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Re: Tyrannosaur Evolution

Joe Cantrell wrote-

> Why did tyrannosaurs become so large and advanced in western North America
while the east harbored a > frozen relic of the
pre-Baynshirenian-Dryptosaurus- down to the late Maastrichtian?

Keep in mind our record of Eastern North American Late
Campanian-Maastrichtian tyrannosauroids basically consists of one specimen
(Dryptosaurus holotype), six teeth, a partial maxilla and three femora.  I
don't know how big any of the fragmentary specimens is, do you?  So I don't
think we have a good idea of the variation that existed there and then.
Western North America had its own smaller basal tyrannosauroid too
(Labocania), and the Nemegt had Bagaraatan.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html