Re: CROCODYLOMORPH ENDOTHERMY

["Nicholas J. Pharris" <pharrinj@PLU.edu>]

On Fri, 26 Jan 1996 Dinogeorge@aol.com wrote:

> In a message dated 96-01-26 16:54:23 EST, pharrinj@PLU.edu (Nicholas J.
> Pharris) writes:
> 
> >I'm not talking phyletic arguments here.  I could easily say that 
> >warm-bloodedness started with the Ornithosuchia and therefore would not 
> >necessarily have anything at all to do with the Crurotarsi.
> 
> You can say anything you like, but there's no evidence that complete
> endothermy (or even any kind of endotermy) occurred as early as
> Ornithosuchia, which by the way is probably the sister-group to the
> crocodile-normal crurotarsans.

Sorry for the mixup.  I was talking about the clade Ornithosuchia 
(proposed to include Euparkeria, Ornithosuchidae, and Ornithodira).  Is 
this not widely accepted these days?

> >> How about bone histology of early crocs
> >> (sphenosuchians, etc.)? Any citable research there?
> >
> >You haven't been paying attention, have you, George?  Histological 
> >research is EXACTLY what I was asking for when this thread got started.  
> >If the long-legged, early crocs (sphenosuchians, _Protosuchus_, etc.) show 
> >fibro-lamellar bone, I will be more than happy to let this lie.
> 
> I get 300 e-mails a day. I'm supposed to remember the start of one thread
> that I'm not particularly interested in?

I apologize for the ad hominem jab.  But you have been contributing to 
this thread almost daily, and I have mentioned it before.  Again, I am 
willing to stake this whole thing on histology.  I know how far out on 
the limb I am here.
 
> I repeat: there is no reason to expect thecodontians to have been
> endothermic, and the fact that the one group of extant
> thecodontians--crocs--is basically ectothermic strongly suggests that the
> extinct thecodontians were ectothermic, too. 

No extinct non-croc thecodont sprawled like a croc or lived in the water, 
which dampens temp. fluctuations and lessens the need for endothermy.

> Erect posture suggests only that
> there was a circulatory system in which the pulmonary circulation was
> essentially separate from the systemic circulation, allowing higher blood
> presure in the limbs and body than in the lungs and allowing a higher level
> of exercise metabolism through better blood aeration. 

Which suggests endothermy.  At least in mammals, endothermy came first, 
then erect posture.

> Predator-prey ratios
> are virtually meaningless as far back as the Triassic; there are tremendous
> collection and preservational biases that confound any analysis. 

Proof?

Bone
> histology might make me sit up and take notice, but even that is
> questionable. We have a hard enough time convincing anyone of dinosaurian
> endothermy via bone histology, let alone of thecodontian endothermy, where
> the deck is really stacked against it.

Oh, really?  Excuse me, but I'm not so sure.

Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447
(206)535-8204
PharriNJ@PLU.edu

"If you can't convince them, confuse them." -- Harry S. Truman