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Re: Let's fix those pterosaur hands!

I also agree with Chris on this issue. David: I think you are making it more complicated than it needs to be. Examination of the antebrachium and hand indicates, based on several characters, that the anterior compartment is facing in the cranial direction during flight. This happens to be the only orientation that makes the myology and osteology align, as there is no evidence of spiraling tendons in the distal antebrachium or hand. The fact that this makes extension movements wider than flexion movements, while perhaps a bit odd to us, is really of very little consequence, as is the fact that the forelimb in this pose is no longer "typical", per se, for a tetrapod. The only osteological shift in this case is that the radius has moved its position distally somewhat, due to its particular articulation with the syncarpals. Be careful using the human antebrachium as a guide - we undergo a substantial upper limb rotation during development that somewhat reorganizes our upper limb, including the relative positions of the anterior/posterior compartment borders.

I also would not worry too much about the flight scenarios - we don't have enough information right now to actually devise the selection events related to pterosaur flight origins, so I took Chris' scenario in this case as simply being a speculative experiment demonstrating that such a path could be imagined. If you have an alternative scenario that also fulfills the required trajectories, then that simply fulfills the thought experiment a second time. Personally, I am not inclined to presuppose any sort of specific scenario for flight origins in pterosaurs at this time.



Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
(443) 280-0181

On Sep 29, 2009, at 6:34 AM, David Peters wrote:

Thanks to Mike Habib, I finally got a chance to read Chris Bennett's paper on pterosaur myology, based on two large pterodactyloids, Anhanguera and Pteranodon.

Morphological evolution of the wing of pterosaurs:
myology and function  Zitteliana B 28 127 - 141

Yes, I have comments, but today they have nothing to do with myology. It's the architecture, the organization of the skeleton according to Bennett, that draws criticism....