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RE: Tyrannosaur Evolution



> From: Tim Donovan [mailto:uwrk2@yahoo.com]
> Sent: Sunday, February 13, 2005 7:31 AM
>
> --- "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>
> wrote:
> >
> > B) That being said, what limited we know of the
> > eastern North American dinosaurian fauna suggests
> > rather smaller animals in general.
> > Some possible contributing factors include:
> >     1. Smaller geographic ranges (some hypotheses
> > suggest that the largest animal size correlates with
> > the available geographic range.
> > I don't entirely buy that, but I'd thought I'd throw
> > that out)
>
>   It's not even true. Western North America was then a
> relatively narrow north south strip of land. The east
> was considerably larger, yet Dryptosaurus was much
> smaller than T. rex.

Well, only if you limit the continent involved to "western North America" 
rather than "Asiamerica".  Still, as I said, I don't buy
it...

> >
> > >  So I don't
> > > think we have a good idea of the variation that
> > existed there and then.
> > > Western North America had its own smaller basal
> > tyrannosauroid too
> > > (Labocania), and the Nemegt had Bagaraatan.
> >
>
>   But Labocania was only of Campanian age. So
> Bagarataan was a tyrannosauriod, not a troodont?

Bagarataan's position is far from certain, but it does come out as a basal 
tyrannosauroid in my latest analyses (see Dinosauria II).

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
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