TAXON AGE AND SELECTIVITY OF EXTINCTION

Taxon-age distributions were compiled for families of marine animals surviving or becoming extinct in each stage of the Phanerozoic. I demonstrate, through the use of a modified bootstrap analysis, that there is no difference between the longevity of families becoming extinct during times of background extinction and times of mass extinction. In both mass and background extinction intervals the mean age of families that become extinct is 2 standard deviations below the geometric mean taxon age of families available for extinction. Young families are more susceptible to extinction, perhaps as the result of lower species richness or of occupying a smaller geographic range. There is no tendency during mass extinctions toward loss of families with different taxon ages other than those that become extinct during background times. Thus, in terms of family survival, mass extinction appears to be an exaggeration of processes of background extinction.