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Re: Warm- vs. Cold-blooded Dinos
>From: email@example.com (Warren Raddatz)
> >5. Growth Rings: ...
> Wasen't there recently some new work done on this which showed
> growth rings in dinosaurs thought to be endothermic?
Yes - in fact growth rings have now been found in *most* dinosaur
However, I am not entirely convinced that this indicated ectothermy.
All it *really* indicates is seasonal growth rates in sub-adults
(and adults??). I think some sort of cool season torpor - akin to
hibernation - might cause this, even in otherwise homeothermic
And yes, "warm-blooded" and "cold-blooded" are an imprecise terms.
More precise are terms like:
homeothermic: maintaining relatively constant body temperature.
poikilothermic: body temperature varying with outside tempersture.
endothermic: regulating body temperature using internal metabolic heat.
ectothermic: regulating body temperature using external sources.
Almost all endothemrs are also homeotherms. The main exception is that
a few small forms show a shift to poikilothermy during hibernation.
(for instance, I have this is true of bats).
But even many ectotherms are *effectively* homeotherms. In actual
practice, most lizards maintain a much more constant body temperature
than one might expect. It is only under artificial conditions, in
the laboratory, that they become really poikilothermic. (Actually,
lizards *do* drop into cold torpor at night, but maintain a more or
less constant temperature all through the day).
The peace of God be with you.