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Re: Cold or Hot?
We have assembled nine lines of evidence that even the ancestors of
dinosaurs were endotherms.
You can see a recent review of this in Nature:
This article stems from the following paper which has the full story
(email me is you want a PDF):
Seymour, R.S., C.L. Bennett-Stamper, S.D.Johnston, D.R. Carrier, and
G.C. Grigg. 2004. Evidence for endothermic ancestors of crocodiles at
the stem of archosaur evolution. Physiol. Biochem. Zool. 77: 1051-1067.
Seymour, R.S. 2004. Reply to Hillenius and Ruben. Physiol. Biochem.
Zool. 77: 1073-1075.
Of course there is a range of adaptations among animals in regard to
temperature regulation and energy use, but if one looks at the
distribution, there appear two adaptive peaks: one is a high-energy,
endothermic state and the other is a low-energy, ectothermic state.
Those animals in the middle are under a selective disadvantage. On one
hand, they cannot be as aerobically active as true endotherms and
therefore are poorer predators and better prey. On the other hand, they
would require more energy than true ectotherms to keep them in this
state. True, there are examples of species that survive in the middle,
but they do not seem to be common.
It is also clear that there will never be a concensus. As I said in the
second paper above, it is just a matter of looking at the evidence as a
whole and forming an opinion.
Phil Bigelow wrote:
> On Sun, 05 Jun 2005 17:14:57 -0400 Tyler Kerr <firstname.lastname@example.org>
> <<<Has this already been discussed?>>>
> Yeah, but a rehash of the topic isn't going to kill anybody. ;-)
> <<<The previous posts about dinosaurs being big reptiles
> reminded me. I'm just a sophomore high school student so I
> don't have much knowledge on the subject, but was it ever
> discovered if dinosaurs were ectotherms (like reptiles) or
> endotherms (like their avian counterparts)? I've never
> heard anything of that nature being discussed and it's
> been bugging me lately. Thanks in advance.>>>
> As far as I can tell from reading the more recent literature, there is
> still no consensus pro or con. Here is some of the evidence in favor of
> warm-blooded dinosaurs:
> 1) Evidence of feathers on some small-mass theropods. Perhaps all small
> mass theropods had feathers. Apparent loss of feathers in the adults of
> large theropods. This suggests that feathers were needed to retain heat
> in the smaller animals. Larger dinosaurs didn't need the extra
> insulation (just as elephants don't need a lot of hair).
> 2) Oxygen isotope analysis of _T. rex_ bones suggests that the
> extremities were kept at an elevated temperature, close to that of the
> body's core, suggesting that the animal was warm blooded (or had a
> thermoregulatory scheme somewhere between "cold blooded" and "warm
> 3) Predator/Prey ratios in dinosaurs are similar to mammals, which
> suggests that, pound for pound, a predatory dinosaur consumed more fuel
> than, say, a cold-blooded croc' does.
> 4) *Possible* evidence of a fossilized 4-chambered heart in a
> plant-eating dinosaur suggests that the animal had a circulatory system
> similar to warm blooded animals (some researchers claim that what was
> found inside that dinosaur wasn't a heart).
> 5) Rapid growth, resorption, and restructuring of dinosaur bone suggests
> that dinosaurs had a faster growth rate and a higher metabolism compared
> to modern cold blooded animals.
> 6) At least SOME dinosaurs are known to be warm blooded: Modern birds!
Roger S. Seymour
Environmental Biology (Darling Building D418)
School of Earth and Environmental Sciences
University of Adelaide
Adelaide, SA 5005, Australia