The fauna of Australia consists of a huge variety of unique animals; some 83% of mammals, 89% of reptiles, 90% of fish and insects and 93% of amphibians that inhabit the continent are endemic to Australia. This high level of endemism can be attributed to the continent's long geographic isolation, tectonic stability, and the effects of an unusual pattern of climate change on the soil and flora over geological time. A unique feature of Australia's fauna is the relative scarcity of native placental mammals. Consequently the marsupials, a group of mammals that raise their young in a pouch, including the macropods, possums and dasyuromorphs, occupy many of the ecological niches that elsewhere in the world are filled by placental mammals. Australia is home to two of the five known extant species of monotremes, and has numerous venomous species, which include the Platypus, spiders, scorpions, octopus, jellyfish, molluscs, stonefish, and stingrays. Uniquely, Australia has more venomous than non-venomous species of snakes.

The settlement of Australia by Indigenous Australians more than 40,000 years ago, and by Europeans from 1788, has had a significant impact on the fauna. Hunting, the introduction of non-native species, and land-management practices involving the modification or destruction of habitats have led to numerous extinctions. Some examples include the Paradise Parrot, Pig-footed Bandicoot and the Broad-faced Potoroo. Unsustainable land use continues to threaten the survival of many species. In recognition of the threats to the survival of its fauna, Australia has passed wide-ranging federal and state legislation and established numerous protected areas. However, many people believe that these measures fail to address the imminent threats to the survival of many species.

Both geologic and climatic events helped to make Australia's fauna unique. Australia was once part of the southern supercontinent Gondwana, which also included South America, Africa, India and Antarctica. Gondwana began to break up 140 million years ago (MYA); 50 MYA Australia separated from Antarctica, and was relatively isolated until the collision of the Indo-Australian Plate with Asia in the Miocene era 5.3 MYA. The establishment and evolution of the present-day fauna was apparently shaped by the unique climate and the geology of the continent. As Australia drifted, it was, to some extent, isolated from the effects of global climate change. The unique fauna that originated in Gondwana, such as the marsupials, survived and adapted in Australia.

After the Miocene, fauna of Asian origin were able to establish themselves in Australia. The Wallace Line—the hypothetical line separating the zoogeographical regions of Asia and Australasia—marks the tectonic boundary between the Eurasian and Indo-Australian plates. This continental boundary prevented the formation of land bridges and resulted in a distinct zoological distribution, with limited overlap, of most Asian and Australian fauna, with the exception of birds. Following the emergence of the circumpolar current in the mid-Oligocene era (some 15 MYA), the Australian climate became increasingly arid, giving rise to a diverse group of arid-specialised organisms, just as the wet tropical and seasonally wet areas gave rise to their own uniquely adapted species.

Australia has indigenous placental mammals from two orders: the bats, order Chiroptera, represented by six families, and the mice and rats, order Rodentia, family Muridae. Bats and rodents are relatively recent arrivals to Australia. Bats probably arrived from Asia, and they are present in the fossil record only from as recently as 15 MYA. Although 7% of the world's bats species live in Australia, there are only two endemic genera of bats. Rodents first arrived in Australia 5–10 MYA and underwent a wide radiation to produce the species collectively known as the "old endemic" rodents. The old endemics are represented by 14 extant genera. About a million years ago, the rat entered Australia from New Guinea and evolved into seven species of Rattus, collectively called the "new endemics."

Since human settlement, many placental mammals have been introduced to Australia and are now feral. The first was the Dingo; fossil evidence suggests that people from the north brought the Dingo to Australia about 5000 years ago. When Europeans settled Australia they intentionally released many species into the wild, including the Red Fox, Brown Hare, and the European Rabbit. Other domestic species have escaped and over time have produced wild populations including the cat, Fallow Deer, Red Deer, Sambar Deer, Rusa Deer, Chital, Hog Deer, Domestic Horse, Donkey, Pig, Domestic Goat, Water Buffalo, Blackbuck and the Dromedary. Only three species of Australia's nonindigenous placental mammals were not deliberately introduced: the House Mouse, Black Rat and the Brown Rat.

Forty-six marine mammals from the order Cetacea are found in Australian coastal waters, but since many of these species have a global distribution, some authors do not consider them Australian species. There are nine species of baleen whale, including the enormous Humpback Whale. There are 37 species of toothed whale, which include all six genera of the family Ziphiidae (Beaked whales), and 21 species of oceanic dolphin, including the Australian Snubfin Dolphin, a species first described in 2005. Some oceanic dolphins, such as the Orca, can be found in all waters around the continent; others, such as the Irrawaddy Dolphin, are confined to the warm northern waters. The Dugong (Order Sirenia) is an endangered marine species that inhabits the waters of northeastern and northwestern Australia, particularly the Torres Strait. It can grow up to 3 m long and weigh as much as 400 kg. The dugong is the only herbivorous marine mammal in Australia, feeding on sea grass in coastal areas. The destruction of sea grass beds is a threat to the survival of this species.

Ten species of seals and sea-lions (superfamily Pinnipedia) live off the southern Australian coast and in Sub-Antarctic Australian territories.

Australia has four families of native frogs and one introduced toad, the Cane Toad. In 1935 the Cane Toad was introduced to Australia in a failed attempt to control pests in sugarcane crops. It has since become a devastating pest, spreading across northern Australia. As well as competing with native insectivores for food, the Cane Toad produces a venom that is toxic to native fauna, as well as to humans. The Myobatrachidae, or southern frogs, are Australia's largest group of frogs, with 120 species from 21 genera. A notable member of this group is the colourful and endangered Corroboree Frog. The tree frogs, from family Hylidae, are common in high rainfall areas on the north and east coasts; there are 77 Australian species from three genera. The 18 species from two genera of the Microhylidae frogs are restricted to the rainforests; the smallest species, the Scanty Frog, is from this family. There is a single species from the world's dominant frog group, family Ranidae — the Australian Wood Frog — which only occurs in the Queensland rainforests. As elsewhere, there has been a precipitous decline in Australia's frog populations in recent years. Although the full reasons for the decline are uncertain, it can be at least partly attributed to the fatal amphibian fungal disease chytridiomycosis.

Australia has both saltwater and freshwater crocodiles. The Saltwater Crocodile, known colloquially as the "salty," is the largest living crocodile species; reaching up to 7 m and weighing up to 1000 kg, they can and do kill humans. They live on the coast and in the freshwater rivers and wetlands of northern Australia, and they are farmed for their meat and leather. Freshwater Crocodiles, found only in Northern Australia, are not considered dangerous to humans.

The Australian coast is visited by six species of sea turtle: the Flatback, Green Sea, Hawksbill, Olive Ridley, Loggerhead and the Leatherback Sea Turtles; all are protected in Australian waters. There are 29 species of Australian freshwater turtles from eight genera of family Chelidae. The Australasian Pig-Nose Turtle is the only Australian member of that family. Australia and Antarctica are the only continents without any living species of land tortoise.

Australia is the only continent where venomous snakes outnumber their non-venomous cousins. Australian snakes belong to seven families. Of these, the most venomous species, including the Fierce Snake, Eastern Brown Snake, Taipan and Eastern Tiger Snake are from the family Elapidae. Of the 200 species of elapid, 86 are found only in Australia. Thirty-three sea snakes from family Hydrophiidae inhabit Australia's northern waters; many are extremely venomous. Two species of sea snake from the Acrochordidae also occur in Australian waters. Australia has only 11 species from the world's most significant snake family Colubridae; none are endemic, and they are considered to be relatively recent arrivals from Asia. There are 15 species of boa, and 31 species of insectivorous blind snake.


There are more lizards in Australia than anywhere else in the world, with representatives of five families. There are 114 species in 18 genera of gecko found throughout the Australian continent. The Pygopodidae is a family of limbless lizards endemic to the Australian region; of the 34 species from eight genera, only one species does not occur in Australia. The Agamidae or Dragon lizards are represented by 66 species in 13 genera, including the Thorny Devil, Bearded Dragon and Frill-necked Lizard. There are 26 species of monitor lizard, family Varanidae, in Australia, where they are commonly known as goannas. The largest Australian monitor is the Perentie, which can reach up to 2 m in length. There are 389 species of skink from 38 genera, comprising about 50% of the total Australian lizard fauna; this group includes the blue-tongued lizards.

More than 4400 species of fish inhabit Australia's waterways; of these, 90% are endemic. However, due to the relative scarcity of freshwater waterways, Australia has only 170 species of freshwater fish. Two families of freshwater fish have ancient origins: the Arowana or "bony tongues," and the Queensland Lungfish. The Queensland Lungfish is the most primitive of the lungfish, having evolved before Australia separated from Gondwana. One of the smallest freshwater fish, peculiar to the south-west of Western Australia, is the Salamanderfish, which can survive desiccation in the dry season by burrowing into mud. Other families with a potentially Gondwanan origin include the Retropinnidae, Galaxiidae, Aplochitonidae and Percichthyidae. Apart from the ancient freshwater species, 70% of Australia's freshwater fish have affinities with tropical Indo-Pacific marine species that have adapted to freshwater. Nevertheless, fossil evidence indicates that many of these freshwater species are still ancient in origin. These species include freshwater lampreys, herrings, catfish, rainbowfish, and some 50 species of gudgeon, including the Sleepy Cod. Native freshwater game fish include the Barramundi, Murray Cod, and Golden Perch. Two species of endangered freshwater shark are found in the Northern Territory.

A number of exotic freshwater fish species, including Brown, Brook and Rainbow Trout, Atlantic and Chinook Salmon, Redfin Perch, Carp and Mosquitofish, have been introduced to Australian waterways. The Mosquitofish is a particularly aggressive species known for harassing and nipping the fins of other fish. It has been linked to declines and localised extinctions of a number of small native fish species. The introduced trout species have had serious negative impacts on a number of upland native fish species including Trout Cod, Macquarie perch and Galaxias species as well as other upland fauna such as the Spotted Tree Frog. The Carp is strongly implicated in the dramatic loss in waterweed, decline of small native fish species and permanently elevated levels of turbidity in the Murray-Darling Basin of southwest Australia.

Most of Australia's fish species are marine. Groups of interest include the Moray eels and squirrelfish, as well as the pipefish and seahorses, whose males incubate their partner's eggs in a specialised pouch. There are 80 species of grouper in Australian waters, including one of the world's biggest bony fish, the Giant Grouper, which can grow as large as 2.7 m and weigh up to 400 kg. The trevally, a group of 50 species of silver schooling fish, and the snappers are popular species for commercial fishing. The Great Barrier Reef supports a huge variety of small- and medium-sized reef fish, including the damselfish, butterflyfish, angelfish, gobies, cardinalfish, wrasse, triggerfish and surgeonfish. There are a number of venomous fish, among them several species of stonefish and pufferfish and the Red Lionfish, all of which have toxins that can kill humans. There are 11 venomous species of stingray, the largest of which is the Smooth Stingray. The barracudas are one of the reef's largest species. However, large reef fish should not be eaten for fear of ciguatera poisoning.

Sharks inhabit all the coastal waters and estuarine habitats of Australia’s coast. There are 166 species, including 30 species of requiem shark, 32 of catshark, six of wobbegong shark, and 40 of dogfish shark. There are three species from the family Heterodontidae: the Port Jackson shark, the Zebra Horn Shark and the Crested Horn Shark. In 2004, there were 12 unprovoked shark attacks in Australia, of which two were fatal. Only 3 species of shark pose a significant threat to humans: the Bull shark, the tiger shark and the Great White Shark. Some popular beaches in Queensland and New South Wales are protected by shark netting, a method that has reduced the population of both dangerous and harmless shark species through accidental entanglement. The overfishing of sharks has also significantly reduced shark numbers in Australian waters, and several species are now endangered. A megamouth shark was found on a Perth beach in 1988; very little is known about this species, but this discovery may indicate the presence of the species in Australian coastal waters.