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Geological periods



I had thought that there was consensus about the dates used for
Triassic/Jurassic/Cretaceous, but apparently the reference I've been using
for my latest project is contradicted by some later material.

Sattler's DINOSAURS OF NORTH AMERICA (1981) gives:
        Triassic 190-225 mya
        Jurassic 140-190 mya
        Early Cretaceous 100-140 mya
        Late Cretaceous 65-100 mya

But, in trying to track down why one reference thinks Dilophosaurus might
have been Late Triassic and another calls it Early Jurassic, I ran into
this schedule; it's in Lessem's KINGS OF CREATION, and matches the one in
the Dino Society Encyclopedia -

        Triassic 208-245 mya
        Jurassic 145-208 mya
        Cretaceous 65-145 mya

So we agree on the end of the Cretaceous, but we're 5 million years
different on its beginning; we differ by 18 million years on the beginning
of the Jurassic; we differ by 20 million years on the beginning of the
Triassic.

Is there that much dispute, or has there been a systematic reorganization
of the periods, or what?


Steve Jackson, sj@io.com - this will do till I fix my .sig file . . .