Dissecting a Marine Snail Species Radiation (Conoidea: Turridae: <I>Polystira</I>) Over 12 Million Years in the Southwestern Caribbean

Abstract

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.