A geographic test of species selection using planktonic foraminifera during the Cretaceous/Paleogene mass extinction

Species selection has received a great deal of theoretical attention but it has rarely been empirically tested. It is important to determine the level of selection that operated during a particular extinction event because it can help distinguish between traits that were actually responsible for extinction and those that were merely correlated with it. Here, we present a test that can help distinguish between organismal and species-level selection, which we demonstrate using the high-resolution fossil record of planktonic foraminifera species recorded in deep-sea sediment cores. Our test examines the fate of survivors and victims during the Cretaceous/Paleogene (K/Pg) mass extinction within single geographic regions, where all individuals experience the same selection pressures. Selection at the organismal level implies that individual members of surviving species are more fit than those of victimized species, and therefore should be more likely to survive in affected areas; conversely...