Fauna of Australia

The fauna of Australia consists of a large variety of animals; some 46% of birds, 69% of mammals, 94% of amphibians, and 93% of reptiles that inhabit the continent are endemic to it. This high level of endemism can be attributed to the continent's long geographic isolation, tectonic stability, and the effects of a unique 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 placental animals occupy elsewhere in the world. 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 between 48,000 and 70,000 years ago and by Europeans from 1788, has significantly affected 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. Based on the list of Australian animals extinct in the Holocene, about 33 mammals (27 from the mainland, including the thylacine), 24 birds (three from the mainland), one reptile, and three frog species or subspecies are strongly believed to have become extinct in Australia during the Holocene epoch. These figures exclude dubious taxa like the Roper River scrub robin (Drymodes superciliaris colcloughi) and possibly extinct taxa like the Christmas Island shrew (Crocidura trichura). Unsustainable land use still threatens the survival of many species. To target threats to the survival of its fauna, Australia has passed wide-ranging federal and state legislation and established numerous protected areas.

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 epoch 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 a rich mammalian fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, currently however there is limited taxonomic research into Australia's mammals. The fossil record shows that monotremes have been present in Australia since the Early Cretaceous 145–99 MYA, and that marsupials and placental mammals date from the Eocene 56–34 MYA, when modern mammals first appeared in the fossil record. Although terrestrial marsupials and placental mammals did coexist in Australia in the Eocene, only the marsupials have survived to the present. Non-volant placental mammals made their reappearance in Australia in the Miocene, when Australia moved closer to Indonesia, and rodents started to appear reliably in the Late Miocene fossil record. The marsupials evolved to fill specific ecological niches, and in many cases they are physically similar to the placental mammals in Eurasia and North America that occupy similar niches, a phenomenon known as convergent evolution. For example, the top predator in Australia, the thylacine, bore a striking resemblance to canids. Gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle; and the numbat and anteaters are both digging insectivores. For the most part, mammals are not a highly visible part of the faunal landscape, as most species are nocturnal and many arboreal.

Two of the five living species of monotreme occur in Australia: the platypus and the short-beaked echidna, the other three being echidnas that only occur in New Guinea. Monotremes differ from other mammals in their methods of reproduction; in particular, they lay eggs instead of giving birth to live young. The platypus — a venomous, egg-laying, duck-billed amphibious mammal — is considered to be one of the strangest creatures in the animal kingdom. When it was first presented by Joseph Banks to English naturalists, it was thought to be a hoax. The short-beaked echidna is covered in hairy spikes, with a tubular snout in the place of a mouth, and a tongue that can move in, and out of the snout at a rate of 100 times a minute to capture termites.

Australia has the world's largest, and most diverse range of marsupials. Marsupials are characterised by the presence of a pouch, in which they rear their young after birth. The carnivorous marsupials — Dasyuromorphia — are represented by two surviving families: the Dasyuridae with 51 members, and the Myrmecobiidae with the numbat as its sole extant species. The Tasmanian tiger was the largest Dasyuromorphia and the last living specimen of the family Thylacinidae died in captivity in 1936. The world's largest surviving carnivorous marsupial is the Tasmanian devil; it is the size of a small dog and can hunt, although it is mainly a scavenger. It became extinct on the mainland some 600 years ago, and is now found only in Tasmania. There are four species of quoll, or "native cat", all of which are threatened species. The eastern quoll for example is believed to have been extinct on the mainland since the 1960s, though there are efforts to reintroduce it. The remainder of the Dasyuridae are referred to as "marsupial mice"; most weigh less than 100 g. There are two species of marsupial mole — order Notoryctemorphia — that inhabit the deserts of Western Australia. These rare, blind and earless carnivorous creatures spend most of their time underground; little is known about them.

The bandicoots and bilbies — order Peramelemorphia — are marsupial omnivores. There are seven extant species in Australia, most of which are endangered. These small creatures share several characteristic physical features: a plump, arch-backed body with a long, delicately tapering snout, large upright ears, long, thin legs, and a thin tail. The evolutionary origin of this group is unclear, because they share characteristics from both carnivorous and herbivorous marsupials.