Re: Fastovsky vs Archibald

[Phil Bigelow <bigelowp@juno.com>]

On Fri, 17 Jun 2005 18:18:20 -0400 Mike Nathal <mnathal4462@wowway.com>
writes:
> In the "Butting Heads" section of the recent Natural History 
> magazine, 
> David Fastovsky and David Archibald debate the K/T extinction.
> 
> I quote Fastovsky:  " ...every published, quantitative, field-based, 
> 
> stratigraphically refined study  addressing this question has 
> concluded 
> that dinosaur diversity was unchanged up to the K/T boundary"
> 
> and Archibald:     "In the last 10 million years of the Cretaceous, 
> but 
> well before the K/T boundary events, the most recent compilations 
> show an 
> unequivocal decline in the diversity of dinosaur species."
> 
> Hard to see how both of these statements can co-exist.    


Au contraire.
Based on current data, both Archibald and Fastovsky are correct.  But
they are essentially talking past each other.

Archibald is correct in noting that taxa counts show a decrease in
dinosaur diversity within the last 10 million years of the Cretaceous
(this is particularly apparent when comparing the dino fauna of the
Judith River/Two Medicine Formations with the dino fauna of the later
Hell Creek Formation).  Ergo, Archibald is looking at extremely long-term
trends.

Fastovsky is correct in concluding that dinosaur diversity WITHIN the
Hell Creek Formation was not in decline up to the K-T boundary.  In other
words, even though their were fewer dino taxa in the Hell Creek Formation
compared to earlier times, there is no evidence that this group was in
steady decline up to the terminal layer.  Therefore, Fastovsky is looking
at a much shorter trend (~2 million years at most), and noting that not
much changed.

That said, some workers have claimed that a Hell Creek nodosaur went
extinct before the K-T boundary.  But considering that ankylosaurids are
generally uncommon in the Hell Creek Formation, there is a good
possibility that the proposed premature nodo extinction may in fact be
only an artefact of sampling/collecting.

<pb>
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