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Re: Arboreal Dinosaurs



Bill Adlam wrote:
> 
> As for Hypsilophodon, this was originally reconstructed/restored with one toe
> pointing backwards, as in perching birds.  This led to the suggestion that it
> climbed trees.  That anatomical idea is now considered incorrect, and
> Hypsilophodon is not likely to be a climber (mainly because it's too big).

        There are smaller hypsilophodontids (like Leaellynasaura) which
could have conceivably been small enough to climb, although I agree
it was unlikely. Those forelimbs were pretty small, with short
stubby fingers.
        And here's where I (unashamedly) contradict myself.
        Although many arborial creatures have long arms and grasping
feet, these features are by no means essential. I believe the
original Hypsilophodon climbing model was based on the idea that
it superficially resembled a tree kangaroo. Tree kangaroos have the
normal macropod foot, with short (albeit muscular) forelimbs.
They are the only macropods that can move their hind limbs independantly
of each other (hopping forms move them together), although they
are also capable of hopping in the normal macropod fashion along
horizontal branches, which must require an incredible feat (feet?)
of balance.
        Saying this, I still think hypsies were probably not climbers.
One thing that would really clinch the idea of a particular species
being arborial would be a dino with tail vertebrae that suggest it
was prehensile. Australian possums mostly have squirrel-like tails,
although a few species (such as the ring tailed possums) have
prehensile tails. The same is true of many primate species, some have
them and some don't, so the absence of such a structure in most
dinosaurs does not immediately negate the idea.
        Does anyone know what vertebrae features distinguish
prehensile from non-prehensile tails? Do the prehensile forms have
a ball-and-socket structure like the vertebrae in snakes? Chameleon
scapulae have been compared to those of some dinosaurs, but what
about its tail?

-- 
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        Dann Pigdon
        Melbourne, Australia

        Dinosaur Reconstructions:
        http://www.geocities.com/capecanaveral/4459/
        Australian Dinosaurs:
        http://www.alphalink.com.au/~dannj
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