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RE: Warm Blooded vs. Cold Blooded



>I think that the whole idea of dinosaurs as cold blooded animals is out =

>dated and can't stand up under any kind of scrutiny.

I don't think dinosaurs were cold blooded, but I've yet to be convinced =
that they were fully endothermic.

While for small species endothermy holds considerable benefits, for =
larger animals the cost becomes very high.

If you take the example of a lion and an alligator, both are of similar =
mass, but the lion must consume roughly ten times as much to survive. To =
put it another way, a herd of 100 antelope could sustain ten alligators, =
but the same herd could only sustain one lion.

So the question is, can a large sauropod, with only a small mouth, =
swallow enough food to stay alive? Was the earth capable of growing =
enough food to feed large numbers (which there appear to have been) of =
these creatures?

Shifting the emphasis slightly, I do think most dinosaurs were (at least =
nearly) homeothermic.=20

For those not familiar with the terminology, endothermic means the =
animal generates heat by burning food (as mammals and birds do), =
homeothermic means it maintains a constant body temperature. All modern =
homeotherms are also endothermic.

However large crocodiles and leatherback turtles maintain a much more =
regular body temperature than small lizards, simply by virtue of their =
size. Much larger dinosaurs would have kept an almost constant =
temperature. I'd say their temperature would fall by a couple of degrees =
during the night, and would take most of the next to rise by the same =
amount. Variation in their temperature would be seasonal rather than =
daily.

Predator-to-prey ratios do indicate a endothermic predators, but I think =
there are too many other factors to make any assumptions from this (for =
example differences in lifestyle could make plant-eaters more likely to =
be fossilized). Even if we can, that says absolutely nothing about the =
metabolism of the prey.

If by "out-dated" you mean "unfashionable," then I must agree. However, =
this does not make it wrong. There are lots of good arguments for =
endothermy, but there are also good arguments for ectothermy. We must =
not allow fashion to dictate scientific thinking.

Sorry if I've gone on a bit, but I don't think we have enough evidence =
to settle this either way.

All the best,

James Shields