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Thanks for letting us know.
Going back to one of your original points about endotherms having really high energy expenditures... It's true that they use a lot of energy to maintain their body temp (I think I've heard somewhere in the order of half of all energy consumed is used to generate body heat, but don't quote me on that), but that obviously gives them a huge advantage over ectotherms. So while it is costly, the price is obviously well worth it.
It might be interesting to note that various degrees of endothermy have evolved on about four separate occasions:
Birds
Mammals
Brooding pythons
Leatherback turtle
That gives you an idea of how advantageous it can be.
One theory on the evolution of endothermy in mammals is that it allowed them to be active at night, and therefore avoid the mouths of hungry, diurnal reptiles. It's possible that their high and stable body temps allowed the mammals to flourish after the catastrophic event that spelled doom for most of the dinosaurs.
Stewart
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