Re: Physiological Adaptations of the Dinosauria

["Tim Williams" <twilliams_alpha@hotmail.com>]

private private wrote:

> He [John Ostrom] hypothesized that the dinosaurs were endothermic (or
> warm-blooded) like their flying descendants. These two ideas became widely
> accepted over the next decade and a half until John Ruben, a physiologist
> working at the University of Oregon in 1996, scanned several dinosaur 
> skulls
> and showed that they lacked any trace of scroll-shaped bones (or 
> cartilages)
> in their nasal cavities known as respiratory turbinates.


Yes, but Mesozoic birds (including _Archaeopteryx_) lack RT's too - not 
surprising since they're usually made of cartilage and so unlikely to be 
preserved as fossils.  The absence of RT's in dinosaur specimens is 
therefore irrelevant to either to discussions on endothermy in dinosaurs or 
to the evolution of birds from dinosaurs

For an easily accessible, back-of-the-envelope rebuttal of the importance 
(or lack of importance) of RT's in endothermy and the origin of birds, by 
Greg Paul himself, check out:

http://www.cmnh.org/fun/dinosaur-archive/1995Sep/0187.html

> While this
> has the potential to solve many questions about the physiology of 
> dinosaurs,
> it may also explain their extinction. Since this system relies on ambient 
> air temperature being somewhat lower than the animal's core body
> temperature, it would likewise be drastically impaired by a global increase
> in temperature. Mammals, birds, and reptiles are oblivious to such factors.

This overlooks the oft-ignored fact that certain groups of birds, mammals 
and non-dinosaurian reptiles were also hit hard by the end-of-Cretaceous 
extinction.  Among birds, all except the neornithines went extinct (and the 
Cretaceous fossil record of this group is so meagre that it's possible their 
numbers plummeted too, only there were enough survivors to carry them across 
the K/T boundary).  Among mammals, as far as I know, only the placentals 
seemed immune to the K/T catastrophe.  Sea reptiles, pterosaurs and many 
crocodilians went extinct.  And that's just the vertebrates...


Tim

------------------------------------------------------------

Dr Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com