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Re: pterosaur femora sprawl



By "storyboarding", Dave, do you mean the process of what happened when
in the course of the launch? Actually, I'd be interested in seeing this
myself - not being overly familiar with aerodynamics, I have to admit
that when I try to imagine it the ground keeps getting in the way. Where
am I getting confused?

I suspect that your confusion comes from trying to force the poor critter to deploy the wings too early (based simply on the fact that I get that bit of confusion a lot). A quad launching pterosaur would leap first, and then deploy the wings near the max height of the ballistic path. There is a tendency, I think, to expect that birds flap themselves into the air, and that being bipedal somehow makes ground clearance less difficult. Remember, though, that most living ground-launchers use a leap-first, flap-second kinematic, as it is.


Birds leap into the air with the hindlimbs, and only then do they deploy the wings. Only burst launchers, which have secondarily shortened wings, engage the wings early in the launch cycle, and even they still get most of the initial force for the launch from the hindlimbs alone (as much as 90% - see Earls, 2001). Vampire bats quad launch, and they also leap first, then deploy the wings. The difference, of course, is that the bat's forelimbs do 'double duty': after pushing off the ground, the forelimbs are in a position analogous to the end of a downstroke, so the bats simply upstroke quickly on the way up and then start in with the first downstroke as the top of the leap is reached. In fact, quad launching *reduces* the problems of clearing the ground, because the leap impulse is so much more powerful than a bipedal leap - it is birds that actually should have the most trouble clearing the ground.

Pterosaur quad launches would be very similar to vampire launches in many respects, though the launch angle would be much more shallow at large body sizes. I hope to have some images of pterosaur quad launch put together in the near future, which should help clear confusion.

Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280-0181 habib@jhmi.edu