Diprotodontia

The diprotodonts (Diprotodontia) are an order of Australidelfian marsupials that, without being one of the richest in terms of number of species, is one of the more striking for the diversity of those that make it up. From the imposing kangaroos (Macropus sp.) to the tiny pygmy phalangers (Cercartetus sp.) to the koala (Phascolarctos cinereus), the couscous (Phalanger sp.) or gliders (Petaurus sp.), the history of diprotodonts has been marked by an extraordinary capacity for adaptation, resulting in morphological diversity such as few other taxa show.

The order Diprotodontia is made up of marsupials with only two incisors in the jaw.

Features

The prominent central incisives of the mandible characteristic of the diprotodons are evident in this western grey kangaroo of the Isle of the Kangaroo (Macropus fuliginosus fuliginosus)

Living diprotodonts are almost all herbivores, as were most of those now extinct. Some insectivorous and omnivorous diprotodonts are known, and the Potoridae are almost unique among vertebrates in being largely fungivorous, but they seem to have emerged as relatively recent adaptations of the dominant herbivorous lifestyle. The extinct thylacoleonids ("marsupial lions") are the only group known to have been shown to be carnivorous on a large scale.

Diprotodonts are restricted to Australasia. The earliest known fossils date from the late Oligocene, but their genesis is certainly earlier, as there are large gaps in the Australian fossil record, and virtually no fossil record at all in geologically active New Guinea. The great diversity of known diprotodonts from the Oligocene suggests that the order began to diverge much earlier.

Many of the larger and less athletic diprotodonts (along with a wide range of other Australian megafauna) went extinct when humans arrived in Australia around 50,000 years ago. Their extinction possibly occurred as a direct result of hunting, but was more likely the result of widespread habitat changes caused by human activities, especially the use of fire.

Two key anatomical features, in combination, identify the Diprotodontia, although one of them is also shared with Peramelemorphia. The members of the order are, in the first place, "diprothodontics" (meaning "two front teeth"): They have a pair of large, procumbent incisors on the lower jaw, a common feature of many primitive groups of mammals and mammaliforms. The diprotodontic jaw is short, usually with three pairs of upper incisors (wombats, like rodents, have only one pair), and no lower canines. The second distinguishing feature of diprotodonts is 'syndactyly', a fusion of the second and third digits of the foot down to the base of the claws, which leaves the claws separated, giving them an odd, claw-like appearance. misshapen finger with two nails. The digit five is often absent, and the digit four is often greatly enlarged.

Syndactyly is not particularly common (although shared by Australian omnivorous marsupials) and is generally postulated as an adaptation to aid climbing. However, many modern diprotodonts are strictly terrestrial and have evolved other adaptations to their feet to better suit this lifestyle. This makes the history of tree-kangaroos especially complicated: it appears that the animals were tree-dwellers at some point in the distant past, then moved to the ground—gaining long, kangaroo-like legs in the process—before back to the trees, where they continued to develop a shortening and widening of the hind legs and a novel method of climbing.

Evolution

The oldest known fossil remains of diprotodonts date from the Oligocene (between 24 and 35 million years ago), although marsupials already existed in these lands since the Cretaceous.

Of the phylogenetic lines with species alive in our time, the oldest is that of the wombatids, which represent an approximation to what the first diprotodonts must have been, characterized in the living species by a short tail and the pouch open caudally.

Classification

Previously only two suborders were recognized, now three are recognized.

• Order Diprotodontia
  • Gender Brachalletes (extinct)
  • Gender Koalemas (extinct)
  • Gender Sthenomerus (extinct)
  • Gender Nimbadon (extinct)
  • Thylacoleonidae (extinct)
  • Palorchestidae Family (extint)
  • Wynyardiidae family (extint)
  • Suborden Vombatiformes
    • Family Phascolarctidae
    • Vombatidae Family
    • Ilariidae family (extint)
    • Diprotodontidae family (extint)
  • Suborden Phalangeriformes
    • Superfamily Phalangeroida
      • Family Phalangeridae
      • Family Burramyidae
    • Superfamily Petauroidea
      • Family Tarsipedidae
      • Family Petauridae
      • Pseudocheiridae
      • Acrobatidae family
  • Suborden Macropodiformes
    • Macropodidae Family
    • Family Potoroidae
    • Hypsiprymnodontidae
    • Ganguroo Family (extinct)
    • Galanary Family (extinct)