More SVP: Nanotyrannus & teeth

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

As I get caught up on other things, another SVP tidbit:

In the discussion over whether Nanotyrannus is its own taxon or a baby T.
rex, someone from the audience (one of the Bobs Sloan?) brought up a point
which argued against the case he was trying to make.  (I was going to point
this out in my discussion time, but I never leave time for discussion...).

He noted that in the Hell Creek, no one every finds small Tyrannosaurus rex
teeth, only "Nanotyrannus" teeth.  These teeth never overlap in size.  This
he used as evidence that they were different taxa.

One might argue instead that the lack of overlap is in fact evidence that
they are the SAME taxon, and that "T. rex" style teeth only occur later in
growth.  This would explain why nobody finds small "T. rex"-style teeth:
because as juveniles, they have "Nanotyrannus" style teeth.

Oh, and for those wondering: the Field Museum tyrannosaur is not
Albertosaurus, and the "Gorgosaurus"-like features on it are plaster.  It
may be a new species of Daspletosaurus (as Currie & Bakker think), but some
of the key regions to identify Daspleteosaurus are also restored on it...
In any case, as many people noticed, the feet of the mounted skeleton are a
little weird, in that it has two digits IV on one foot, and two digits II on
the other...  Oh, well.

Got to get ready for the next advisee.  Later, all.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661