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Re: Extinction Question and a Thank You!

On Sat, 5 Feb 2005 22:06:54 -0600, Dora Smith <villandra@austin.rr.com> wrote:
> Maybe it depends on what you call a crocodylian?

That's why I specified "Cenozoic clades".I this is unclear, what I
meant is the least exclusive clades containing the Cenozoic members.
In the case of crocodylians, I believe this would be the same as the
crown clade, that is, the closest common ancestor of gavialids,
crocodylids, and alligatorids, plus all descendants. And this ancestor
arose in the Cretaceous, as far as we can tell.
> They actually evolved before the dinosaurs from their common ancestor.

The total (or panstem) clade evolved before dinosaurs from their
common ancestor, but this included many taxa (ornithisuchids,
aetosaurs, phytosaurs, poposaurids, rauisuchids, sphenosuchids,
mesosuchids, etc.) which would not be considered crocodylian. The
closest common ancestor of all crocodylians which survived the end of
the Mesozoic appeared during the Cretaceous, as did the closest common
ancestor of all Cenozoic sharks, if I am not mistaken.
-- Mike Keesey