The reason Australia has such unique and unusual animals (and plants) is that it was isolated from the rest of the world for over 60 million years. Separated by vast oceans, Australian plants and animals evolved independently of those in other parts of the world.
This is why Australian native animals are so different from those found elsewhere in the world. About 90 percent of the mammals, 70 percent of the birds, 88 percent of the reptiles and 94 percent of the frogs, in Australia, are found nowhere else on earth.
Interestingly many Australian fauna fill similar niches in the local environment to animals elsewhere in the world. For example the echidna is an Australian anteater. The Tasmanian tiger (now extinct) was a marsupial wolf. The marsupial mole too behaves in a manner similar to moles found in other parts of the world. The existence of similar animals in different parts of the world is referred to as "Parallel Evolution".
Ever wondered what animals are really native to Australia? Generally speaking, it is any animal that has been in Australia before the arrival of humans. The reason this definition is the best is because animals such as the koala and emu have been in Australia for millions of years and are unquestionably native. The the dingo, on the other hand, which considered native by some, was only brought to Australia by humans about 5,000 years ago. Many other animals such as camels and rabbits were introduced by European settlers less than 200 years ago. These animals are definitely not native to Australia.
There are three types of mammals in Australia. These are monotremes, marsupials and placentals.
Monotremes first appeared between 145–99 million years ago and are the oldest type of Australian mammals. Two out of the five known species of monotremes in the world live in Australia. The echidna and platypus are two such animals found in Australia.
Marsupials appeared about 64-65 million years ago and are the second oldest type of mammal found in Australia. They occupy every niche of the Australian habitat and range from the large red kangaroo to marsupials smaller than a mouse.
Placental mammals are relatively recent arrivals to Australia. Bats were the first to arrive, getting here about 23 million years ago. Rodents arrived about 5-10 million years ago. These animals reached Australia by flying or hitching a ride on floating debris and crossing the oceans that separated Australian from Asia as Australia as it stated drifting slowly closer to Asia. These placental mammals make up a very small percentage of the total mammalian population. Humans introduced a number of animals. The dingo was the first of these, coming here about 5,000 years ago. Beginning in 1788 many types of placental mammals such as cattle, the fox and rabbit were brought to Australia.
Australia has many amphibians and reptiles found nowhere else in the world.
Lizards – There are over 700 species unique to Australia alone.
Snakes – Australia has 140 species of land snakes and 32 species of sea snakes. Of these about a 100 are poisonous snakes. The bite from about 12 of these can be fatal to humans. The taipan and red-bellied black snake are some such poisonous snake.
Frogs – Four families of native frogs numbering 230 species inhabit the continent. 135 of these are unique to Australia.
Crocodiles – Australia has two species of crocodile. The Saltwater crocodile is the world's largest and can weigh as much as 1,000 kilos and is known to attack humans. Fresh water crocodiles are much smaller and do not attack humans.
Turtles – There are 35 species of freshwater turtles. Six species of sea turtle also visit the coastlines.
Australia has 800 species of birds of these 350 are only found in Australasia.
Ratites such as the emu and cassowary, are large flightless birds similar to the ostrich. The Emu lives in the Australian Outback. And the critically endangered cassowary lives in the tropical rainforests of Australia.
Megapods such as the Mallee fowl, trace their ancestry as far back as Gondwanan time. These stocky birds look somewhat like chickens but they have small heads and large feet (that's why the name "megapod" meaning big-feet). These birds are usually found in forested areas.
Other birds such as Kookaburras are the world's largest kingfishers.
Until Europeans came to Australia in 1788, there were no hoofed animals (like horses, cattle, goats, deer etc.) in Australia. There were no apes or monkeys in Australia either.
Rats and mice were the only animals that the Europeans didn't bring intentionally. They arrived as stowaways on ships.
An introduced animal is any animal that didn't naturally exist in Australia and was "introduced" — that is, brought intentionally or unintentionally by humans.
The first animals to be introduced into Australia by humans was the dingo a wild Australian dog. It was brought here by Asian sea-farers over 5,000 years ago.
Other introduced animals were brought here for agricultural purposes (cattle and sheep), for transportation (camel and horse), for sport (rabbit and fox), for pleasure (myna bird and house sparrow) and for pest control (cane toad). Some of these creatures, such as the cane toad, have been disastrous to the Australian ecology.
According to the Australian Department of the Environment's Endangered Australian Animals List many Australian native animals are endangered and threatened with extinction. For example; even the cuddly koala is listed as vulnerable, the cassowary and night parrot are listed as endangered and the gouldian finch as critical.
Many species of Australian mega fauna became extinct after the arrival of the Aborigines, first humans to arrive in Australia.
Since the arrival of European settlers in 1788 Australia has lost numerous other native animals and plants. The Tasmanian tiger is a prominent example of a recently extinct Australian animal. The last died in captivity in 1936.