Reduced strength and increased variability of extinction selectivity during mass extinctions

Two of the traits most often observed to correlate with extinction risk in marine animals are geographic range and body size. However, the relative effects of these two traits on extinction risk has not been investigated systematically for either background times or during mass extinctions. To close this knowledge gap, we measure and compare extinction selectivity of geographic range and body size of genera within five classes of benthic marine animals across the Phanerozoic using capture-mark-recapture models. During background intervals, narrow geographic range is strongly associated with greater extinction probability, whereas smaller body size is more weakly associated with greater extinction probability. During mass extinctions, the association between geographic range and extinction probability is reduced in every class and fully eliminated in some, whereas the association between body size and extinction probability varies in strength and direction across classes. While geographic range is universally the stronger predictor of survival during background intervals, variation among classes during mass extinction suggests a fundamental shift in extinction processes during these global catastrophes.