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Re: Biped advantage



At 08:41 18/11/96 +1030, George Olshevsky wrote:
>In a message dated 96-11-16 03:06:02 EST, pwillis@ozemail.com.au (Paul
>Willis) writes:
>
><< Oops. _former_ tree dwellers? I think not. Tree kangaroos have secondarily
> adapted to life in the trees (and a pretty ungainly one at that). >>
>
>This is very interesting. Any idea as to how this notion became established?

I believe that you will find that it is the commonly accepted view on the
evolution of the genus Dendrolagus (tree kangaroos) which are, actually,
rather clumsy in trees and tend to escape danger by leaping out of them
(often from great heights) and bounding away on the ground.

Certainly tree kangaroos are not particularly primitive as kangaroos go -
certainly not in the same league as the entirely terrestrial musky
rat-kangaroo Hypsiprymnodon moschatus, which retains five toes on the
hindfoot, is quadrupedal and bounds rather than hops (a very unroolike roo;
I saw them several times during field work in northern Australia in 1972-73).

However, this has nothing to do with the fact that kangaroos as a group are
generally regarded as having descended from arboreal ancestors, on the
grounds that the kangaroo line appears to have been an offshoot of the
possums which are mostly arboreal today.  The tree kangaroos, however, are
not representative of these ancestors but are secondarily arboreal - and a
newly-discovered species in New Guinea appears to be terrestrial, but
derived from arboreal tree kangaroos, thus making it a terrestrial
descendent of arboreal descendants of terrestrial descendants of arboreal
ancestors!

And if that doesn't make you stop and think about what dinosaurs could have
done, well, I can't help you...
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net