Re: Nature of the fossil record

[Stefan Bengtson <Stefan.Bengtson@xxxxxxxxx>]

Norm & Doug: Aren't we confusing the issue when trying to identify
physical causes for the Signor-Lipps (or Sig-Lipps, or Phil & Jere, or Tom
& Jerry, or whatever) Effect? It is a statistical phenomenon: whenever
recovery is less than 100% complete, an instant mass extinction will look
blurred in our records, in that some taxa will seem to disappear before
the actual event. Stated thus, it allows a null hypothesis to be defined,
assuming that probability of recovery does not vary (or varies in a
knowable way) throughout the sequence. How often does that happen...?

The problem is that we have to deal with the real world (always
this annoying reality!), in which chances of recovery are governed by
a number of non-random factors, only some of which can be controlled.
Collecting bias and lithology can be, at least to some extent, but other
factors cannot. If we knew the true ranges, we could calculate the 
recovery probabilities; and if we knew the recovery probabilities, we 
could calculate the true ranges. It's a kind of uncertainty principle. So 
I guess the only thing the S&L Effect tells us is that the fossil record 
is blurred. True, Pete Sadler's and Charles Marshall's work on confidence 
intervals for the ranges of fossils in continuous sequences is slightly 
more uplifting, but for specific problems such as the barren meter that 
started this discussion, only presences will tell us anything real, not 
absences. 

Biostratigraphy is not impossible, just imprecise. As Jere implies, we
need the physical events to acquire true precision. (And the physical
evidence needs biostratigraphy to tell one impact or sea-level change from
the other.)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Stefan Bengtson
Institute of Earth Sciences
(Historical Geology & Palaeontology)
Norbyvagen 22
S-752 36 Uppsala
Sweden

tel. +46-18 18 27 62 (work)
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