Re: Fw: [GSP1954@aol.com: MORE DINOSAUR ENERGETICS]

[Nick Longrich <longrich@stardot.com>]

[ FYI, Nick, I'm not planning to forward this message to Terry, so if
  you didn't already and you want him to see it it's up to you. -- MR ]

Terry Jones wrote:

> Once again, there is NO direct evidence of endothermy in dinosaurs!!! 

        Once again, Jones is most likely wrong. Although he may have seen 
photos, I am pretty sure he must not have seen the photos I have seen of 
the Chinese feathered dinosaur. They were very detailed, close-up 
photographs. They show insulatory structures, clearly. Could be fur, for 
all I know, but they are insulatory structures, not scales or a 
lizard-like crest. Anyone who has seen the photos shown to Ostrom can see 
this for themselves, it does not require any expertise or paleontological 
training to see that this is what they are.   

> There is an easy way to decide for yourself...
> 
> List all features of modern birds and mammals that are directly linked
> (i.e., functionally and causally linked) to endothermy (therefore this
> list could not include: ilium length, posture, etc).  This list may
> include: insulation (not just flight feathers, but real insulation),
> four-chambered heart (not functionally four-chambered as in crocs),
> high respiratory surface area: lung vol., high resting rates of O2
> consumption, high lung ventilation rates, (if I were doing it, as we
> did when we started looking at this question long ago, I would include
> RTs and large nasal passage diameter)...You decide what should be
> included (just be sure that they are causally linked to endothermy--
> required for endothermy).  Do the same for ectothermy.  Once the list
> is complete see which of these there is evidence for in dinosaurs.  I
> am confident that none of the things in your endotherm list will you
> be able to find evidence for in dinosaurs.

        As for direct, functional links:
a) I do not see why evidence of endothermy must necessarily be direct. 
b) such evidence does exist. The argument I have heard is that upright 
posture evolved to limit lateral flexion of the spine and so allow 
breathing and moving simultaneously, and therefore the high rates of 
aerobic activity seen in modern endotherms. This could be wrong, and yes, 
sprawling endotherms- monotremes which have lower body temperatures than 
eutherians- do exist. Also note the squirrels (squirrels move in a 
bounding gait, however, which prevents lateral flexion of the spine). 
There may also be mechanical factors as well- it seems to me that in 
smaller  mammals, there tends to be more sprawl.  Bats and some 
pterosaurs sprawl a lot too. I'm not aware of any upright-limbed 
ectotherms alive today, however. 
In addition, the saurischia and pterosauria are both *highly* pneumatic 
and these air-sacs may have served primarily to improve air-flow through 
the lungs, allowing very efficient breathing unlike what we see in 
reptiles, even in the mammals.  This means that high rates of lung 
ventilation very likely did exist. 
Also, pterosauria appear to have been insulated. Not to mention there is 
the question of whether cold-blooded powered fliers of this size could 
even exist.  Endothermy may be one of the requirements for powered flight 
of any significant duration in large animals. 
As for four-chambered hearts, as I understand things- correct me if I am 
wrong here- the crocodilian heart is not functionally four-chambered, but 
functionally three-chambered! I was under the impression that the 
four-chambered heart had been modified so that it opened into a 
three-chambered heart while diving, cutting out the pulmonary circuit and 
moving oxygenated blood to the rest of the body. What this means is that 
dinosaurs and pterosaurs would have had four-chambered hearts, unless 
birds and crocs evolved them independently.
        None of these argue exclusively for endothermy. But they are not 
explained by those who would argue for ectothermy.      Note also that 
while there are endotherms without RT, there are no ectotherms with 
insulation. So in a head-to-head between insulation and RTs, it may well 
be that insulation is a better indicator of endothermy. If the RT 
evidence is in fact as rock-solid as has been argued. I don't really know 
enough to judge on that.
        Nick L.