ABUNDANCE AND SURVIVAL ACROSS THE END-CRETACEOUS MASS EXTINCTION: PATTERNS IN COASTAL PLAIN BIVALVES

Ecological studies of living taxa suggest that rare species are more prone to extinction than abundant ones, but the possible influence of abundance on survival during mass extinctions has received little attention. In this study, I examine the relationship between abundance and survivorship across the end-Cretaceous (K/T) mass extinction in Late Maastrichtian bivalve subgenera from the North American Coastal Plain. The data used in these analyses were compiled from data collected by Norman Sohl and Carl F. Koch and include 256 localities spanning ten formations and 293 bivalve species representing 121 subgenera. These data were supplemented with information on taxonomy, body size, ecology, and shell mineralogy. I found little evidence linking survivorship with abundance or geographic extent in these data. Results were robust to abundance metric, spatial scale, taxonomic scale, data treatment, and statistical test used and did not appear to be influenced by body size or feeding mode. When selectivity was assessed within shell mineralogical and ecological groups, calcite-bearing and epifaunal survivors were significantly more abundant than victims. This introduced the possibility that the relationship between survivorship and abundance is obscured in taxa with poorer preservation potentials, but when level of shell organic content was used as a proxy for preservation potential, I found no evidence that selectivity differed according to preservation potential. The fact that abundance does not promote survivorship in K/T bivalves suggests that the factors influencing survivorship during mass extinctions in the fossil record may differ from those operating at ecological timescales.