Re: Nature of the fossil record

[Peter Sheehan <sheehan@xxxxxxxxxxxxxxxx>]

Biostratigraphy works because, as Bob Kleinpell loved to point out, 
"boundaries must be drawn with a wide brush, not not a finely pointed pen."
And this is because of what we now call the Signor-Lipps Effect.


On Mon, 9 Jan 1995, N. MacLeod wrote:

> I really don't want to belabor this point (and I certainly don't want Doug
> to feel like he's being picked on) but Doug's comment shows just how
> insidious the S&L Effect is and how easy it is to see whatever we want to
> see in it's image.  Is the Signor-Lipps Effect PRIMARILY a preservation
> phenomenon?  Any particular Signor-Lipps pattern might be due to
> differential preservation.  But then again it might be due to sample
> size/relative abundance interactions, or ecological changes.  That's the
> problem with negative evidence.  You simply can't know precisely why
> something is not there.  Signor and Lipps (1982) list three sources for the
> effect without indicating which one is dominant.  Within it's domain the
> S&L Effect is simply a statement of uncertainty.  But there must be a
> domain outside of which the S&L Effect can be ignored.  If this isn't true
> then I guess I don't understand how biostratigraphy is possible.
> 
> Norm MacLeod
> 
> 
> 
> >to reinterate what Jere has said in a slightly different way - the point
> >of the Lipps(-Signor) Effect is that is establishes the correct null
> >hypothesis against which to measure the observed patterns in the fossil
> >record.  Contrary to Peter Harries comments, the L(-S) Effect is PRIMARILY
> >a preservational phenomenon.  The effect is exacerbated by collecting
> >bias and can be reduced by increased collecting effort.  However it cannot
> >be completely negated by increased collecting.  Correctly identifying the
> >null hypothesis is critical in all of this, and is all to infrequent in
> >paleontology.
> >Doug Erwin
> 
> 
> 
> ----------------------------------------------------------------------------
> Norman MacLeod
> Senior Research Fellow
> N.MacLeod@nhm.ac.uk (Internet)
> N.MacLeod@uk.ac.nhm (Janet)
> 
> Address: Dept. of Palaeontology, The Natural History Museum,
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> 
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