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Diprotodontia is a large taxon of about 120 marsupial mammals including the kangaroos, wallabies, possums, Koala, wombats, and many others. Extinct members include the giant Diprotodon family, and Thylacoleo, the so-called "marsupial lion".

Diprotodonts are almost all herbivorous: there are a few insectivores and omnivores, but these seem to be relatively recent adaptations from the mainstream herbivorous mould.

Diprotodonts are restricted to Australasia. The earliest known fossils date to the late Oligocene. However it is certain that their genesis lies earlier than that: there are large gaps in Australia's fossil record and virtually no record at all in geologically active New GuineaNew Guinea located just north of Australia, is the world's second largest island having become separated from the Australian mainland when the area now known as the Torres Strait flooded around 5000 BC. The name Papua also refers to the island in whole or; the great diversity of known Oligocene diprotodonts suggests that they began to diverge from one well beforehand.

Many of the largest and least atheletic diprotodonts (along with a wide range of other Australian megafaunaThe large animals of any particular area or time are its megafauna . Generally a "large animal" is considered to be one weighing over 100 pounds (45 kg). Aside from its general and more strictly correct meaning, the term is often used as a shorthand way o) became extinct when humans first arrived in Australia about 50,000 years ago, possibly as a direct result of hunting, but more probably as a result of widespread habitat changes brought about by human activity, fire in particular.

A young Western Grey KangarooThe Western Grey Kangaroo Macropus fuliginosis is a large and very common macropod, found across almost the entire southern part of Australia, from just south of Shark Bay to coastal South Australia, western Victoria, and the entire Murray-Darling Basin i shows its diprotodont lower teeth

There are two key anatomical features that, in combination, identify the diprotodonts. The first of these is that they are diprotodont: they have a pair of large, procumbent incisors on the lower jaw. This is a common feature of many early groups of mammals and mammaliforms. The diprotodont jaw is short, usually with 3 pairs of upper incisors (wombats, like rodentMany, see text The order Rodentia is the most numerous of all the branches on the mammal family tree. Currently there are, depending on the authority consulted, between 2000 and 3000 species of rodent—roughly half of all mammal species. Rodents are founds have only one pair), and no lower canines.

Secondly, diprotodonts exhibit syndactyly: they have the second and third digits of the foot fused together up to the base of the claws, leaving the claws themselves separate. Digit 5 (the hallux) is usually absent, and digit 4 is often greatly enlarged.

Syndactyly is not a particularly common condition (though the Australian omnivorous marsupialsPeramelemorphia : Animalia : Chordata : Mammalia : Marsupialia Peramelemorphia Families: Peroryctidae Peramelidae The order Peramelemorphia includes the bandicoots and bilbies it equates approximately to the mainstream of marsupial omnivores . All members share it) and is usually explained as an adaptation to a climbing lifestyle. Many modern diprotodonts, however, are strictly terrrestrial, and have extensive further adaptations to the feet to suit that lifestyle. This makes the history of the tree kangarooAbout 9; see text. Tree kangaroos are macropods adapted for aboreal life. They are found only in the rainforests of New Guinea, far north-eastern Queensland, and nearby islands, usually in mountainous areas. It is understood that tree kangaroos evolved frs particularly convoluted: it appears that they had an aboreal lifestyle at some time in the far distant past, then became adapted to a terrestrial existence, developing their very long kangaroo feet, and finally returned to the trees once more, complete with a shortening and broadening of the hind feet and a novel climbing method.