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Quo vadis J-K extinctions? (was RE: Big Craters)
> From: firstname.lastname@example.org [mailto:email@example.com]On Behalf Of
> << >But there certainly is quite a change in the nature of the
> dinosaurs worldwide fas one crosses the J-K boundary.<
> There is? What is it? I still see diplodocoid and
> sauropods, stegosaurs, ankylosaurs, small compsognathid and big
> and spinosauroid theropods milling about. No sudden changes at anything
> except the generic level. >>
> This is just what I was referring to. Large diplodocoids and
> pretty much vanish across the J-K boundary, replaced by much smaller
> sauropods; abundant stegosaurs are gone from North America (only
> rare Chinese
> and European forms survive into Early Cretaceous) and are replaced by
> ankylosaurs. Don't recall any spinosaurs from the Jurassic; they
> all seem to
> have arisen in the Early Cretaceous, maybe to fill a niche vacated by
> extinction of allosaurids. Theropod systematics is still too
> unsettled to be
> certain which groups successfully crossed the J-K boundary. The
> extinction is
> not as well defined as the K-T extinction, but I think there's something
> there worth looking into.
Sure, there's something worth looking into IF AND WHEN PEOPLE FIND A
TERRESTRIAL J-K SEQUENCE (with vertebrate fossils)!
The Morrison dinosaurs are Kimmeridigian, or maybe earliest Tithonian. The
Lakota Formation, Yellow Cat Member of Cedar Mountain Fm, and good Wealden
Group dinosaur assemblages are Barremian.
We are missing good assemblages from the Tithonian (latest Jurassic),
Berriasian, Valaginian, and Hauterivian dinosaur assemblages: over 20
million years of dinosaurs!
This is like using dinosaurs from the late Coniacian (85 Ma) and mammal
assemblages from the earliest Paleocene (65 Ma) to argue for the asteroid
impact hypothesis of the K-T boundary. You can fit the whole series of
changes from the Aquilian to the Judithian to the Edmontonian to the Lancian
within this time frame.
Thomas R. Holtz, Jr.
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
College Park, MD 20742
Phone: 301-405-4084 Email: firstname.lastname@example.org
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-314-7843