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RE: Validity of Alioramus



As for _Alioramus_: there actually ARE a few potential synapomorphies of
this taxon with _Tarbosaurus_ and/or _Tyrannosaurus_.  However, it currently
falls further down my tree than these guys plus _Daspletosaurus_ plus
_Gorgo._ + _Alb._.  Wouldn't be too surprised, however, it it might not
creep further up with more information.

That being said, I think that the extremely well-developed nasal crests,
among other features, preclude _Alioramus_ from being a juvenile of
_Tarbosaurus bataar_.

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> rbi
>
> Speaking of problematic tyrannosaurids, what is the current view of
> Nanotyrannus?  I have examined the actual specimen, and it sure
> doesn't look
> like just a juvenile T. rex to me!  However, I am far from being
> able to give
> a qualified opinion...thus I ask how others feel about it being a
> valid taxon?

Thom Carr's 1999 paper in JVP has pretty well established the juvenile
status of this individual.  Additional, as he mentions, there are some
derived features in this skull otherwise only found in _T. rex_.  So, we
could validly argue a couple of positions:
        *_Nanotyrannus_ is a valid taxon, closely related to _T. rex_, known at
present only from a juvenile skull
        *"Nanotyrannus" is a specimen of juvenile _T. rex_.

At the Armour Symposium, Currie argued for the former, and Brochu & I for
the latter, although none of us with particular fervor.  There are a couple
of hypothetical specimens which would help establish the validity of
_Nanotyrannus_ as its own taxon:
        *An adult specimen of tyrannosaurid which was distinct from _T. rex_ and
which clearly showed derived features shared with the _Nanotyrannus_ type
        *A juvenile specimen of tyrannosaurid of the same length as the _Nano._
skull which was distinct from _Nanotyrannus_ and which also showed clear _T.
rex_ synapomorphies not found in the _Nano._ skull.

Note that the "Tinker" specimen is MUCH too large to help clear up the
latter situation: the teeth of "Tinker", for example, have roots so long
that if you tried to place them in the _Nano._ maxilla they would blast out
through the top of the skull!

Barring the discovery of either of the hypothetical specimens discussed
above, I'm willing to take the route of accepting "Nanotyrannus" as a
juvenile _T. rex_.

                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