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Re: Warm bloodedness in archosaurs before dinosaurs
At 09:03 PM 6/17/97 -0700, Joshua Dyal wrote:
>... From Bakker's book, I had almost gotten
>the impression that the thecodonts must have mostly been endothermic,
>but to my surprise, I don't see how that can be. The reason is that
>the crocodilians are very high up on the cladogram, cutting off at
>least half of the thecodonts. I suppose it is possible, especially
>if warm-bloodedness were "new" to the archosaurs, that crocodilians
>could have dropped their metabolism back to ectothermic levels.
It doesn't even have to be all that "new" to be lost, in my opinion. Being
endothermic is not always such a great thing. It is expensive. So I could
well see an aquatic ambush predator, like modern crocs, losing endothermy:
after all, water is a fair temperature buffer on its own, and an ectotherm
need not catch as much prey.
In short, it is not at all out of the question for endothermy, or
proto-endothermy, to be plesiomorphic for the post-proterosuchid clade (I
forget its name), and lost in eucrocodilians (the modern sort), or perhaps
in mesocrocdylians (where they apparently returned to the water).
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