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George Olshevsky wrote:

>The prehensile tail, which (at least in _Drepanosaurus_, a close relative of
>_Megalancosaurus_ from the same locality, even has a specialized hook at the
>tip), makes it a good tree-dweller. This is all we need of the ancestral bird
>at this point in avian evolution.

Say what?  You mean any old thing in a tree is a potential protobird?  I am
glad to see you describe it as a side branch further down!

>If arboreal animals cannot develop an erect posture, then just how >did<
>monkeys do it? Ditto kangaroos, whose present-day smaller, arboreal relatives
>are pretty much erect.

First of all, I think it is a bit of a reach to say monkeys have erect
posture (any more than do, say, squirrels).  They  are definitely
quadrupedal.  As for kangaroos, tree kangaroos also get around pretty much
quadrupedally in trees and are regarded as secondarily arboreal in any case;
the most primitive living kangaroo, Hypsiprymnodon moschatus, is a
terestrial quadruped that doesn't even hop.

>Your comments about acquiring a fully erect gait address a point that I've
>been pondering for some time myself. One way to overcome this little
>difficulty is to suggest that dino-birds (like other thecodontians) were
>already semi-erect quadrupeds when they became arboreal.

And since maniratorian dinosaurs are already that way, suggesting birds
derived from proto-maniraptorians gets around it even better - especially if
they, too, were semi-arboreal.
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
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