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As I understand it, the clay layer at the K-T boundary only caught
Walter Alvarez's eye because of its placement. I am forced to wonder, if
a impossibly huge analysis of sedimentary rocks across geologicic history
was conducted, exactly how many anomalous irridium spikes would turn up.
Quite a few I'd imagine. Is the deposition of the K-T layer a direct
result of the impact? If so, is there anything particularly disctinctive
about it (other then the irridium spike) that might help to identify other
potential "impact clays"?
How controversial is Paul Sereno's placement of _Euparkeria_ at the
base of Archosauria, its dissasociation from the ornithosuchids, and the
placement of the ornithosuchids with (Gauthier's) pseudosuchians to form
Cruotarsi? These last two seem pretty radical based on the little
research I've done, and I was curious what other people's take on it was.
Sereno 1991 is the most up to date thing on it I've read on "thecodonts"
(even _I_ don't mind using quotation marks for THAT paraphyletic group).