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Re: Extinct vs Disappeared

At 9:56 AM -0800 3/5/10, Andrew Simpson wrote:
>With Stegosaurs it is often said that they went extinct midway through the
>Cretaceous. This always bothers me slightly as I prefer the phrase
>'disappeared from the fossil record' over the word extinct do to the fact
>that disappeared from the fossil record is a factual statement were as
>went extinct is speculative. I for one tend to assume that Stegosaurs
>would have likely still existed in small remote niches and on islands
>where advanced predation and food niche taking new herbivores with better
>defenses couldn't get to them and thus wouldn't cause their end.
>Am I being nit-picky?

Not at all. In fact, this is an active area of research by paleontologists
and statisticians. The issue, as you state, is that there will likely be a
gap between the last fossil find of a taxon and its actual extinction
(unless we are lucky enough to find the last Stegosaurus that ever lived).
How big is this gap, or "range extension"? It can be very large; the
classic example is the coelacanth, which disappears from the fossil record
after the Cretaceous but actually is not extinct at all.

Here are two classic papers on this subject:

Strauss, D., and P. M. Sadler. 1989. Classical confidence intervals and
Bayesian probability estimates for ends of local taxon ranges. Mathematical
Geology 21: 411-427.

Marshall, C. R. 1990. Confidence intervals on stratigraphic ranges.
Paleobiology 16: 1-10.



Steve C. Wang
Blauistein Visiting Associate Professor of Geological Sciences
   Stanford University
Associate Professor of Statistics
   Swarthmore College