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Re: Breakup of Pangaea



From: "Larry Lynch, Univ of Wis-Eau Claire" <LYNCHLD@cnsvax.uwec.edu>
 > 
 > Regarding dinosaur extinctions, I haven't seen much reference to the
 > effects of continental drift and the breakup of Pangaea as a possible
 > influence on dinosaur survival.  By the end of the Cretaceous, Pangaea
 > was coming apart, as I understand it, and it appears from maps I've
 > seen that North America was headed from the north temperate zone
 > from a previous position in the tropics. 

More or less.  But the main issue is one of timing and climatic
gradients.  The break-up was well under way, even by the middle
part of the Cretaceous, long before the big extinctions (in
fact there were one or two lesser mass extinctions in the Late
Cretaceous prior to the big one).

Also, until the very end of the Cretaceous, the climatic gradients
were very shallow, and "tropical" climates extended to about the
modern Canadian border, and "warm" climates existed throughout zone
covered by the major Canadian fossil beds.

Even at the very end, the whole Earth was far warmwr than it is now,
and the main change was apparently increased seasonality due to
the lowering sea levels.

 >  Is this an accurate
 > impression, or am I all wet?  (I am strictly an interested amateur
 > in all this.)  It seems to me that there would have been a drastic
 > climatic change as a result of all this.

There wasn't as much as you would think, but what is more,
much of it happened about the same time as the typical Late
Cretaceous dinosaur groups first began to become important,
that is the time when hadrosaurs and ceratopsians started to
become a major part of the ecology.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.