About 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 from creatures similar to modern kangaroos and wallabies, as they retain many of the standard macropod adaptations to plains life—notably the massive hind legs and long, narrow feet which, in more orthodox macropods, make fast, economical travel possible. Tree kangaroos, however, are slow and clumsy on the ground. Instead, they have developed exceptionally long tails for balance, and stronger forelimbs for climbing with. The feet are shorter and wider, they have longer claws on all feet, and rubbery soles for better grip.

The ancestors to all kangaroos were believed to have been small arboreal marsupials that look like some of Australia's present-day possums. The earliest macropods diverged from this line when they descended to the ground and evolved bodies adapted for rapid motion over the earth and rocks. Why ancestors of the tree kangaroos at some point turned around and returned to the trees is not known.

Though unable to move at much more than walking pace on the ground—hopping awkwardly with the body leaning far forward to balance the heavy tail—in trees they are bold and agile. They climb by wrapping the forelimbs around the trunk of a tree and hopping with the powerful hind legs, allowing the forelimbs to slide. They are expert leapers: 9 metre downward jumps from one tree to another have been recorded, and they have an extraordinary ability to jump to the ground from height without ill effect: 18 metres or more.

The main diet items are leaves and fruit, taken both in trees and on the ground. Other morsels are accepted when available, including grain, flowers, sap, bark, eggs and young birds. Their teeth are adapted for tearing leaves rather than cutting grass. They have large stomachs that function as fermentation vats where bacteria break down fibrous leaves and grasses. Similar to the stomachs of cows and other ruminant herbivores.

• Grizzled Tree-kangaroo (Dendrolagus inustus) northern and western New Guinea, plus Japen and Waigeo islands.
• Lumholtz's Tree-kangaroo (Dendrolagus lumholtzi), Queensland.
• Bennett's Tree-kangaroo (Dendrolagus bennettianus), Queensland.
• Huon Tree-kangaroo (Dendrolagus matschiei), eastern New Guinea.
• Goodfellow's Tree-kangaroo, (Drendrolagus goodfellowi), central New Guinea.
• Doria's Tree-kangaroo (Dendrolagus dorianus), far western, central, and southeastern New Guinea.
• Tenkile (Dendrolagus scottae), northern New Guinea.
• Lowlands Tree-kangaroo, (Dendrolagus spadix), lowlands New Guinea.
• Vogelkop Tree-kangaroo (Dendrolagus ursinus), western New Guinea.
• Dingiso, (Dendrolagus mbaiso), western New Guinea.

References

• Flannery, Timothy Fridtjof, et al. 1996. Tree Kangaroos: A Curious Natural History. Reed Books, Melbourne. ISBN 0-7301-0492-3