Re: FOUR, THREE, TWO, ONE . . . PTEROSAURS HAVE LIFT OFF!

[Mike Habib <habib@jhmi.edu>]

David Peters wrote:

> I see arcs that must not intersect the ground. Pterosaurs had a huge  
> arc to pass, one way or the other, as they started with  hands on  
> the ground at the zero point on the graph. Granted, there ought to  
> be more bounce when quad, but is it enough?

If it isn't enough, then biped launching is going to be even worse.   
My calculations thus far indicate that quad launching gives plenty of  
clearance but biped launching does not.  I could be wrong, but I  
haven't seen any structural or kinematic data to indicate otherwise.   
Either way, ground clearance is certainly an important factor, and one  
that I watch for, as well.


> In the meantime, I always encourage nonbiped believers to go check  
> out this site with movies of treadmilling lizards -- none of which  
> are as good at this as basal pterosaurs were for a whole raft of  
> anatomical reasons. But dang they're fast. And with  that kind of  
> rocket-like speed, maybe launching was different than has been  
> imagined. With the hands off the ground, strange things can happen.

They are indeed fast.  Some quadrupedal lizards are even faster.   
Unlike pterosaurs, though, bipedal lizards (or rather, those that run  
bipedally) do not have extremely gracile hindlimbs and super-strong  
forelimbs.  This also goes back to the basic issue of leaping vs.  
running launches - namely, that running speed is probably much less of  
a factor here than leaping performance.  Sweet videos, though,  
regardless.
>

> Also, as in most things pterosaurian, we can't over-generalize. What  
> was good for one, may not have been good for another due to the wide  
> variations in plan and size.

True.  So far, quad launch seems to be the best fit for just about  
everything I've analyzed (which includes azhdarchids, ornithocheirids,  
pteranodontids, anurognathids, and tapejarids).  For anurognathids,  
both biped and quad launches work, but quad launch gives better  
performance, and there are a few forelimb traits that suggest it was  
the primary launch mode.  There is one species of mid-sized pterosaur  
that might have been an exception, but still working on that.  So,  
while generalizations are dangerous, I'd argue that a good starting  
point is helpful.  In this case, my argument is that starting with the  
position that most pterosaurs were quad launchers is probably the  
better option, at least at the moment.  We may then find some  
exceptions to the trend as time goes along (which would be nifty in  
and of itself).

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