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Re: bipedality in pterosaurs (was:climbing dromaeosaurs and friends)



Larry,

Well, you raise some good questions, although they delve further into pterosaur anatomy than I'd intended to go. But here goes:

Certainly, the late Jurassic pterosaurs found in the Solnhofen limestone represent a good deal of evolutionary development and specialization of the pterosaur form. It is my opinion that the earlier pterosaurs of the Triassic might more closely resemble the basic theropod form.<<<

Maybe, but I doubt it. Sharovipteryx doesn't look particularily theropod-like. I'm not convinced that pterosaurs aren't related to prolacertiforms, like Dave Peters thinks (see: http://home.stlnet.com/~azero/Pterosaur_Homepage.htm for details). Even if pterosaurs are fairly close to basal dinosaurs, they don't seem to have any of the same pelvic girdle adaptations that theropods have for bipedal cursoriality. This doesn't mean that they couldn't have been bipedal, but if so, they did it in a different way.


From what I`ve read, I gather that Padian sees all pterosaurs as being capable of bipedal locomotion, whereas Unwin declares them all to be quadrupedal on the ground. I myself would compromise by saying that Dimorphodon and other earlier pterosaurs were capable of bipedal locomotion, and that later forms lost this capability.<<<

I'm not sure what Kevin Padian thinks about pterosaurs now. He certainly has been a staunch supporter of bipedal pterosaurs inthe past, but at the Denver or Snowbird SVP (I forget which now) he seemed to be softening to a position similar to yours. I actually think the situation is more complex. I susect that the antecedant of pterosaurs was arboreal, and probably a quadreped. There is evidence though, that many Dimorphodonts did indeed evolve some form of bidpedal locomotion, although I'm sure they were faculative quadrapeds.
Certainly Pterodactylus and Ptenochasma appear to have been true quadrapeds, and the Tate Museum houses a large collection of tracks that are extremely well preserved tracks that are almost certainly pterosaur in origin, and they are all quadrapedal. Despite this, derived pterosaurs (e.g. Quetzacoatlus) _may_ have evolved s faulative bipedality. So who knows, eh? Hopefully we'll soon see what Cliff and friends have to say on Quetzy and friends.


I'll tell you one thing I know for sure; it would sure be nice to find more three dimensionally preserved pterosaurs.

If one considers BCF, there exist many examples of secondarily flightless theropods from the Triassic right on through to present time. One might expect the same for pterosaurs, however, I can only see a couple of candidates for secondarily flightless pterosaurs ...Scleromochlus and Lagosuchus, both Triassic. Perhaps the lack of others beyond the Triassic reflects the loss of bipedal ability in the later pterosaurs.<<<

While the BCF is certainly worth considering, until more and better specimens are found from the appropriate strata, I have a hard time considering it the most likely hypothesis. Of course, I have my own ideas on how birds evolved... Either way I think Lagosuchus is more repsresentative of a dinosaur ancestor than a secondarily flightless pterosaur. Schleromochlus as a grounded pterosaur is certainly an interesting idea. If you haven't already, I recomend doing a phylogenetic analysis to see which characters support your hypothesis. If you have, I'd love to see it.
I will say this, that while terretrial cursoriality has evolved numerous times in the avian linneage, neither pterosaurs not bats have ever evolved into cursors. I suspect that this partially reflects differences in their origins, specifically bipedal cursor vs. arboreal quadraped.


Scott
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