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RE: had a thought - dimorphic tyrannosaurs? was RE New fossils provide clues to tyrannosaur/ornithomimid evolution




> -----Original Message-----
> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of Anthony Docimo
> Sent: Wednesday, April 22, 2009 2:22 AM
> To: dinosaur@usc.edu
> Subject: had a thought - dimorphic tyrannosaurs? was RE New 
> fossils provide clues to tyrannosaur/ornithomimid evolution
> 
> 
> 
> Had a thought when I read this:
> 
> > Subject: New fossils provide clues to tyrannosaur/ornithomimid 
> > evolution 
> > 
> http://www.chicagotribune.com/news/local/chi-dinosaurs-found-field-mus
> > eumapr22,0,5569868.story

These critters are pretty impressive: more when the papers are out.

> 1.  Tyrannosaurids are Ornithomimids?

Ummm, no. Although the first tyrannosaurid limb material found in the US was
thought to be from a giant species of Ornithomimus.

> 2.  Wait a ...*remembers the giant arms of the (Gobi?) with 
> no body*...could that have been a tyrannosaur?

Nope. Almost certainly not. Deinocheirus is almost certainly an
ornithomimosaur (until demonstrated otherwise)>

> 3.  Like with sharks and early whales - the males have the 
> claspers to grip, while the females don't need them...similar 
> thing with turtles and curved bellies.
> 4.  If any male tyrannosaurs are known with small forearms, 
> perhaps either they are genetic abnormalities, a species-wide 
> exception, or the skeleton was assembled with someone else's 
> arms.  (there's precedent - sauropod heads)

There are relatively good skeletons of many tyrannosaurids from North
America and Asia, and none show a hint of giant arms. If you buy the
robusticity dimorphism arguments of Larson, then we definitely have arms of
both male and female arms in tyrannosaurids, and they are all small.

> I realize the odds are exceedingly small, but I thought that 
> either it would help in some way (in however much of a 
> round-about way), or a small thing to offer a chuckle over; I 
> don't mind.

The chuckle part could work. Interesting idea!

However, there is now a very good history for both the ornithomimosaurs
(going back to the Early Cretaceous) and the tyrannosauroids (back to the
Middle Jurassic), and they are separate and distinct throughout that time.
Beishanlong and Xiongguanlong add to this information; as you will see when
the papers come out, there is overlap between the skeletons and they are
quite distinct.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-405-0796

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA