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Fw: ptero endothermy





 > The prolacertiform hypothesis works. Cladistically it works if you throw
away Longisquama. And Sharovipteryx. And Cosesaurus. And Langobardisaurus.
If all you have is Tanystropheus for an outgroup, it just barely holds out
over Lagosuchus
> and that little bipedal croc, Scleromochlus.

That could also mean that prolacertiformes are really very basal
ornithodirans (sensu Gauthier, 1986). Especially seeing that they are close
to the dinosauriform *Lagosuchus*.

>That's all been published. It explains virtually every mystery we have of
pterosaurs. If you have, or have ever heard of a better hypothesis, please
bring it to the >table. And yes there is new
> news around the corner.

There is one mystery that this theory doesn't explain. That is the possible
homology between pterosaur hair and dinosaurian protofeathers. Accoriding to
Czerkas & Ji, 2002a the "hair" on *Pterorhynchus wellnhoferi* is very
similar in structure to Prum's "Stage II" of feather evolution. Such
feathers/hair are also seen in some dinosaurs and even modern birds have
feathers in which the barbs branch from a single calmus. It is possible that
stage II developed in the common ancestor of both pterosaurs dinosaurs.
Things like sharovipteryx were gliding animals unrelated to pterosaurs that
were trying to be pterosaurs but their metabloism wasn't very high and
probably couldn't do muh more than glide. It would be a rather odd
coincidence if stage II feathers developed in pterosaurs and dinosaurs
separately.

> 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.

According to Witmer, Chatterjee, Franzosa & Rowe, 2003, pterosaurs were
porbably superior fliers in comparison to birds and I don't think a
crocodile-like metabolism would be sufficient enough.

> 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.

Pterosaur ancestors had feathers. *Sharovipteryx* was unrelated to the
ancestors of pterosaurs and was just 'trying to be a pterosaur.' According
to John Conway (http://www.pterus.net) pterosaurs has thick coats of hair
(ptero-feathers, as I will call them from now on) as well as fat for
insultaion (as well as aerodynamic streamlining) and this seems quite likely
after looking at photos of the holotype of *Jeholopterus*. Nowhere is such
integument seen except in full-fledged endotherms. A lot of what you have
interpreted as dorsal frills in many pterosaur specimens could really be
hair, fat and rotting flesh that was compressed and squeezed under
thespecimens into an unnatural position. Speaking of dorsal frills, I can't
imagine the numerous aerodynamic ahh... ramifications such a structure would
have on an animal. Thet's where Conway's theory comes in also. He says that
fat and a thick coat of hair would also help with aerodynamics in
steamlining the animal. Also, so far there are no and have been no animals
that have or had scales and also had self-powered flight. All animals with
scales that can go airborne are gliders. besides, most animals have a very
regular shape to them and I can't think of how such an irregularly-shaped
structure like the dorsal frill you reconstruct would evolve, especially in
a flying animal!


Whew! That had to be my longest post here to date!


-------------------------------------
Mike Hanson
Email: mhanson54@comcast.net
Website: http://www.archosauria.org
Dinosauricon Art Gallery: http://dino.lm.com/artists/display.php?name=mike