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Re: Dinosaurs versus mammals
I've got to add my own two cents worth here. I think the most significant
difference between the therapsids and the archosaurs, and the main reason
the archosaurs were the "firstest with the mostest", was reproductive rate.
The archosaurs were able to fill more niches more quickly after cyclic mass
extinctions for this reason alone. The fossil record seems to suggest that
such extinctions are a fact of life; the difference with the few we
normally talk about is the slow recovery of the biosphere afterwards.
Anyway, when the biosphere recovered from mass extinctions during the
Triassic, the group with the highest reproductive rate filled the available
niches first, so becoming dominant. Note that this assumes that the
competitors were at least equal on other terms, which they appear to have
been. Certainly, to have "taken over" from the therapsids, the archosaurs
couldn't have been competitively inferior, which is I feel one of the most
compelling reasons to believe they were endothermic. Note also that the
initial archosaurian victors were mostly the rauisuchians, and not the
dinosaurs themselves. How the dinosaurs came to be victorious over the
rauisuchains is to me the greater mystery. Perhaps they were exhausted from
doing battle with the therapsids?