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Re: pterosaur femora sprawl
The most likely gait, as you'll see, is the only gait that permits
pterosaurs to easily change from quad to biped, to balance over the
toes, to open their wings and take off. Now, if they rebounded into
the air from some sort of momentary spring-loaded crouch that you are
envisioning, that I want to see.
I was more wondering what factors led you to choose that gait in the
first place, rather than the effects you would expect it to have.
Changing from biped to quad might be interesting or useful, but that
doesn't mean it must have been the gait that was used. And, as Jim
already pointed out, you have the order of launch reversed: flying
vertebrates leap first, then engage the wings (even if they launch
bipedally like birds). A gait that places more weight on the hind
limbs does not make launch any more efficient for pterosaurs, though it
doesn't really constrain them either - the quad takeoff still works
just fine (the animals just shift weight more noticeably onto the
forelimbs during the crouch and unload). The key here is that opening
the wings before leaving the ground isn't actually very helpful, so
being able to balance on the hindlimbs and open the wings is of limited
importance. That's not to say that pterosaurs were incapable of doing
so, but merely that it would be unrelated to launch ability. Might be
useful for sunning one's wings, though.
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181