ESTIMATING THE DURATION OF A MASS EXTINCTION ACCOUNTING FOR SIGNOR-LIPPS EFFECT

A key question in studies of mass extinctions is whether the extinction was a sudden or gradual event. This question may be addressed by examining the locations of fossil occurrences in a stratigraphic section. However, due to the Signor-Lipps effect, the fossil record can be consistent with both sudden and gradual extinctions. Rather than being limited to rejecting or not rejecting a particular scenario, ideally we should estimate the range of extinction scenarios that is consistent with the fossil record. In other words, rather than testing the simplified distinction of “sudden versus gradual,” we should be asking, “How gradual?”

Wang et al (2012) described a method for answering the question “How gradual could the extinction have been?” by developing a confidence interval for the duration of a mass extinction. For example, the method can be used to estimate with 90% confidence that an extinction took place over a duration of 0.3 to 1.1 million years, or 24 to 57 meters of stratigraphic thickness. However, their method assumed uniform preservation and recovery, which is unrealistic. Here we describe a new method for estimating the duration of an extinction event that does not assume uniform recovery. We also implement a binary search algorithm to speed up the computation time by an order of magnitude. The method incorporates the Adaptive Beta Method of Wang et al (2016) to allow for increasing or decreasing fossil recovery potential. We illustrate its use with data from Late Cretaceous ammonites from Seymour Island, Antarctica.