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Re: Theropod "migrations"



In a message dated 4/24/99 12:38:57 PM EST, larryf@capital.net writes:

<< So......I guess there could have been a Cretaceous Bering land bridge after
 all. >>

As far as I can determine, a robust Cretaceous Bering land bridge did exist 
until sometime early in the Santonian, when it vanished as the sea level rose 
to flood Laurasian continents with the Turgai and Kansas epicontinental seas. 
At this point eastern and central Asia became isolated from other continents 
and their faunas began to diverge: you will find many of the same families in 
Asia and North America (whether dinosaurs, mammals, birds, or whatever), but 
they evolved different genera in the Campanian and Maastrichtian when the two 
regions were physically separate. When the sea level started to fall in the 
late Maastrichtian, the Bering land bridge may have reappeared, so if we ever 
do find late Maastrichtian faunas in Asia they may turn out to contain North 
American genera and even species. The latest known Mongolian dinosaur-bearing 
facies, the Nemegt Formation, is almost certainly several millions of years 
older than the Lance/Hell Creek of North America, and was laid down when the 
Bering land connection was still severed.