[Thread Prev] [Thread Next] [Thread Index] [Date Prev] [Date Next] [Date Index]

Re: Supernova causing P/T boundry mass extinctions?



>On Thu, 5 Jan 1995, Tom Holtz wrote:
>
>>
>> Maybe we have to chalk up the missing meter to the Signor-Lipps effect.
>>
>Given the number of man hours that have gone into trying to find
>vertebrate fossils in that meter section, I have hard time just
>explaining it away through the Signor-Lipps effect.  That tends to come
>into play when things have been sampled in a relatively uniform fashion.
>This interval, however, certainly doesn't suffer from being under
>examined.  Therefore, the lack of fossils, be it caused by some primary
>or some drastic post-depositional processes, would seem to be real.
>
>Peter Harries

You may not believe that Signor-Lipps had anything to do with it, but mere
effort is not enough to overcome that effect.  It will always be there no
matter how much you look.  It has nothing to do with uniformity of sampling
either, as the sampling error and biases are present no matter how you do
it.  Furthermore, negative evidence is no evidence at all, especially in
view of an effect like Signor-Lipps.  You can feel about it anyway you want
(I have my own feelings about what happened), but the Sig-Lipps effect has
nothing to do with feelings and everything to do with data.  What Sig-Lipps
says is that the expected condition will be a gradual decrease (of varying
magnitude depending on a variety of original and ensueing conditions) in
species diversity towards any set boundary, whether it be artificially
placed or natural.  What that means is only that you cannot separate a
gradual extinction from a catastropic one because all extinctions look
gradual because of sampling error and bias of preservation and spatial
distribution of the biota.  It does not mean that a catastrophe did not
take place or that all the bones were dissolved by acid--it means you must
seek other evidence not subject to the Sig-Lipps effect.


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