Endothermy

Endothermy, which probably evolved separately in the groups, almost requires that the pulmonary and somatic loops be separate, which works with a septum in the ventricle. It's most likely convergence, not ancestral.

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... Personally, I suspect that most theropods were endotherms, like their surviving cousins. One problem with the question is that it assumes that endothermy has to apply for an entire group, because the examples found today work that way (if you ignore examples in fish).

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Well, endothermy does.

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... animals are also known as (ahem) homeotherms. they generate their own heat internally to maintain a constant body temperature... endothermy means an organism that does such a thing. >>Cold-blooded animals or poikilotherms have a changing body temperature in relation to their ...

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