For most of us, the most important thing to know about tree kangaroos is that they exist at all. I owe this knowledge to the cheating lying hypocrites of the US Creationist movement, which only goes to show that however hard you try to do evil, good may come of it. It turns out, perhaps surprisingly, that some of these fine individuals are capable of the arithmetic required to establish that two animals of every species now extant would not have fit into the floating box described in the Book of Genesis even if they were dehydrated, flattened and packed in like sardines, and therefore argue that there were fewer species back then: the varieties now extant developed from the ancestral pair as their descendants spread out across the Earth from their landing point on Mount Ararat. And one of the examples given in whichever now-forgotten source I read about this was that kangaroos, wallabies and tree kangaroos are all supposedly descended from the two lucky macropods that Noah rescued from the flood.

There may have been more argument and examples after the mention of tree kangaroos, but obviously I never got around to reading it: Imagine a kangaroo. Now imagine a tree. Now imagine the one in the other. Unless either (1) you are an alien from a planet with low surface gravity and tree-like growths that are very unlike trees, or (2) there is something seriously wrong with your imagination, you are now acutely aware that more research is necessary.

Tree kangaroos are thought to have evolved from ground-living animals much like kangaroos and wallabies. Exactly why such well-adapted plains-dwellers should have started climbing trees is not clear, but they may have simply had nowhere else to go and ended up stuck in places where more trees started growing and those better able to exploit them had a better chance of survival. Those places now being New Guinea, Northern Queensland and a few of the islands around that corner of the Australasian ecozone. If you are surprised that there are kangaroos in New Guinea, you should not be: during the last ice age, when sea level was around 100 metres lower than it is now, you could have walked from Sorong to Hobart (although you would have had to build them first).

Then again, if we start bringing time-travel into things, there is no reason whatsoever to find tree kangaroos at all interesting or surprising: around 25 million years ago the ancestors of kangaroos were small arboreal creatures. They adapted to living on the ground as the trees died off. So the tree kangaroos have just returned to their more distant ancestors' habitat. They are smaller than gound-living kangaroos: being 40 to 80 centimetres long without the tail, plus as much again or more in tail, and weighing up to 14 or 15 kilogrammes. Their long tails help them balance, either by suitable waving in the air or by appropriate laying along a branch or tree trunk. The tail is not used for grasping. For hopefully obvious reasons they have stronger front legs than the kangaroos you first thought of.

Exactly how many species and sub-species there are of tree-kangaroos is not entirely clear and may depend on who you ask. According to Wilson and Reeder's Mammal Species of the World the species and subspecies of Dendrolagus can be classified as shown below along with their 'common' names and where they live, under the heading 'Boring Appendix' 'Taxonomy.' They all do and eat the things you might expect animals that live in trees to eat and do:

Tree kangaroos will eat more or less anything they can find up, down, in or out of a tree: leaves and fruit, obviously, bark, sap, flowers, seeds, insects and small birds. Their digestive system is similar that of non-tree kangaroos, with a chambered stomach capable of breaking down quite challenging fibrous material. Their teeth are rather different, reflecting the needs of their different diet.

Tree kangaroos climb and jump. Their back legs are still pretty powerful, which can be useful when climbing trees. Goodfellow's tree-kangaroos for example can hop up a tree trunk with their back legs while holding onto it with the front legs. The back legs also come in useful for leaping from tree to tree, which they have been observed doing over distances of 9 metres (that's 30 feet in the old money). Apart from that, at least some of them are quite good at getting out of trees quickly if they have to: Goodfellows can jump 9 metres and Matschie's tree kangaroos can jump 18 metres from a tree to the ground with no ill effects. (So why is there no tree-kangaroo-like superhero?)

Most tree kangaroos are near-threatened, vulnerable, endangered or critically endangered species, except for the merely rare and the extinct ones. They are under pressure from hunting and from habitat loss as people inexplicably continue to cut down trees for money or to build on the land. Being small and harmless and slow on the ground they have only one real asset in their fight for survival: they are preposterously cute. Only ignorance can explain the widespread absence of zoologically accurate tree-kangaroo soft toys in the bedrooms of Europe and North America. Why anti-logging campaigners have not already started to exploit their furry black-eyed beauty remains a mystery.

Taxonomy

http://www.zoo.org/animal-facts/treekangaroo
http://en.wikipedia.org/wiki/Kangaroo
http://en.wikipedia.org/wiki/Tree-kangaroo
http://eol.org/pages/34777/media

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