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Re: Warm- vs. Cold-blooded Dinos

>From: wraddatz@wheel.dcn.davis.ca.us (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).

swf@elsegundoca.attgis.com              sarima@netcom.com

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