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

Jaime A. Headden" <qilongia@yahoo.com> wrote:

Sifakas lack any leg-gliding equipment, leaping aided almost wholly by a "halo" of body hair including some extra long underarm hair badly in need of trimming, inducing greater drag than in sleeker animals or other monkeys.

Feduccia went one step further, and suggested that the "brachial mat" (the long matted hair along the trailing edge of the arm) of the sifaka may constitute an airfoil.

So we now have two possible hypotheses for avian flight orgin, ground up supported by Ken Dial's experiments with galliforms, and trees down supported by Xu et al. on new (and not so new) fossils from the middle Cretaceous of Liaoning.

As others on this list have said, I'm not certain that one can claim that the two hypotheses are mutually exclusive. WAIR gets the creature up the tree, and the four wings gets it back down to the ground - in one piece.

WAIR also provides a functional explanation for the development of the wing stroke - or at least the co-option (exaptation) of the predatory stroke for a locomotory purpose. The matter of which came first in theropod evolution - the rudimentary flight stroke or the predatory stroke - depends on what phylogeny you favour.

An ambush predator cannot afford to maximize predatory equipment into a locomotory structure; [snip] animals that glide cannot simply switch to predatory mode while in flight, meaning that the wing structures are independant of predation.

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?


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