[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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



-----Original Message-----
From: Scott Hartman <scott_hartman@hotmail.com>
To: larryf@capital.net <larryf@capital.net>; luisrey@ndirect.co.uk
<luisrey@ndirect.co.uk>; gigi.babcock@alumni.usc.edu
<gigi.babcock@alumni.usc.edu>; dinosaur@usc.edu <dinosaur@usc.edu>
Date: Sunday, December 10, 2000 5:48 PM
Subject: 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.


Yes, I should not have made such a general statement. The pelvic girdle of a
theropod would require some evolving in a different direction (different
enviornment). I was initially reffering to a more acute angle to the head of
the femur. Although  pterosaurs don`t come close to the near 90 degrees in
true theropods, I thought Dimorphodon closer to the more acute end of the
120-160 degree range. But then, upon looking into the matter further, I see
that Pterodactylus also posses a somewhat acute angle, so I guess my broad
statement about "early" pterosaurs is somewhat flawed. (There is an
interesting diagram in "The Arboreal Leaping Theory of Pterosaur
Flight"...Bennett, however, that shows a good degree of parasagittal motion
that Eudimorphodon was capable of).

>>>>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`m afraid I`m just an "armchair paleontologist" at this moment in time. I
read other peoples data and then try to interpret it the best I can. There
is much data relating these species to both dinosaurs and pterosaurs.
Padian, Benton and Sereno are good sources. Although I do trust cladograms
as valid statistical determinants of closeness of relationship, I don`t
think they necessarilly point out the "direction" of the evolutionary path.
I suspect, as you do, that pterosaurs evolved from the prolacertiform group
as Dave Peter`s probably makes clear in his recent paper on this subject (is
it out yet?).
That leaves me to interpret both Scleromochlus and Lagosuchus as being not
pterosaur ancestors, but secondarilly flightless descendants.

As for the "dinosaurian" as well as the pterosaur-like characteristics of
Lagosuchus, they seem to represent my idea that birds might have split off
from the pterosaur line.  In absence of a fossil pterosaur evolving flight
feathers, ...lagosuchians seem to be the only tangiable evidence I have of a
"missing-link" between these two groups.

If I had the ability to run a cladogram to investigate this possibility, I
would certainly do so!