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

["Scott Hartman" <scott_hartman@hotmail.com>]

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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