"Reason"  wrote in message
news:...
> "Matt Lewis"  wrote in message 
> news:cj86nj$2tft$1{at}darwin.ediacara.org...
> > I've been wondering for a while about this and it seems that the main
> > advantage to maintaining a constant body temperature is that it allows
> > mammals and similar animals to maintain a high rate of cellular
> > respiration even in cold conditions.  This in turn allows the animal
> > to perform activities requiring lots of power, e.g. hunting, even in
> > very cold conditions.  However, animals such as sharks are apparently
> > able to produce high enough levels of power to hunt even in arctic
> > waters.  This seems to imply that they are able to respire rapidly
> > regardless of their internal temperature.  If this is the case, why
> > are mammals not able to perform the same trick and if they are why do
> > they waste energy maintaining body temperature?
> >
> > Thanks for any help,
> 
> 
> > Matt
> Possibly because during the long mesozoic era, when dinosaurs ruled most of 
> the earth, the mammals were only able to dominate the colder regions of the 
> globe, such as high elevations and polar regions.  To do this, they would 
> have had to be homeothermic (warm-blooded).

Or, more importantly, it allowed them to exploit the nocturnal niche
unavailable to the reptiles.
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