Re: Ornithodira, breathing with long necks

["Rob Gay" <rob_redwing@hotmail.com>]

> Does that mean they do not believe the neck air-sacs could act as an 
> alternate exhaust route to the trachea.  I do not know if any living 
> animals (most likely with long necks) have an alternate path.  Even if they 
> do not, why could in not be possible in Sauropods?<
As in, one path for exhaling, and the other for inhaling? It seems to me 
that it would be hard to take all the air inhaled through the nostrils down 
to the lungs before the lungs needed to exhale the waste gasses. It seems 
like the two would contradict each other, and you'd end with a dead 
sauropod. However, my understanding of respiration is limited, and so is my 
knowledge of sauropods. Maybe one of the sauropod guys or gals onlist could 
enlighten us.

> If the outside air is warmer than the animal, evaporative cooling is about 
> the only means of cooling available!<
This assumes that the outside air is indeed usually warmer than the animal. 
In endothermic homeotherms, the mean external temperature is a good deal 
cooler (usually) than the animal. Hence, we aren't sweating all the time.

> Using moisture to cool the head seems more probable.<
What of the rest of the body?

> Turbinates are more likely (to me) heat retention improvements for animals 
> whose endothermic ancestors spent some time in cooler climates as they 
> vary.<
But both the Permian and Triassic were characterized by very very limited 
ice caps at the south pole, and a vast desert in the interior of Pangea. 
There would be no real cooler climate for these animals to hang out it, from 
what I understand. The world was pretty hot and dry.


> How would they get pressurized?<
I'd assume through repiration. We are dealing with large lungs here.

> Could they bend the neck? Of course, this use would preclude using them for 
> breathing.<
I'd assume that by reducing the pressure in the sacs, through repiratory 
controls, the neck could vary in stiffness. I don't see how this precludes 
them for use in breathing. How else would the air get there, and pressure be 
regulated?

> Was it big enough to allow endothermy?<
The question is, do air-sacs always equal endothermy. And what is this 
threshold that you are talking about here?

> Why can?t efficient lungs, a 4 chamber heart, an upright gait, and warm 
> external air mean high, long duration activity levels and rapid growth 
> could not be achieved?<
I'm confused by this statement.

> As much as I want to believe all dinosaurs were endothermic like mammals, I 
> can?t convince myself that it is the only explanation without answering 
> these questions.<
While the evidence does seem to point towards endothermy, I don't think I 
would agree that it would be a mammalian style endothermy. Rather, if 
anything, it would be avian, or primative avian, where their resting 
temperature can drop a good deal.

> Humans managed flight using machines made by their free hands? ground up 
> according to the latest quarters (but not chasing after insects).<
But not biologically. And there has been no pressure selecting towards 
hominid flight, in any case.

> As for as pterosaurs.  If they had a bipedal gait, I would doubt it was 
> very good.  Otherwise, there would probably have been many later flightless 
> pterosaurs.<
Not really. Why would flightless pterosaurs evolve, when most to all niches 
are filled on land by dinosaurs. The likely place for flightless pterosaurs 
would be islands, and the only place I can think of off the top of my head 
to find these fossils, would be California, where island terranes were being 
accreted onto the continent. Besides, why could their be quadrapedal 
flightless pterosaurs?

> > HP Gregory S. Paul is onlist, so if he hasn't already done this today (my 
> > mail server is overloaded), he will surely tear any argument that 
> > sauropods didn't need high metabolism to very, very small pieces.<<
Indeed. I find HP Paul's Dinofest paper most intriguing.

> In his Predatory Dinosaurs of the World, he essentially stated that larger 
> endothermic animals had lower metabolic rates per pound than smaller 
> animals.<
But, predatory dinosaurs were nowhere near the size of the largest 
sauropods. But, I'll let HP Paul fill in the details, since I believe he has 
a greater understanding of this than I do. But I too recomend his 1994 
Dinofest paper.

> Why would an extremely large animal generate lots of internal heat when he 
> could not get rid of it?<
Why couldn't it? With a large surface area, facilitated by etremely long 
legs, neck and tail, there was plenty of surface area to volume to dump 
excess heat.

> Sauropods may have been endothermic (I believe they were), I am just 
> looking for a reason why a large animal (or small for that matter), with a 
> 4 chambered heart, and birdlike lungs would have to have been endothermic 
> and homeothermic to be active or grow fast if his body was warm.<
It doesn't need to be. But, it is more likely, I think. Where is the 
evidence for the avian lungs and 4 chambered heart, though?
Peace,
Rob

Student of Geology
Northern Arizona University
P.O. Box 20840
Flagstaff, Az. 86011
AIM: TarryAGoat
"A _Coelophysis_ with feathers?"

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