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RE: Same genus? Tyrannosaurus and Tarbosaurus

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Is there now any strong reason to place Tarbosaurus, found in
> Mongolia and China, in a different genus than Tyrannosaurus -
> other than geographic?
>  It seems to me, from what information I have, that the
> morphological difference between the two is so slight that it is
> within the realm of possibilty that they might be two "races"
> belong to the same "species."  Of course, we'll never know the
> absolute true answer until DNA samples of both are collected,
> thoroughly analyzed for genome sequences, and compared - an event
> which will probably never be possible.

We wouldn't even know then, since there are no REAL guidelines about how
much genetic diversity can be present in a "species" before we split them
into different "species.

> But there may be stronger reasons for putting each in a different
> genus that I have not yet learned.

There are substantial anatomical differences in the skulls of Tarbosaurus
and Tyrannosaurus, most recently illuminated by Sabath and Hurum:
Hurum, J.H. & K. Sabath. 2003. Giant theropod dinosaurs from Asia and North
America: Skulls of Tarbosaurusbataar and Tyrannosaurus rex compared. Acta
Palaeontologica Polonica 48: 161?190.

That being said, known (and even better unpublished) specimens do show some
substantial shared derived features present in Tarbosaurus and Tyrannosaurus
that are not (yet) found in Daspletosaurus.

So, in my opinion, it is best to keep them as separate genera (contra my
earlier work).

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