Re: Cold or Hot?

[Phil Bigelow <bigelowp@juno.com>]

On Sun, 05 Jun 2005 17:14:57 -0400 Tyler Kerr <tylerkerr@comcast.net>
writes:

<<<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
blooded").

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!


<pb>
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