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Re: Sifaka and Chukar Behavior: Trees Down or Ground Up?



Tim Williams (twilliams_alpha@hotmail.com) wrote:

<I agree and disagree at the same time.  I agree that use of the arms in 
aerial locomotion is irreconcilable with concomitant use of the arms in
prey seizure.  But, what if the forelimbs had become detached from 
grasping+holding predation by virtue of those lethal eumaniraptoran feet?>

  A while ago, I drew parallels to cats as a possible mechanism by which
the predatory stroke can be exampted in an arboreal animal with feathered
wings... I still see no problem with this. The difficulty here is the
relative adaptation to airfoils that while leaping and gliding, the feet
and arms had to have been engaged to some degree. In leaping, predatory
cats use only their arms in spread or extended fashion, whereas the legs,
with equal equipment, are extended behind and used only to stabilize a
landing. The cat does not bring its whole weight atop the surprised tapir
or bird, just the arms. If this model is applied to NGMC 91, it is easy to
see how it would work. One would not need any extra equipment, and the
legs would be held under, ready to engage. Problem is, the animal would
need its arms to slow its descent. A gliding adaptation such as in in
*Microraptor* would seem to force useage of the arms apart from predatory
striking, and the feet may not have been able to withstand the landing
forces; even though it is a small animal, the landing would be rather
rough, especially if its a struggling prey animal. Though I couldn't state
a certainty on this. No squirrel or colugo pounces on prey, and so am
extant gliding analogy is not known. The hindlegs are equally equipped for
induction of drag, and figuring out how they would be affected by a
forward set of claws during the famous "flying leap" is not known. The
restorations would suggest that the splayed leg, an apparent
impossibility, would have the concave surface on medial side, but I do not
think the fossils show which side, if any, is cambered, and this mya be
critical in evaluating use of legs, as previously stated, in the predatory
movements. It may not even used the legs during predation, and use the
gliding or incipient flight structure to get around only, and claws were
employed independantly.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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

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