COMPARING THE AGE SELECTIVITY OF MODERN EXTINCTIONS WITH PHANEROZOIC BACKGROUND AND MASS EXTINCTIONS

Much research on the current biodiversity crisis has focused on the rate of modern extinctions compared to that known from the fossil record. Here we compare modern extinctions and Phanerozoic extinctions with respect to their age selectivity. We evaluate age selectivity using logistic regression to quantify the relationship between extinction risk and genus age. For modern groups, we estimate extinction risk using assessments of threatened species from the International Union for Conservation of Nature (IUCN) Red List. We limit our analysis to genera with both a fossil record as well as substantial evaluation by the IUCN. For fossil groups, we compiled data from the Paleobiology Database supplemented with the Sepkoski Compendium. We confirm earlier findings that for fossil groups, older genera (i.e., those having older origination times) are more likely to survive during background extinctions, but this relationship largely disappears during mass extinction events. For modern groups, we find little relationship between extinction risk and genus age for multiple taxa at the class and phylum levels. Thus, modern extinctions differ from what has been observed in Phanerozoic background intervals, but are instead consistent with dynamics observed in the Big Five mass extinctions.