Resumen de Dissecting a Marine Snail Species Radiation (Conoidea: Turridae: Polystira) Over 12 Million Years in the Southwestern Caribbean

Jonathan A Todd, Kenneth G Johnson

• The specialized carnivorous conoidean Polystira comprises the largest marine snail species radiation in the neotropics with approximately 120 living species known and a rich neogene fossil record. Here we analyze its patterns of species richness, origination, and extinction over the past 12 My in the southwestern caribbean (SWC). Taxic analysis of a database comprising 3344 specimens and 114 species shows species richness and sampling intensity to co-vary over this interval. Richness is lowest in the late miocene (pre-NN11), then rises and remains approximately constant until the recent, when it rises sharply. No large peaks in fossil origination rates occur, though extinction rates may increase between 2 and 1 ma. Well-sampled extinct species had median durations of 0.8-1.75 My, but the large majority of species are rare, confined to one or a few horizons, and have durations of <1 My. Polystira shows the highest species origination rates recorded among marine gastropods (0.585-0.935 My-1), combined with short species durations; 94% of living species evolved within the past 1.6 My. This contrasts with longer durations and slower speciation rates in the hyperdiverse conoidean Conus, but that pattern requires restudy. High post-isthmian diversity-coinciding with increased habitat heterogeneity-contrasts with the massive decline in SWC species richness in another carnivorous gastropod-the "strombinid" columbellidae. We suggest that diversification of Polystira has been driven by intrinsic feeding-related specialization, whereas regionally the near-extinction of scavenging, non-specialized "strombinids" is a direct response to an extrinsic decline in seasonality and variation in food supply that supports trophic generalism.