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Re: Multicausal mass extinctions?

> what is the Signor-Lipps effect?

Probably better explained somewhere in the archives; the statistical
phenomenon that if you draw a line anywhere in the fossil record, search a
short part of the formation under it and compare this with a much longer
part under the same line you will see a drop in abundances and you'll be
able to claim that there was a gradual extinction. This is due to the simple
fact that not all fossils are equally frequent. A very beautiful example
exists in the book "Night Comes to the Cretaceous" by James Lawrence Powell
(1998): There someone dug a meter or less into a recent seashore. The deeper
they dug the more taxa they found; hadn't they known that all were still
alive they would have had to suppose that a gradual extinction is going on
right now, or has just stopped, among seashells.