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Re: ptero endothermy



----- Original Message -----
From: "David Peters" <davidrpeters@earthlink.net>
To: <jrccea@bellsouth.net>; "dinosaur list" <dinosaur@usc.edu>
Sent: Thursday, January 29, 2004 7:05 AM
Subject: ptero endothermy


> Chris Bennett wrote:
> > Some interpret the presence of
> > that covering as evidence of bird-like and mammal-like endothermy;
> however,
> > that covering probably is better interpreted only as evidence that
> > pterosaurs were insulated to some extent and probably used that
> insulation
> > to "improve" their thermoregulatory capabilities over what they would
> be if
> > uninsulated.
>
> I agree with Chris.  I don't see any compelling evidence of endothermy
> in pterosaurs.  Nothing about their flight style requires it.  A
> crocodilian-like metabolism would probably suffice.  However, that
> doesn't mean that they were exothermic either.
>
> Jim
>
> >>>
>
> One of the reasons why pterosaurs were connected to dinosaurs for so
> long was the morphology of the pelvis. In both the anterior process of
> the ilium can be quite substantial. Greg Paul is better acquainted with
> this than I, but one can see that the early dinosaurs (theropods, and
> prosauropods) had rather small ilia while later forms had extended ilia.
> Longer ilia means larger thigh muscles.

Unless David knows about some pterosaur mummies that I am unaware of, I
would reject his suggestion that "longer ilia means [sic] larger thigh
muscles."  We do not have any direct evidence as to the mass of the
musculature of the muscles, as has been often pointed out be people
reconstructing musculature based on bony processes and muscles scars and
those rejecting those reconstructions.  The elongation of the ilium is best
interpreted as changing the mechanical advantage of the muscles originating
from it, moving the origin further away from the center of joint motion (in
this case the acetabulum).  Immense muscles could originate from a small
area by way of a tendon and small muscles can have broad areas of origin.
The elongate ilia of most if not all pterodactyloids are expanded somewhat
presumbaly to provide more area for the origin of muscles, but the ilia of
basalmost pterosaurs are relatively narrow straight rods that simply suggest
changes in the mechanical advantage of muscles relative to their ancestors
with shorter ilia.

Chris


S. Christopher Bennett, Ph.D.
Assistant Professor of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT  06601
http://www.bridgeport.edu/~cbennett

"Savor the sun--but when the clouds come make animals"  (Hexum)








> Big thigh muscles are used
> aerobically in dinosaurs -- burning more oxygen, which creates heat,
> yada yada. Endothermy. (How bad did I botch that scenario?)
>
> Pterosaurs had big ilia and big thighs before they had wings (and before
> dinos had big ilia). Look  at Cosesaurus, Sharovipteryx and now
> Longisquama. All big ilia and big thighs. If you want to draw
> conclusions you might speculate from the length of the ilia alone that
> whatever dinos were doing with their big thighs, pteros did first. But
> was it endothermy?
>
> Unfortunately, some are saying (as in the recent Sci Am) that even T rex
> might not have been an endotherm.
>
> So, let the arguments fly.
>
> About the pelage, well, Sharovipteryx had scales and big thighs, so the
> two don't necessarily go hand in hand. Sordes had hair. But was it
> enough for insulation? Not sure how, when or why hair appeared sometime
> during the Jurassic.
>
> David Peters
> St. Louis