Re: Tyrant Notes

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

At 12:02 PM 4/5/98 PDT, Miguel de Sosa wrote:

>       I've been looking at various cladograms available on the web (Mike
Keesey's and Stan Friesen's, mostly) and they both seem to say that all
Lancian tyrannosaurs of North America should be included in Tyrannosaurus.
This includes Nanotyrannus lancensis and Dinotyrannus megagracilis.

Well, most agree that the "Jordan theropod" (Olshevsky's Stygivenator
molnari) is a distinct taxon, and not a subadult Tyrannosaurus.

>Also, they say Maleevosaurus novojilovi should be in included in T. bataar
or T. efremovi (what's the diff between these two, anyway?).

Not much.  T. bataar is the first named specimen, is larger than all of the
"T. efremovi" fossils, and shares a few features with T. rex not found in
the smaller Mongolian skulls.  However, most paleontologists consider T.
bataar and T.efremovi to be the same species, and the former name (which
would be the adult) has priority.

>I would like to know the popular opinion on this theory.  Is this widely
accepted, or a  "heresy" (a la Bakker)?

The name "Dinotyrannus" has so far only been used by George Olshevsky.  Greg
Paul coined "Albertosaurus megagracilis" for a specimen he now considers a
subadult T. rex.  (I agree with Greg on this point).  Ralph Molnar
considered this a distinct species in his original report and in his later
review of the Tyrannosaurus skull anatomy: I don't know what his current
thinking is.

In my 1997 Society of Vertebrate Paleontology presentation on tyrannosaurid
systematics, I found that Nanotyrannus and Maleevosaurus formed the sister
taxa to "true" Tyrannosaurus based on character distribution.  This could be
explained in two ways: a) they are adults of the sister taxa to
Tyrannosaurus; b) they are subadults, and the features which united the
larger forms were simply the adult characteristics of Tyrannosaurus.

>        Are they simply growth stages, or can they be put in subgenuses of
Tyrannosaurus?  And if the former, I'd like to know where that was
published, if it has been.  (Sorry, just curious, didn't mean to sound
rude.)  I thought I read somewheres that the Nanotyrannus skull was from an
adult.  Or maybe I just like the idea of "pygmy" tyrannosaurs running
around.  But that's just a fetish...um, never mind.

Thom Carr and Rick Essner have written a paper suggesting the juvenile
nature of the Nanotyrannus skull.  It has not yet been published, but has
been presented at a couple of scientific conferences.

>       I'm probably sounding like an idiot right now, but sorry, I don't have
access to much more than Science, and I can make a trip to the U of Houston
library if I need to find Nature, but those other obscure journals are
pretty tough for a high school junior to get a hold of.  And I probably am
making gross anatomical errors in my judgement, but I had to teach myself
dinosaur anatomy using "The Dinosauria", so I may actually be clueless.

Pick up a copy of Farlow & Brett-Surman's _The Complete Dinosaur_ (Indiana
Univ. Press), which has a fairly good chapter on dinosaur anatomy (with a
major typo or two... :-( ).

>       Oh yes, one more thing on the subject of tyrannosaurs.  In Horner's "The
Complete T. rex", he mentions 4 undescribed species: a "stretch-snouted"
daspletosaur, a Horseshoe Canyon (?)daspletosaur, a non-Albertosaurus
libratus , and a Tyrannosaurus/Daspletosaurus intermediate.  Anybody know
what's up with these guys?  It's been 5 years since the book came out. 

The "strech-snout" daspletosaur is the specimen on display at Chicago's
Field Museum of Natural History (under the inappropriate name
"Albertosaurus").  It will be redescribed by Currie & Bakker.

The Horseshoe Canyon daspletosaur is awaiting description, probably by Currie.

The "non-Albertosaurus libratus" is Gorgosaurus libratus, the proper name
for this animal.  The reasons for placing Gorgosaurus libratus in
Albertosaurus are no longer accepted, so the old name has been restored.

The "Tyrannosaurus/Daspletosaurus intermediate" is the Daspletosaurus seen
in (among others) Horner's _Dinosaur Lives_ and the forthcoming Brett-Surman
& Holtz book _James Gurney's World of Dinosaurs_.  It will be described by
me, Phil Currie & Dave Varricchio in our copious free time...

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