re: pterosaur launching tactics

[David Peters <davidpeters@att.net>]

Mike and John [see addendum at the bottom of this letter],

and a copy [without images] to the dinosaur list:

I've attached lateral view images of four pterosaurs, each with its  
own proportional configuration problems/solutions in getting around  
terrestrially.

MPUM 6009, as you can see, retains the long legs of its ancestors,  
something all other pterosaurs lack. A pterosaur with such  
proportions would have about as much luck with a quadrupedal launch  
as a lemur.

Nyctosaurus and Arthurdactylus have such long wings proximal to the  
fingers that it's hard to see how they could _not_ move about  
quadrupedally. They look burdened by their wings. Any sort of launch  
would appear awkward and perhaps, goony.

On the other hand, Quetzalcoatlus, IMHO, seems well equipped for  
terrestrial locomotion, able to move about quadrupedally and to lift  
its wings readily. It also seems to have the best proportions in the  
hind limb and pelvis of the latter three to launch bipedally. In any  
case, among the pterodacs, the ability to extend the wings laterally  
while bipedal might have been sufficient to enable that first flap to  
get airborne (without hind limb assist), and thus they may have been,  
in a strict sense, launched by their forelimbs.

I might suggest that the relative brevity of the humerus in Q.  
provides less leverage for forelimb launch, but perhaps you guys  
don't rely strictly on this lever for your launch. Still, while I  
don't discount it, I'd like to see your version before guessing wrongly.

Anyway, this is the database from which I'm working. Interesting  
creatures. Answers don't come easy. All of us should work together to  
find consensus.

With regard to the vampire bat, Desmodus, despite its remarkable  
secondary abilities, phylogenetically, the muscularity and  
configuration of the hind limbs is so out of touch with any sort of  
standard tetrapod upright locomotion that there really is no hope for  
the hind limbs to assist in takeoff. In this case, they act more like  
the tail wheel of an airplane, keeping the butt off the ground. More  
importantly, please note that the fingers of Desmodus are beneath the  
humeral glenoid, the bat's center of gravity. The hindlimbs and its  
toes are far from it, which is not the case in pterosaurs, as you can  
see by the drawings. That's why in Desmodus the launch has to  
originate with the forelimbs.

***

Addendum: I do note that in Q., like Pterodactylus, in the bipedal/ 
quadrupedal configuration, the fingers are also below the center of  
gravity, the humeral glenoid. That is not the case with Nyctosaurus  
and Arthurdactylus. So what works for Q. and P. may not work for N.  
and A.

David Peters
davidpeters@att.net