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Re: pterosaur femora sprawl





> From: Mike Habib <habib@jhmi.edu>

> 
> It is certainly possible to make many pterosaurs balance on the  
> hindlimbs (or at least to reconstruct them that way).  However, the  
> quad tracks and structural evidence for quad movement (especially quad  
> launch) indicates that all four limbs contacted the ground, at least  
> during walking and/or take-off.

True. True. True. And as you've seen, but perhaps don't remember from my 
drawings in Munich, I show them all with fingers grazing the ground. 
> 
> Perhaps I should ask why you expect that pterosaurs should be  
> bipedal?  Essentially, it would seem that they can be poked and  
> prodded into either a biped or quadruped stance; 

Ah, but configured correctly, Mike, the bipedal stance_is_ the quadrupedal 
stance!!  You'll see in the movie.I can also send any genus you request.

but since we don't  
> have biped trackways for pterosaurs, and given that they were built to  
> take off using primarily the forelimbs (not to mention that the wings  
> maintained anatomy associated with also being a walking limb), I'm  
> still confused as to why a bipedal stance would be preferred.  

You're thinking too polarized. Nearly all pterosaurs could and probably did 
touch the ground with their forelimbs. That I've never argued. However, having 
bipedal ancestors, they developed elongated pelves, higher sacral counts, 
shorter torsos and non-terrestrial forelimbs secondarily employed on the ground 
and continuously employed on trees and mates. Why should such a quadruped have 
an elongated pelvis and a fused sacrum unless there were strong lever forces 
acting upon them? As additional evidence, as you know, the elongated pelvis was 
less necessary in certain ornithocheirids, such as Arthurdactylus. Heck, even 
the sacrum became unfused. Why? Because they were flying all the time, and when 
they weren't flying they were most definitely quadrupedal.

I may  
> have misunderstood you (quite likely) but it would seem, from the  
> above comments, that you are arguing for bipedal gaits in pterosaurs  
> because they could get into a position that balanced them bipedally.  
> I'm not recognizing, however, where the simple ability to balance in  
> that manner translates into the most likely gait.

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.

Best, David
> 
> 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