Tyrannosaurs, dwarf, early, and otherwise...

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

Howdy, folks.

A couple of major summaries of the information in question are forthcoming
in the next few months/year.  Some quick reviews:

"_Nanotyrannus_" is a juvenile.  Most of the alledged fusions of the skull
previously reported cannot be confirmed by subsequent examination.  The bone
texture is very clearly juvenile, however.  The specimen demonstrates clear
_Tyrannosaurus_ and _T. rex_ synapomorphies.  In almost every case, those
features in which it differs from adult _T. rex_ are those features which
differ from juvenile and adult _Gorgosaurus_.  The simplest explanation is
that it is a juvenile _T. rex_, although the possibility does remain it is a
juvenile of an as yet otherwise unknown Hell Creek _Tyrannosaurus_ species.

"_Alb./Dinotyrannus megagracilis_"'s identity is less certain.  Those
features that do differ from adult _T. rex_ are also found in subadult (but
not necessarily adult) _Gorgosaurus_.  It is very likely a subadult _T.
rex_, but more complete material may demonstrate it is unique.

Earliest tyrannosaurids: _Alectrosaurus olseni_ is the oldest named definite
tyrannosaurid.  Older material includes teeth from Aptian-Albian of Asia and
the Cenomanian of North America.  If _Siamotyrannus_ is a tyrannosaurid, it
is even older (Barremian).  _Stokesosaurus_ (a Late Jurassic form) has been
referred to Tyrannosauridae or Tyrannosauroidea, and is even older still;
its placement here, however, remains uncertain.

All these forms are smaller than classic Campano-Maastrichtian tyrannosaurids.

Hope this helps.  Keep watching the skies... er, journals (and books).

                        Thomas R. Holtz, Jr.
                        Vertebrate Paleontologist
Deptartment of Geology                  Director, Earth, Life & Time Program
University of Maryland                  College Park Scholars
College Park, MD  20742       
Webpage: http://www.geol.umd.edu        Phone:301-405-4084
Email:tholtz@geol.umd.edu               Fax:  301-314-9661