continental fits & land bridges

["Bonnie Blackwell, x 3332" <bonn@qcvaxa.acc.qc.edu>]

One aspect of Larry's reply is a bit inaccurate.  The continents first
collided to form Pangea well before the evolution of the dinosaurs.
>From the mid-Triassic on, they are beginning to pull apart again.
What happens in the late Cretaceous, is that the sea level changes
drastically several times.  When the sea level is high, the dinosaur
populations are isolated, not by deep seas, but primarily by shallow
(not more than 50 - 100 m likely) seas (called epeiric seas).
When these drain off the continent, then areas that were previously 
separated, like the area around the rockies and the eastern n.am. area,
are suddenly reunited as one land mass.  

As for the "land bridges", these could be considered to be areas where
the continents have not yet completely pulled apart.  in times with high
sealevels, these might be flooded or very narrow, thereby preventing or
severely restricting species movement.  they may have also been very
inhospitable places - like death valley, which would have limited species
movement just as effectively as inundation.  in times of low sealevels,
these connections would have been broader, perhaps more hospitable places
to cross between continents. 

b

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bonnie Blackwell,                               bonn@qcvaxa.acc.qc.edu
Dept of Geology,                                (718) 997-3332
Queens College, City University of New York,    fax:  997-3349
Flushing, NY 11367-1597

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bonnie Blackwell,                               bonn@qcvaxa.acc.qc.edu
Dept of Geology,                                (718) 997-3332
Queens College, City University of New York,    fax:  997-3349
Flushing, NY 11367-1597