Sources of variation in extinction rates, turnover, and diversity of marine invertebrate families during the Paleozoic

The authors present a new method that can be used to estimate taxonomic turnover in conjunction with stratigraphic range data for families in five phyla of Paleozoic marine invertebrates. Encounter probabilities varied among taxa and showed evidence of a decrease over time for the geologic series examined. The number of families varied substantially among the five phyla and showed some evidence of an increase over the series examined. There was no evidence of variation in extinction probabilities among the phyla. Although there was evidence of temporal variation in extinction probabilities within phyla, there was no evidence of a linear decrease in extinction probabilities over time, as has been reported by others. The authors did find evidence of high extinction probabilities for the two intervals that had been identified by others as periods of mass extinction. They found no evidence of variation in turnover among the five phyla. There was evidence of temporal variation in turnover, with greater turnover occurring in the older series.