Diprotodontia (Koala, wombats, possums, wallabies, and kangaroos) - mammals.worldmy.info

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Diprotodontia (Koala, wombats, possums, wallabies, and kangaroos)

Diprotodontia > General of Diprotodontia

The Australasian order Diprotodontia is not particularly large (it has just 131 described living species) but is one of the most startlingly diverse of all mammal groups. Its members include animals as superficially different as the teddybear-like koala (Phascolarctos cinereus), the tiny feather-tailed glider (Acrobates pygmaeus), and the magnificent red kangaroo (Macropus rufus).

A mother kangaroo holding her young

While some diprotodonts are instantly recognizable, others are rather obscure and they include among their number some of the world’s rarest animals. As a group, the diprotodonts are relatively new to science first recognized as an order less than 150 years ago in 1866. The earliest known diprotodont fossils date back to the Oligocene epoch 24–35 million years ago (mya), but even these constitute a diverse assemblage of forms, so the origins of the group almost certainly go back further, to the Cretaceous period. Then, like most early mammals, the ancestors of all Australasian marsupials were probably small insect-eating animals not unlike modern bandicoots (order Peramelemorphia) or the monito del monte (order Microbiotheria).

These ancestors arrived in Australia from South America and Antarctica when all three were united in the massive treecovered supercontinent of Gondwana. When Gondwana broke apart about 40 mya, Australia’s marsupials were isolated and began a major radiation. In the absence of large numbers of placental mammals, they expanded to fill a huge range of ecological niches. No group diversified more than the diprotodonts. There are currently 131 species of diprotodont in 40 genera, representing 10 families of koala, wombat, possum, cuscus, rat-kangaroo, kangaroo, wallaby, pygmy possum, ringtail, glider, honey possum, and feathertails. The suborder Vombatiformes, containing the living families Phascoloarctidae (koala) and Vombatidae (wombats) probably represents an early offshoot of the diprotodont lineage, characterized (at least in living members) by a reduced tail and backward-opening pouch.

All other diprotodonts are placed the same group, suborder Phalangerida, which represents the main trunk of the phylogenetic tree. This trunk splits into five major branches (superfamilies) of which two, the Phalangeroidea (possums and cuscuses) and the Burramyoidea (pygmy possums) contain just one family each. The other three superfamilies each unite two families, the kangaroos and rat-kangaroos in the Macropodoidea, the ringtails and gliders in the Petauroidea, and the honey possum and feathertails in the Tarsipedoidea. This classification is broadly supported by molecular data in which the sequences of certain key molecules including DNA are compared. The diprotodonts closest relatives in other orders are probably the bandicoots and bilbies (order Peramelemorphia) and the marsupial moles (order Notoryctemorphia). However these relationships are largely speculative.

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