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Re: Thou Shalt Not Climb!

Jaime Headden wrote:

More than likely, the animals were in trees before the selective advantage
for arboreality became apparent. Not even *Archaeopteryx* is _arboreal_, though
it was certainly scansorial. All other basal birds, begining at least with
*Confuciusornis*, appear to be arboreal, with derived hindlimb for
branch-sitting (maybe not "perching" per se) and reduced forelimbs for
climbing, etc., while birds antecedent in anatomy seem to be a lot less
inclined to the trees.

Jaime, out of interest, could you (briefly) describe what anatomical features in the hindlimb distinguish "branch-sitting" from "perching".

Nearly all the long-tailed Liaoning birds have ropbust
hindlimbs and the "scampering" forelimb structure, leading one to suspect a
form of four-legged tree-climbing habitus with equal measures on the ground, in
the rocks, or in the trees, without any selective advantage (yet) for one or
the other.

Can you explain exactly what is meant by a "scampering forelimb"? In other words, what characters in the forelimb suggest that it was used for scampering? How are these forelimb characters different from characters associated with (say) predation?

BTW, I don't disagree with the idea that _Archaeopteryx_ and other basal avians could have (and did) climb up trees. I'm just intrigued as to how the anatomy of _Archaeopteryx_ supports this interpretation.



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