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Re: CROCODYLOMORPH ENDOTHERMY
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.
> 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.
Pacific Lutheran University
Tacoma, WA 98447
"If you can't convince them, confuse them." -- Harry S. Truman