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Tree-kangaroos and friends (was Re: Bird reduce their "heating bills" in cold climates)

Dann Pigdon <dannj@alphalink.com.au> wrote:

> Neither do tree kangaroos, arboreal ant-eaters or arboreal
> foxes.

For tree-kangaroos, this is a myth.  Modern tree-kangaroos (_Dendrolagus_ spp.) 
have quite a number of arboreal characters which are lacking in fully 
terrestrial macropods.  In the words of Flannery et al. (1995): "Their 
morphology reflects this [arboreal] lifestyle, for all possess large and 
powerful forelimbs, and adaptations in the hindlimb which allow for extensive 
rotation of the foot."  The latter is also apparent in the giant fossil 
tree-kangaroo _Bohra_ (shortened tibia-fibular contact; open calcaneal-cuboid 
articulation).  Added to this, tree-kangaroos also tend to have wider hindfeet 
(pedes), and the claws on the manus and pes are very robust and recurved.

Tree-kangaroos are certainly not as specialized for arboreality as many other 
arboreal mammals (including other phalangeroid marsupials), but they are not as 
inept in the trees as is sometimes made out.  The same arboreal features 
evolved independently in the fossil macropod _Nambaroo_, a basal form 
(macropodoid) which still retains an opposable toe (lost in the ancestors of 
tree-kangaroos) and is interpreted as a decent climber (Kear et al., 2007).

As for the fully arboreal pygmy ant-eater _Cyclopes_: the hindfoot is actually 
highly specialized for arboreal (especially suspensory) behavior.  I won't go 
into details, but the pedal anatomy is outlined in Meldrum et al. (1997; Am. J. 
Phys. Anthropol. 103:85â102).  The tamandua (_Tamandua_), which spends time in 
trees as well as on the ground, shows a wide range of flexion of the 
metacarpo-phalangeal joint, consistent with branch-grasping.

I don't know about arboreal foxes.  But I'd be very surprised if they didn't 
have arboreal-related features that are absent from their terrestrial kin, even 
if it's just different intra- or intermembral ratios.

> Given how well hooved quadrupeds like goats can climb, I'd
> say that small ornithopods could easily 
> have had the necessary phys
l traits for the occasional
> (or even frequent) mad scramble up 
> something. I wouldn't expect anything particularly graceful
> - although lack of grace doesn't seem 
> to stop tree kangaroos doing their thing.
> Generally speaking it's easier to say what *is* arboreal
> than it is to say what *isn't*.

I disagree.  There are morphological correlates associated with climbing, and 
in the absence of such features it is best to assume that a fossil taxon is 
*not* arboreal.  I don't doubt that a small, desperate ornithopod could 
scramble up a tree.  But nothing about ornithopod anatomy suggests that they 
did this habitually, or even frequently.

I know goats and other hoofed mammals *can* climb; but they don't do it very 
often, and I would hardly call goats "arboreal".