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Re: Breakup of Pangaea



>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.  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.

Not all wet, but not quite correct on time scale.  Pangaea began breaking up
just about the beginning of the age of dinosaurs (Late Triassic and Early
Jurassic).  Up through the Late Jurassic, there was considerable similarity
between dinosaurs of all the regions of the world.  However, by the
Cretaceous, drifthing continents and rising inland seas caused the various
lineages of the dinosaurs to diverge.  Dinosaurs of the southern continents
(Gondwana), for example, were very different from those of Asiamerica, with
Europe as a sort of "buffer zone".  However, it must be remembered that the
Cretaceous is longer (by 15 million years) than the whole of the Cenozoic,
so this division would be very difficult to link to the K/T extinctions.

On the other hand, the last 8 million years of the Cretaceous ( the
Maastrichtian stage) are notable for a drastic drop in sea level, removing
the inland seas and allowing flow of animals between long seperated
regions.  Bakker suggests the spread of disease as a possible extinction
agent, while others suspect climatic changes caused by this drastic change
in geography and circulation.

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Phone:301-405-4084