Mammals of Australia

The mammals of Australia have a rich fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, but also including monotremes and placentals. 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 mammalian predators in Australia, the Tasmanian tiger and the marsupual lion, bore a striking resemblance to large canids such as the gray wolf and large cats respectively; gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle; and the numbat and anteaters are both digging insectivores. Most of Australia's mammals are herbivores or omnivores. The mammals of Australia have a rich fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, but also including monotremes and placentals. 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 mammalian predators in Australia, the Tasmanian tiger and the marsupual lion, bore a striking resemblance to large canids such as the gray wolf and large cats respectively; gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle; and the numbat and anteaters are both digging insectivores. Most of Australia's mammals are herbivores or omnivores. The fossil record shows that monotremes have been present in Australia since the Early Cretaceous 145 to 99 million years ago (mya). Marsupials probably existed in Australia at least from the early Paleocene (64 to 65 mya), although the earliest found undoubted fossils of Australian marsupials are from the late Oligocene 25 mya. The indisputable remains of Australian placental mammals started from the Miocene, when Australia moved closer to Indonesia. After 15 mya bats appeared reliably in the fossil record, and after 5 to 10 mya rodents did. The subsequent introductions of placental mammals into Australian fauna were about 1 mya (rats), several thousand years ago (dingo), and 200 years ago (many species); the last two were made by humans. Some claims were made about placental mammal fossils from the Eocene of Australia, called Tingamarra. These claims are based on only one found tooth having some characteristic features of condylarth, and were discussed widely. But both the age and placental nature of these fossils were challenged by other researchers. Monotremes are mammals with a unique method of reproduction: they lay eggs instead of giving birth to live young. Two of the five known living species of monotreme occur in Australia: the platypus and the short-beaked echidna. The platypus — a venomous, egg-laying, duck-billed, amphibious mammal — is one of the strangest creatures in the animal kingdom. When a platypus pelt was first presented by Joseph Banks to English naturalists in the late 18th century, they were convinced it must be a cleverly created hoax. Another strange monotreme is the short-beaked echidna; covered in hairy spikes, with a tubular snout in the place of a mouth, it has a tongue that can move in and out of the snout about 100 times per minute to capture termites. Australia is also home to the world's largest and most diverse selection of marsupials: mammals with a pouch in which they rear their young. The marsupial carnivores — order Dasyuromorphia — are represented by two surviving families: the Dasyuridae with 51 members, and the Myrmecobiidae with the numbat as its sole surviving member. The thylacine, or Tasmanian tiger, was the largest Dasyuromorphia and the last living specimen of the family Thylacinidae; however, 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 hunts although it is opportunistic. 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 grams (3 1⁄2 oz). There are two species of marsupial mole — order Notoryctemorphia — that inhabit the deserts of Western Australia. These rare, blind, earless carnivores spend most of their time underground; little is known about them. The marsupial omnivores include the bandicoots and bilbies, order Peramelemorphia. 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, but they share characteristics from both carnivorous and herbivorous marsupials.