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RE: New in Science



> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> ELurio@aol.com
> Sent: Friday, May 11, 2001 8:57 AM
> To: qilongia@yahoo.com; dinosaur@usc.edu
> Subject: Re: New in Science
>
>
>
> In a message dated 5/11/01 12:56:00 AM, qilongia@yahoo.com writes:
>
> << the Triassic-Jurassic Boundary Mass Extinction >>
>
> There was no Triassic-Jurassic Boundary mass extinction, the
> event took place
> between the Norian and Rhietian stages of the late Triassic.

On land, yes.  In the seas, however, there is a big extinction event at (or
very close to) the Tr-J boundary: conodonts wiped out, ammonoids and some
other groups suffer major crashes, etc.

> Why
> the Jurassic
> begins with the Lias instead of the Rhietian an interesting
> question that I
> don't know the answer to.

Because Period boundaries were established using marine invertebrates rather
than the rare terrestrial vertebrates.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796