Re: Ornithodira, breathing with long necks

[MarkEShelly@aol.com]

In response to David Marjanovic, 

>>Several SVP abstracts of the last 3 meetings say that in many dinosaurs the 
>>energy costs of breathing surpassed the energy production of metabolism, 
>>means that those dinosaurs couldn't breathe, at least not through their 
>>nostrils, because of the dead space in the long trachea.<<

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?  

>>Respiratory turbinates or analogs? Are said to be a prerequisite for both 
>>homeo- and endothermy...< <  

Why? That feels more like a lawyer&#8217;s argument trying to argue a 
particular point of view. Why would a large animal (or even a small animal) in 
a warm, possibly moist climate need turbinates to recover heat or moisture?  If 
the outside air is warmer than the animal, evaporative cooling is about the 
only means of cooling available! (radiation, conduction, and conduction methods 
require a cooler environment or surface.)  Using moisture to cool the head 
seems more probable.  Turbinates are more likely (to me) heat retention 
improvements for animals whose endothermic ancestors spent some time in cooler 
climates as they vary.

<<At the SVP meeting 2000 it was proposed that sauropods held their necks stiff 
not with long, superstrong ligaments (no evidence for these can be found), but 
with air sacs between and in the vertebrae, just like birds do it. The abstract 
sounds very convincing.>>

Interesting!  At least it is a theory that could be tested.  How would they get 
pressurized?  Could they get enough pressure? Would it be possible with 2 air 
sacs?  Could they then bend the neck?   Of course, this use would preclude 
using them for breathing.

>>The air sac system is a synapomorphy of Ornithodira, and lung + air sac 
>>volume was big
enough to allow the evolution of 15-m-long tracheae. >>
 
Do you mean pre and post lung air sacs?  Do you mean post lung and neck air 
sacs. Was it big enough to allow endothermy.  

>>A large, powerful heart requires endo- and hom(o)eothermy.>>

Why?  Does it mean that they are required for the development of a 
four-chambered heart?  A large, powerful heart implies longer duration of 
effort to me, or a big body.  Why can&#8217;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?  As much as I want to believe 
all dinosaurs were endothermic like mammals, I can&#8217;t convince myself that 
it is the only explanation without answering these questions.

In response to > 5.  Freed hands due to the bipedal gait, with skin or 
feathers, would lead
to flight.>  
<<freed hands may facilitate the evolution of flight, even though bats never
were bipedal as far as is known... On the other hand, many bipedal animals
(kangoroos? humans? *Oreopithecus*?) have never evolved flight (but reasons
are easy to find here). For pterosaurs, the debate whether they had bi- or
quadrupedal ancestors continues (I favor the former).

Humans managed flight using machines made by their free hands&#8230; ground up 
according to the latest quarters (but not chasing after insects).
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.

    I would think this basil group would be the best place for endothermy and 
homeothermy
to start. 

In response to > Sauropods became so large that, except while young, a high 
metabolism
would not be needed (but may have occurred in the ancestral or youth stages).  
However, they would need exertion levels adequate to move to new feeding areas 
and for protection from theropods.> 

>>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. 

In his Predatory Dinosaurs of the World, he essentially stated that larger 
endothermic animals had lower metabolic rates per pound than smaller animals.  
Why would an extremely large animal generate lots of internal heat when he 
could not get rid of it?  It would just require more food. With a large 
stomach, crop, gizzard and stones, wouldn&#8217;t the breakdown of the food 
generate additional 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.
   Alternatively, a high metabolism better explains they large size and 
presumably rapid growth rate required to get there.