ANTAGONISTIC EXTINCTION AND ORIGINATION AMONG THE SEVEN FORMS OF RARITY

Rarity or commonness is among the most important taxonomic traits. However, there are many different forms of rarity and their relative influences on macroevolution are poorly known. Rarity affects extinction risk and if ancestral and descendant taxa are similarly rare then a trend in declining rarity over time should result. Using the Paleobiology Database, we investigate associations between extinction risk and forms of rarity for skeletonized marine animal genera through the Phanerozoic. To quantify rarity, we focus on the effects of local abundance, habitat breadth, and geographic distribution, normalizing these variables to account for temporal variation in the quality of the preserved and sampled fossil record. Using multiple logistic regression, we find a consistent positive association between geographic range and survivorship that varied in strength through time. After accounting for the effect of geographic range, neither local abundance nor habitat breadth consistently predicted patterns of survivorship. Although extinction is consistently biased against narrowly-ranging genera, this effect does not produce a secular trend toward broader geographic range size, in part because origination is consistently biased towards genera possessing small geographic range and narrow habitat breadth. The antagonistic effects of extinction and origination imply that either the probability of cladogenesis is inversely associated with geographic range or that geographic range is only weakly heritable over these temporal and taxonomic scales.