Re: pterosaur femora sprawl

[Mike Habib <habib@jhmi.edu>]

> 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