Diprotodontia

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Diprotodontia[1]
Fossil range: Late Oligocene - Recent
A diprotodont, the Agile Wallaby (Macropus agilis)
A diprotodont, the Agile Wallaby (Macropus agilis)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Marsupialia
Order: Diprotodontia
Owen, 1866
Suborders

Vombatiformes
Phalangeriformes
Macropodiformes

Diprotodontia (Greek, means "two front teeth") is a large order of about 120 marsupial mammals including the kangaroos, wallabies, possums, koala, wombats, and many others. Extinct members include the rhinoceros-sized Diprotodon, and Thylacoleo, the so-called "marsupial lion".

Contents

[edit] Characteristics

Living diprotodonts are almost all herbivores as were most of the those that are now extinct. There are a few insectivores and omnivores, but these seem to be relatively recent adaptations from the mainstream herbivorous lifestyle. The extinct thylacoleonids ("marsupial lions") are the only known group to have exhibited carnivory on a large scale.

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 there is virtually no record at all in geologically active New Guinea; the great diversity of known Oligocene diprotodonts suggests that they began to diverge well beforehand.

Many of the largest and least athletic diprotodonts (along with a wide range of other Australian megafauna) 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, in particular fire.

There are two key anatomical features that, in combination, identify the diprotodonts. The first of these is that they are diprotodont (meaning "two front teeth"): 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 rodents 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 marsupials share it) and is usually explained as an adaptation to a climbing lifestyle. Many modern diprotodonts, however, are strictly terrestrial, and have extensive further adaptations to the feet to suit that lifestyle. This makes the history of the tree-kangaroos particularly convoluted: it appears that they had an arboreal 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.

[edit] Fossil record

The earliest known fossil of Diprotodontia dates back to the Late Oligocene (23.03mya-28.4mya). The earliest identifiable species is Hypsiprymnodon bartholomaii from the Early Miocene.[2]

[edit] Classification

Until recently there were only two suborders in Diprotodontia; Vombatiformes which encompassed the wombats and koala and Phalangerida which contained all other families. Kirsch et al. (1997) split the families into three suborders. In addition, the six Phalangeriformes families are split into two superfamilies.

Order DIPROTODONTIA

† means extinct family, genus or species.

[edit] References

  1. ^ Groves, Colin (16 November 2005). in Wilson, D. E., and Reeder, D. M. (eds): Mammal Species of the World, 3rd edition, Johns Hopkins University Press, 43-70. ISBN 0-801-88221-4. 
  2. ^ http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=66275&is_real_user=1
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  • The Taxonomicon
  • Mikko Haaramo
  • [1] Implications of a new species of the Oligo-Miocene kangaroo (Marsupialia: Macropodoidea) Nambaroo, from the Riversleigh World Heritage Area, Queensland, Australia
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Extant mammal orders by infraclass
Kingdom: Animalia · Phylum: Chordata · Subphylum: Vertebrata · (unranked): Amniota
Australosphenida
Metatheria
Eutheria