Re: Breakup of Pangaea

[John Alroy <jack@homebrew.uchicago.edu>]

I'm not a paleogeographer, but on the other hand, this issue is  
probably of limited interest to the group so a couple of comments  
should suffice. The breakup of Pangea started in the Triassic. The  
Triassic Newark Supergroup in eastern North America is an ancient  
rift valley associated with the split from what is now northwestern  
Africa, similar to the great rift valley in East Africa. The opening  
of the Caribbean happened after this in the Jurassic, and by the  
Early Cretaceous North America was completely isolated from the other  
continents and the South Atlantic was fully opened. None of these  
tectonic events are clearly associated with continental extinctions,  
but I imagine you could make a case for marine extinctions somewhere  
in the Mesozoic resulting from the connection of previously isolated  
seas - nothing in particular comes to mind, but I don't work on  
marine fossils. Continental separations seem not to have had much  
effect on terrestrial biotas, but the sudden erection of land bridges  
due to sea level changes is closely associated with a few major  
extinctions, e.g., the Eocene-Oligocene mammal extinction in Europe  
and the late Pliocene mammal extinction in South America.
As for the latitude of North America, I believe this was pretty much  
the same in the Late Cretaceous as it is now. Whereas previously  
(particularly in the late Paleozoic) latitudinal shifts made a big  
difference for North American organisms, by this time it couldn't  
have been a major factor.