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Re: Warm- vs. Cold-blooded Dinos



>
>Sea turtles manage to keep an almost constant body temperture, not through
>endothermy, but "gigantothermy". I don't know of this is a real term (its
>used The Complete T. rex).
>
>I think that most of the large dinosaurs could have stayed relatively active
>simply by being big. Since heat-loss is a function of surface area, a
>doubling in size would quadruple the surface area - considerably less than
>the increase in mass. So large animals cool down much slower than small ones.
>

An interesting slant on the debate. Earlier this year I attended a
conference near Tumbarrumba (southern N.S.W.) and Gordon Grigg presented
preliminary results from experiments involving rectal thermometers and
really big crocodiles (brave stuff). The result is that the larger the
croc, the closer it is to achieving homeostasis (that is constant body
temperature). Basically, the sheer mass of the animal cools more slowly the
larger tha animal is. This  in its self isn't too surprising, that is what
every one expected. What was intriguing was that, extrapolating his data, a
croc would reach homeosatsis at a mass of around 5000kg. While there are
many problems translating this data to dinosaurs, I think that we can
safely say that, through gigantothermy, the really big ones had to be
homeostatic or even had problems getting rid of excess heat, without being
endothermic.

A quick thought experiment: how do you dump heat? You assume an elongate
body form that increases your surface area to volume ratio. Isn't that
exactly what a large sauropod is doing?

Cheers, Paul

pwillis@ozemail.com.au

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