them swim.
  • Have gills to absorb oxygen from the water, and some have lungs as well.
  • Are cold blooded and cannot keep their body temperature constant.
Fish live in the oceans and in freshwater rivers and lakes, and have an amazing variety of forms, from streamlined sharks to stiff, bony seahorses. They are adapted to live in water, but some, like freshwater eels, are able to move on land between waterholes. Some fish can survive droughts by burrowing deep into the mud and breathing air. Fish were the first animals to have backbones (vertebrates), and evolved from the invertebrates (animals without backbones) 500 million years ago. There are about 21,000 species of fish in the world. Australia has about 200 different freshwater fish and more than 2000 species of saltwater fish in the oceans.

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Birds:
These are animals that:
  • Lay eggs with hard shells.
  • Have feathers and a hard bill.
  • Keep their body temperature constant.
  • Breathe air with lungs.
Birds have very light hollow bones and wings instead of front legs. Most can fly, although penguins have flippers instead of wings, and are able to swim very fast. A few ground-living birds like the emu and cassowary are good runners. They have small wings and are unable to fly. Birds shed (moult) most of their feathers every year and grow new ones to replace them. The first birds evolved from small running reptiles (dinosaurs) about 140 million years ago. There are now more than 9000 different birds alive in the world today, and about 750 species of bird in Australia.

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Amphibians:
These are animals that:
  • Are cold blooded and cannot keep their body temperature constant.
  • Generally have soft, moist skins, although toads have dry, warty skins.
Amphibians live partly in the water and partly on the land, and evolved from the fish about 380 million years ago. There more than 3000 species alive in the world today. They include frogs, toads, salamanders and newts. Frogs are the only native amphibians in Australia, and there are 180 different species. Most frog lay eggs in freshwater ponds. They hatch into tadpoles which look like small fish with fins and gills. When they are fully grown, tadpoles turn into frogs and move onto the land. Frogs breathe with lungs and have moist skin, so they usually stay in damp places. Some live in the desert, and when the waterholes dry out they hide in moist burrows until it rains.

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Mammals:
These are animals that:
  • Feed their young on milk
  • Have fir or hair to keep them warm.
  • Keep their body temperature constant.
  • Breathe air with lungs.
Most mammals live on the land, although some, like dolphins and dugongs, live in the sea. Some mammals burrow beneath the ground, some live in trees, and others, like bats, are able to fly. They platypus and echidna are the only mammals to lay eggs. They are called monotremes. Many Australian mammals, like kangaroos and possums, give birth to tiny, undeveloped young, which usually live in a pouch on the motherís belly. They are called marsupials. The other mammals give birth to fully formed young, and are known as eutherians. Mammals evolved from reptiles about 200 million years ago. There are 248 different mammals in Australia and around 4000 species in the whole world.

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1 September 2000