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FW: Theropod "migrations"



<I think it could have happened that way, yes. Especially if the continents
<were separated with no land bridge between. And yes, I think tyrannosaurs
<did get big "in a hurry", that`s why we don`t find many of intermediate
<size.

        Then again, there would be no reason to think that Tarbosaurus and 
Tyrannosaurus were really closely related at all, and therefore not necessarily 
any reason to assume they diverged AFTER the breakup of Pangea.  It seems more 
reasonable to follow the dogmatic mainstream line of reasoning that the 
immediate common ancester of Tarbosaurus and Tyrannosaurus was a large, 
flightless Late Cretaceous tyrannosaur, probably generically indistinguishable 
from the two, that had to find a way to get from one continent to the other 
without flying.  
     As far as land bridges are concerned, during the Cretaceous there were 
multiple transgressive and regressive sequences of varying magnitude.  It would 
be surprising if land bridges WEREN'T constantly popping up and dissappearing.  
Considering that various regions of the crust were also being uplifted and 
eroded down throughout the period (there were three orogenic events in the 
Cordilleran region during the Cretaceous of North America alone), it also 
wouldn't seem surprising if these bridges didn't always pop up in exactly the 
same places.

LN Jeff