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Re: Disney's Dinosaur Trailer




Patrick Norton wrote:

> My basic point is that evolution would be strongly selective towards
> minimizing mass in the distal forelimb elements of flying vertebrates, for
> obvious biomechanical reasons.

I agree wholeheartedly.

> So anytime we see isolated concentrations of
> mass in distal limb elements (such as avian wing muscles), we need to look
> for a very important functional explanation.

I fully agree about isolated concentrations of mass in distal limb elements, but
I wouldn't consider avian wing muscles to be an example, since in birds, most
distal limb elements are concentrated in the proximal part of the wing.  And in
birds, most of the wing muscles are inboard of the wrist, which isn't located
very far out on the wing..

>  We don't see such mass in bat
> wings (not much, anyway). We do see it in birds, but in my opinion--and this
> is what led to my original question-- the evolutionary rationale offered by
> researchers for maintaining that condition seems weak.

Try inertial and 'added mass' loads involved with wrist flexion and extension
during flapping.  Also, because of the disparity in the length of the moment
arms, even small drag forces require  large tensile loads in the muscle and
tendon that resists them.

Jim