Mammals

Australia has a rich mammalian fossil history, and a varied group of extant species dominated by the marsupials. The fossil record shows that monotremes have been present in Australia since the Early Cretaceous, and that marsupials and placental mammals date from the Eocene, 56–34 MYA, when modern mammals first appeared in the fossil record. Although marsupials and placental mammals did coexist in Australia in the Eocene, only marsupials have survived to the present. The placental mammals made their reappearance in Australia in the Miocene as Australia moved closer to Indonesia, and bats and rodents started to appear reliably in the fossil record. Marsupials evolved to fill similar niches and are in many cases physically similar to their placental counterparts in Eurasia and North America, which occupy similar ecological niches, in a phenomenon known as convergent evolution. For example, the top predator in Australia, the Tasmanian Tiger, bore a striking resemblance to canids such as the Gray Wolf; the Koala and the sloth are both arboreal herbivores; gliding possums and flying squirrels have similar adaptations to their arboreal lifestyle; and Numbats and anteaters are both digging insectivores.

Two of the four living species of monotreme occur in Australia: the Platypus and the Short-beaked Echidna. The monotremes differ from other mammals in their methods of reproduction; in particular, they lay eggs instead of giving birth to live young as do marsupials and placental mammals. The Platypus—a venomous, egg-laying, duck-billed, amphibious mammal—is considered to be one of the strangest creatures in the animal kingdom. The Bhort-beaked Echidna is similarly strange, 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 about 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. The carnivorous marsupials—order Dasyuromorphia—are probably the most similar group to the ancestral marsupials. The carnivorous mammals are represented by two surviving families, the Dasyuridae with 51 members, and the numbat as the sole surviving member of the Myrmecobiidae. The Tasmanian Tiger was the largest Dasyuromorphia and the last living specimen of the family Thylacinidae; however, what appears to have been the last known specimen 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 mainly eats carrion. 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 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 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.

Herbivorous marsupials are classified in the order Diprotodontia, and further into the suborders Vombatiformes and Phalangerida. The Vombatiformes include the Koala and the three species of wombat. One of Australia's best-known marsupials, the Koala is an arboreal species that feeds on the leaves of approximately 120 species of eucalyptus. Wombats, on the other hand, live on the ground and feed on grasses, sedges and roots. Wombats use their rodent-like front teeth and powerful claws to dig extensive burrow systems; they are mainly crepuscular and nocturnal.

The Phalangerida includes six families and 26 species of possum and three families with 51 species of macropod. The possums are a diverse group of arboreal marsupials and vary in size, from the Little Pygmy Possum, weighing just 7 g—to the cat-sized Common Ringtail and Brushtail possums. The Sugar and Squirrel Gliders are common species of gliding possum, found in the eucalypt forests of eastern Australia, while the Feathertail Glider is the smallest glider species.

The gliding possums have membranes called "patagiums" that extend from the fifth finger of their forelimb back to the first toe of their hind foot. These membranes, when outstretched, allow them to glide between trees.

The macropods are divided into three families: the Hypsiprymnodontidae with the Musky Rat-kangaroo as its only member; the Potoroidae, with 10 species; and the Macropodidae, with 40 species. Marcopods are found in all Australian environments except alpine areas. The Potoroidae include the bettongs, potaroos and rat-kangaroos, small species that make nests, and carry plant material with their tails. The Macropodiae include kangaroos, wallabies and associated species; size varies widely within this family. Most macropods have large hind legs and long narrow hind feet, with a distinctive arrangement of four toes, and powerfully muscled tails, which they use to move in a bipedal, energy-efficient hopping motion. The short front legs have five separate digits. The Musky Rat-kangaroo is the smallest macropod and the only species that is not bipedal, while the male Red Kangaroo is the largest, reaching a height of about 2 m and weighing up to 85 kg.

Placental mammals

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 are present in the fossil record only from as recently as 15 MYA, and probably arrived from Asia. There are only two endemic genera of bats, although 7% of the world's bats species live in Australia. 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. A million years ago, the rat entered Australia from New Guinea and evolved into seven species of Rattus, collectively called the 'new endemics'.

There are nine species of baleen whale present, including the enormous Humpback Whale. There are 37 species of toothed whale, which include all six genera of the family Ziphiidae 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 is an endangered marine species that inhabits the waters north eastern and north western Australia, particularly theTorres 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 seagrass in coastal areas. The destruction of seagrass beds is a threat to the survival of this species. Eleven species of seal—family Pinnipedia—live off the southern coast.