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Re: pterosaur femora sprawl
By "storyboarding", Dave, do you mean the process of what happened
in the course of the launch? Actually, I'd be interested in seeing
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.
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.
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205