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Late Maa North American tyrants (was RE: Validity of Alioramus)

> From: Demetrios M Vital <vita0015@umn.edu>
> Is Nanotyrannus lancensis late Maastrichtian like Tyrannosaurus
> rex?


> I was
> under the impression that all tyrannosaur fossils from the
> Maastrichtian of
> North America are assigned to T. rex.  Is this true?

Kind of.  _Albertosaurus sarcophagus_ is a distinct form from the early
Maastrichtian of North America, but some people have referred any
tyrannosaurid fossil from the late Maastricthian of North America to _T.

Actually, there are two styles for these referrals:
I) Uncritical: "Hey, I found a tyrannosaurid from the late Maastrichtian of
western North America!"  "Then it must be _T. rex_."

II) Critical: "Hey, we've examined the late Maastrichtian tyrannosaurid
fossils from western North America, and found them to be consistent with
being different growth stages and variations of a single species,
_Tyrannosaurus rex_".

Other tyrannosaurid taxon names for late Maastrichtian western North
American dinosaurs include _Stygivenator molnari_ (originally _Aublyosodon
molnari_), _Dinotyrannus megagracilis_ (originally _Albertosaurus
megagracilis_), and _Nanotyrannus lancensis_ (originally _Gorgosaurus
lancensis_).  However, many workers now consider most or all of these
species to be different growth stages of a single species, _Tyrannosaurus
rex_.  This does not preclude, however, the discovery and/or demonstration
of a second tyrannosaurid species from the late Maastrichtian of western
North America.

Hope this helps.

                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