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Re: Tyrannosaur Evolution




On Saturday, February 12, 2005, at 08:49 AM, Mickey Mortimer wrote:

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?
Many possible theories, including the newly introduced tyrannosaurids chasing down and killing their competition, or scaring them to the point of petrification from their own meals. If it wasn't for Homo sapiens industrialization redndering so much of North America undiggable, we'd have a much better idea.

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 believe there's an 8-inch claw as well, presumed to belong on the hand. Imagine if it turned out to be a foot claw. .

I don't know how big any of the fragmentary specimens is, do you?
"The Encyclopedia of Dinosaurs" estimate is 18 feet for the known specimen. Also, it is mentioned that the specimen was found in marine deposits in New Jersey, suggesting that the poor guy drifted out to sea before becoming fossilized.

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.
I imagine the Western Interior Seaway[and the nasty critters in it] had a good deal to do seperating the Eastern & Western faunas.