Confidence limits on fossil ranges that account for facies changes

A drawback to most existing methods of calculating confidence limits on fossil ranges is their assumption that the probability of collecting a taxon through a stratigraphic section is constant. Marshall (1997) described an approach that would circumvent this problem, but it requires knowing the probability of collection as a function of stratigraphic position. Multivariate paleoecological methods, such as detrended correspondence analysis (DCA), offer a means of estimating these probabilities. DCA axis 1 sample scores can be used to quantify facies change through a stratigraphic section, and to calculate the probability of collection of a taxon relative to DCA axis 1. From these two, the probability of collection of each taxon can be estimated for each horizon in the measured section. This approach is applied here to the Upper Ordovician Kope formation of the Cincinnati, Ohio, area to distinguish between disappearances of taxa that are driven by facies change and taxon rarity and those that represent true regional extinction. This new approach to confidence limits could also be applied to test the synchroneity of extinction or origination at large-scale turn-over events, such as mass extinctions and the turnover pulses that bound episodes of faunal stasis.