RE: Tyrannosauridae

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Paleo_Mont
>
> judith river formation:
> _Albertasaurus sarcophagus_'Flesheating lizard from Alberta'
> (nice name)
>
> two medicine formation:
> Gorgosaurus liberatus  not sure on the name there.

_Gorgosaurus libratus_ means: free (as in "freely moving") Gorgon lizard.

Not quite.

The type, and so far all specific diagnostic material, of _Albertosaurus
sarcophagus_ is from the Horseshoe Canyon Formation.  The type, and so far
all specific diagnostic material, of _Gorgosaurus libratus_ is from the
(stratigraphically lower) Dinosaur Park Formation.  However, there is
additional material (a good skeleton from the Two Medicine, for instance)
which have yet to be studied in detail which might belong to one, the other,
or neither species.

There is a LOT of tyrannosaurid material throughout the Judithian and
Edmontonian of the Western Interior which might be from either of these two,
or _Daspletosaurus_, but at present telling these two apart from postcrania
is similar to telling _Centrosaurus_ from _Styracosaurus_ without their
heads...

Both are relatively gracile forms, compared to "bruisers" like _Daspleto._,
_Tarbo._, and _Tyrannosaurus_.

                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