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