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Re: Theories on the extinction of dinosaurs



At 12:21 PM 11/14/99 -0500, Dinogeorge@aol.com wrote:
>
>>All< current evidence indicates that non-avian dinosaurs became extinct at 
>the K-T boundary, not at different times in different places.

Part of the problem is that at many localities it is the disappearance of
the dinosaurs that is used to *place* the K-T boundary.  This makes for a
certain circularity in determining if dinosaurs survived the boundary, at
least at these localities.

> There is still 
>some leeway around the boundary because of dating error margins and things 
>like that. This is a relatively short time span, which is why it is difficult 
>to find localities where exactly this time span occurs in the geology. As a 
>counterprediction, let me predict that wherever the K-T boundary occurs at a 
>locality, any dinosaurs at that locality will appear below it and no 
>dinosaurs will appear above it. (This is what is found in the Deccan deposits 
>in India, by the way, which straddle the K-T boundary.

Well, to within the resolution of the Deccans deposits.  Unfortunately
sedimentary layers are widely separated within the sequence, so resolution
is crappy, to say the least.  Because the impact layer seems to occur
within a *volcanic* layer in the Deccans, it is actually impossible to tell
how closely the dinosaur extinction matches the K-T boundary layer.

> According to 
>Chatterjee, dinosaur fossils occur plentifully in the lower parts, then there 
>is the K-T boundary clay, above which there are no more dinosaurs. This is 
>described in his paper on the Shiva crater, another K-T boundary asteroid 
>impact.)

Maybe.  I am not yet convinced that Shiva is an impact crater.

--------------
May the peace of God be with you.         sarima@ix.netcom.com