re: "rare" bones in the Hell Creek

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Look.  The Signor-Lipps effect is present in deep-sea sequences where the
sediment IS the fossils.   We've looked at coccolith and planktic foram
sequences where we have hundreds of thousands of specimens, and S-L is
still there!  You can't get around it.  If you have a few thousand or a few
million fossils scattered over the west, it does show some patterns, but it
doesn't negate the effect.  If you could define any meter of sediment and
follow it all over (which is what the iridium allows us to do), you
probably wouldn't find much.  Furthermore, suppose you find a fossil
someplace in the bottom .5 m you refer to (as the Signor-Lipps effect
allows), then we'd argue about the uppermost .5 m.  Then maybe we'd cut it
down to the last .25 m, and we could argue about that.   This is exactly
what the effect predicts--that fewer taxa will be found as you approach the
boundary.  Species diversity towards a boundary always looks gradual--and
you will never know by sampling alone what the truth really is.  It would
be more effective and creative to try to think of other evidence or tests
that can be brought to bear on the issue rather than trying to fight this
effect.


>>...Only a few thousand (dinosaur bones) have ever been found in the Hell
>Creek..."
>
>
>I can't speak with ghreat authority about the "rarity" that represents,
>but the entire eastern Late Cretaceous outcrop has yielded roughly an
>order of magnitude fewer dinosaur bones.  Yet, we seem to see distributional
>patterns (chronological and geographic) in occurrence based on these: for
>example, nodosaurs are unknown east of western Alabama; _Dryptosaurus_
>sensu stricti is unknown pre-Maastrichtian, etc.
>
>The point is that a paltry few thousand specimens over a wide area are
>sufficient to define a pattern.  _If_ thjat pattern shows disappearance
> a meter below the Iridium boundary, it lends credence to the reality
>of the dissappeearance (I wish I could erase prior text on this
>primitive system) as a biological phenomenon rather than as a Signor-Lipps
>effect result.
>
>david schwimmer
>schwimm@uscn.cc.uga.edu

Jere H. Lipps
Professor, Department of Integrative Biology
Director, Museum of Paleontology
University of California at Berkeley
Berkeley, CA 94720
510-642-9006 fax 642-1822
jlipps@ucmp1.berkeley.edu