Re: Thou Shalt Not Climb!

["Jaime A. Headden" <qilongia@yahoo.com>]

Kris Kripchak (mariusromanus@aol.com) wrote:

<Were basal birds up in the trees before they had the modern traits we now use
to define a bird as arboreal???  If yes, what were the traits that allowed them
to be there?  If not, then why did selection favor characteristics for an
arboreal lifestyle?>

  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. 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.

  So my answer would be that yes, these critters would have climbed before they
stayed up. Also, I suspect a great deal of small dinosaurs capable of climbing,
some more than others. Thus, multiple opportunities for true arboreality. I
suspect that theropodan skeletal pneumaticity gave it greater advantage than
did those ornithischians that seemed "tree-capable" in permitting ease of
climbing, and excercise in the trees was far more productive. Moreover,
predation in the trees would lead to advantage in climbing after difficult and
small prey, and this could leading to the "scampering" features that
*Archaeopteryx* displays, prior to the advent of selection for other dietary
niches (fruit, grubs, etc.) largely found among the branches.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


       
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