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RE: Nanotyrannus

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Buckaroobwana@aol.com
> Dr Holtz,
> I recently heard that the specimen once called Nanotyrannus lacensis is
> actually a juvenile T.rex. Is this the case? When it was first
> examined, it
> was determined to have adult characteristics such as fused skull
> bones, if I
> remember right. What was discovered about this creature to result in its
> reidentification? If anybody else on the list has information, it
> would be
> appreciated.

This subject has been much discussed on the list before: check out the
Dinosaur List Archives (http://www.cmnh.org/fun/dinosaur-archive/index.html)
for previous postings.

In short form, however:
Thomas Carr recently re-examined the skull in some detail.  He could not
confirm the presence of the skull fusion that was previously cited.
Instead, he noticed the surface of the skull is covered with woven bone
texture typical of juvenile archosaurs.  Furthermore, the main differences
between this skull and those of a definite _T. rex_ are the same as the
differences between juvenile and adult _Gorgosaurus_ specimens.  Finally,
the type of "Nanotyrannus" does have a number of derived features otherwise
found only _T. rex_.

This was published in his paper:
Carr, T.D. 1999.  Craniofacial ontogeny in Tyrannosauridae (Dinosauria,
Coelurosauria). Journal of Vertebrate Paleontology 19: 497-520.

I can confirm these observations personally; and have additional character
evidence supporting a placement for this skull close to other _T. rex_
specimens in terms of shared derived features.  The simplest explanation at
present: _Nanotyrannus_ is a juvenile _T. rex_.

However, I can think of two major discoveries which would falsify this
I) Discovery of a large adult tyrannosaur which is not _T. rex_ but instead
showed derived features otherwise present only in _Nanotyrannus_;
II) Discovery of a juvenile tyrannosaur OF THE SAME SKULL LENGTH (or
smaller) as _Nanotyrannus_ which showed a greater number of derived features
of _T. rex_.  ("Tinker" does not count: it is considerably larger than the
_Nanotyrannus_ type).

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): 301-314-7843