Differences in extinction selectivity and their relationship to functional traits in late Cenozoic mollusks.

Identifying generalizable patterns of extinction selectivity is crucial for understanding the mechanisms driving extinction processes. Differences in the trait composition of extinct surviving species may represent evidence of processes of extinction selectivity during the past. Here, we leverage the information from the late Cenozoic molluscan fossil record and extant biota from the western Atlantic coast of North America, to test for differences in the trait composition of extinct and surviving species of bivalves and gastropods. We found basal metabolic rate (BMR) is the trait most closely associated with the extinction patterns observed in our data. On average across all studied molluscan species, odds of survival decrease by ∼11% for every 1-milliwatt (mW) increase in BMR, but this pattern was consistent only for bivalves. BMR thus represents an organismal trait that scales up to predict species survival in bivalves. By contrast, a variety of other functional traits shown to be important in other taxonomic and temporal contexts, including shell composition in bivalves and shell structures such as varices and the callus in gastropods, were not found to be associated with survival. This could suggest some of these traits, sometimes posited to represent important organismic adaptations, may not have played a prominent role in long term species survival in Cenozoic bivalves and gastropods. A variety of biotic and abiotic factors may likely determine the extent to which particular organismal traits influence patterns of species survival.