RE: 100 MA North America

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

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of john-schneiderman@cox.net
> Sent: Monday, October 10, 2011 5:19 PM
> To: dinosaur@usc.edu
> Subject: 100 MA North America
> 
> Does the basal tyrannosaurs Appalachiasaurus and Dryptosaurus 
> from Appalachia [eastern North America] trace its roots 
> directly back to the Late Jurassic Stokesosaurus, middle 
> Cretaceous Cedar Mountain tyrannosauroid, the european 
> Eotyrannus, or Asian tyrannosaurs?

Not enough is published yet on the Cedar Mountain form to tell. However, most 
recent phylogenetic analyses place Appa. and Drypto.
as closer to Tyrannosauridae proper than to the Asian Xiongguanlong (and 
Raptorrex, if that is indeed a distinct taxon), and much
closer to these than to Stokesosaurus, Eotyrannus, Dilong, or the 
proceratosaurids.

Nevertheless, things become somewhat muddled on this point. The position of 
Asian Alectrosaurus is not certain: it is in the same
grade, certainly. It appears that Bistahieversor is closer to Tyrannosauridae 
than are the Appalachian forms.

So at present it looks like the ancestor of the entire clade "Appalachian forms 
[grade] (?+Alectrosaurus) + (Bistahieversor +
Tyrannosauridae)" may be Asian, but that most of the radiation within it was 
within North America, with subbranches (Tarbosaurus,
Alioramus, Zhuchengtyrannus) returning to Asia during this interval.

(Note, however, "returning to Asia" is a bit of a muddled concept anyway: 
during at least some of this time Laramidia and
eastern/central Asia are one connected landmass).

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, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

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