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Physical characteristics diprotodontia

Diprotodontia > General of Diprotodontia

Diprotodont marsupials are united by two important characteristics that belie their great divergence in size and overall form. The first concerns dentition (the arrangement of teeth) in the lower jaw. Koalas, wombats, kangaroos, and possums all have only two developed incisor teeth at the front of the lower jaw.

The red kangaroo

These are large and often project forwards as an adaptation to cropping vegetation. A second pair of very small incisors is present in some species, but there are no lower canines, just a gap between the incisors and the cheek teeth. This arrangement is known as diprotodonty (literally translated this means “two first teeth”) hence the ordinal name Diprotodontia. The second major unifying characteristic of diprotodonts is syndactyly. This means “fused toes,” and refers to the structure of the hind feet, the second and third digits of which are always fused together forming a strange-looking double toe with two claws. The twin claws of the fused digits are retained and in most species serve the useful function of a grooming comb for removing caked dirt or other debris clinging to the animal’s fur.

Another shared feature of many diprotodonts is the arrangement of digits on the front paws. In most climbing species, the first two fingers oppose the other three, allowing the animals to maintain a firm grip of branches and stems. A notable exception to this rule is the brushtailed possum, whose forepaws are more like tiny nimble hands. Members of the suborder Vombatiformes are set apart from other diprotodonts, being rather squat and heavy, with a pouch the opens to the rear. In burrowing wombats this prevents the pouch filling up with soil, whereas in koalas it is a rather inconvenient arrangement inherited from non-climbing ancestors. Other diprotodonts, members of the suborder Phalangerida, have a more athletic build with a long tail.

In many possums the tail is prehensile. It may be thin as in potoroos or muscular as in large kangaroos, very long and brushy (as in Leadbeater’s possum, Gymnobelideus leadbeateri) or virtually naked. Phalangerids have retained the forward opening pouch of their ancestors as a secure means of transporting young while climbing or hopping. In members of the superfamily Macropodoidea (kangaroos, wallabies, and rat-kanga-roos), the hind legs are larger and more powerful than those at the front, and the hind feet are very long (the group and generic names macropod and Macropus mean “big footed”). In most macropods the first hind toe is absent.

Diprotodonts have soft fur-that of many possums and the koala is very woolly. The majority of species are some shade of gray or brown, but a few are rather dramatically colored-for example Goodfellow’s tree kangaroo (Dendrolagus goodfellowi), with a rich cinnamon red and gold coat and the yellow-footed rock wallaby (Petrogale xanthopus), whose yellow legs, feet, and ears, red and yellow-banded tail, and bold white cheek flashes contrast with gray body fur and make it one of the world’s more decorative mammals. Gliding possums are equipped with a built-in parachute, formed from a web of skin extending along each flank from the front to back legs. The precise structure of this membrane (called the patagium) varies between the three families of glider. In the pseudocheirid greater glider it stretches from elbow of the forelimb to ankle of the hind, while in the acrobatid pygmy glider it links wrist to knee. The lesser gliders (family Petauridae) have the most complete patagium, extending from wrist to ankle. None of the marsupial gliders have a tail membrane, although the tail of the pygmy glider is modified to assist the gliding process, with a vane of hairs along each side earning the species its alternative common name feathertail glider.

Convergent evolution is a recurring theme in marsupial history, and the diprotodonts are no exception. The diverse diprotodont body forms and lifestyles show striking similarities with mammals of several other orders. For example, the head of kangaroos is deer-like, with a long muzzle, erect, mobile ears and large bulging eyes situated on the side of the head. Like deer, kangaroos have good all-round hearing and vision and long, powerful legs capable of making dramatic leaps and propelling the animal at speed-all essential for avoiding predators in open habitats. The stout, badgerlike form of the wombats is an adaptation to burrowing, with strong legs, claws and jaws all contributing to the effort of excavating what can be very hard soils. With their woolly fur, round face, large, forward-facing eyes and careful climbing technique, the cuscuses are strongly reminiscent of primates such as lorises and pottos. The pygmy possums are the marsupial equivalent of European dormouse in looks and some aspects of behavior-they climb with the aid of a prehensile tail and enter deep hibernation in cold weather. The sugar glider (Petaurus breviceps) and Leadbeater’s possum resemble species of flying and non-flying squirrel respectively.

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