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Re: Cold-blooded dinosaurs revisited



At 02:20 PM 4/18/99 WAT, Caleb Lewis wrote:
>In addition, James O. Farlow - 
>a 
>> paleontologist - is quoted as saying that dinsoaurs were cold-blooded, but 
>> that theropds were "as active as" warm-blooded animals
>
>
>    Please excuse my bluntness, but, how in heaven's name is this possible?
>

Well, Farlow can answer in more detail about what he was specifically
talking about on that occasion, but several people have suggested that
dinosaurs may have had high active metabolic rates, while at the same time
retain low *resting* metabolic rates (see Reid's dino physiology chapter in
_The Complete Dinosaur_).

You (like a lot of people, of course) seem to be conflating a lot of terms
together.  There is a difference between base and active metabolic rates,
between activity level and thermogenesis, and so forth.  There is a reason
that physiologists do NOT use the terms "warm-blooded" and "cold-blooded" in
primary scientific discourse: they are hopelessly outdated concepts and
attempt to combine things which are in part independant.

Instead, look at types of thermogenesis (endo- vs. ectothermy), basal
metabolic rate (tachy- vs. bradymetabolism), relationship between internal
body temperature and environment (homeo- vs poikilothermic), etc.  Put on
top of this ontogenetic changes, allometric effects, etc. and you have a
better idea of the diverstiy of thermal ecologies of animals.  It's not an
"all-or-nothing" proposition.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661