Re: All kinds of odd extinct observat...

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Me, too.  But lots of this ground has been covered before, even on
PaleoNet.  Seven months ago we discussed the Signor-Lipps effect, which
accounts for a good deal of the biostratigraphic record being discussed
here.  The biases and sampling error inherent in S/L-E account for most of
the problem worldwide.  What this means, as we tried to explain in our
original paper, is that the fossil record per se cannot descriminate
between sudden extinctions and gradual extinctions; therefore paleontology
has little to say about the time period of the extinction event or the
mechanism.  I, too, would argue that all the taxa going extinct "near" the
end of the Cretaceous (or any other extinction boundary) tell us something
very important.   But it's unlikely to be the mechanism itself.

Paleontology, for example, could not descriminate between an impact that
produced an extinction and a 1000 year change in paleoceanography that
eliminated surface plankton, shallow-water benthos, and reefs, as well as
changed continental climates and eliminated terrestrial biotas.  (Not too
silly either, as El Ninos today accomplish much of that in a single
year--mass mortalities in all those groups, and at least one extinction; so
hold one of those for a decade, and you probably can have another mass
extinction.)

What we need to do, it seems to me, is to define carefully (using the
entire biota, stable isotopes, and paleobiogeography) the pre- and
post-extinction environments.  That's not been done well enough yet
(especially the post-) to set limits on the actual mechanism.  After all,
the asteroid did not clobber each and every individual--it somehow changed
the environment and that caused the extinction, if you believe in killer
asteroids.


Jere H. Lipps,  Director
Museum of Paleontology
University of California
Berkeley, California 94720 USA

Voice:  510-642-9006.  Fax:  510-642-1822
Internet:  jlipps@ucmp1.berkeley.edu