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