Re: CROCODYLOMORPH ENDOTHERMY

[Dinogeorge@aol.com]

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.

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