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RE: From Science New, and synonymous sauropods



 

Tim Donovan 

> > Note the loss of some diversity about 2 million years before the
> > end, which suggests another factor causing a preliminary extinction.
>
>Some have suggested that there was a little mass extinction in the
>mid-Maastrichtian, totally unconnected to the K-T. I don't have enough
>literature on it.
>
> Diversity of large dinos definitely declined with the loss of 
> centrosaurines etc.

Apologies if this response seems rushed...

Extinction is a normal part of evolution.  Throughout the Mesozoic there was
a steady turnover of dino species - no contest there.  Certainly, there
appears to have been such a turnover of species *within* the Maastrichtian
of North America and Europe.  In North America, centrosaurines disappear;
but chasmosaurines are still alive and well.  If Cathy Forster is correct,
there were no less than four chasmosaurine species existing at the very end
of the Cretaceous: _Triceratops horridus_, _T. prorsus_, _Diceratops
hatcheri_ and _Torosaurus latus_.  Thus, I would be hesitant about referring
to such faunal turnovers as resulting in a "decrease in diversity".  What is
diversity?

The Maastrichtian gets extra attention - after all, it was the final stage
of the Mesozoic.  But even if you can demonstrate there was a decline in
diversity (!) during the Maastrichtian, you then have to demonstrate that
the K/T extinction represents a culmination of this decline.  Maybe there
were peaks and troughs in dino diversity (!) during other stages of the
Mesozoic.  Again, when it comes to the Maastrichtian, you have to delineate
correlation from causation; I think you're confusing the two.


> One difference between the Morrison and Nemegt is the presence of 
> therizinosaurs-presumably high feeders-in the latter, which probably was
> at the expense of sauropod diversity.

Only if you can demonstrate (a morphometric study of teeth would be useful)
that sauropods and therizinosaurs targeted the same types of vegetation.



Tim