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The Plio-Pleistocene turnover event in the western Atlantic following the closure of the Central American Seaway involved high rates of extinction for both gastropod and bivalve molluscs. This extinction was associated with declining nutrient conditions and has been presumed to be associated with a decrease in molluscan body size. Previous work which has been concordant with this expectation, however, has either focused on bivalves or not considered the effects of the recovery post extinction. In three phylogenetically diverse clades, we found that body-size evolution in gastropods across the turnover event is likely tied to ecology. One clade increased in size, one decreased, and another exhibited no substantial change. Individual species lineages exhibit a mixture of microevolutionary changes from the Pliocene to today. This study indicates that gastropod body-size evolution may be more complex than in bivalves, with ecology and other functional traits playing a significant role. Macroevolutionary processes, especially whether a clade re-radiated post extinction, were found to be important. Indeed, a low portion of extant diversity consists of survivors from clades that increased in size or have similar size distributions among their species relative to the Pliocene. 

The influence of functional traits on species survivorship has been evaluated in various contexts in both modern and ancient ecosystems, but an important direction for research is to integrate datasets that include both extinct and extant taxa. This approach can provide a more reliable understanding of the effects of functional traits on macroecological and macroevolutionary dynamics. Knowledge of the links between individual traits and survivorship is crucial for developing accurate extinction risk predictive models. Here we test the impact of numerous functional traits on the survival and extinction of species through time, using bivalve and gastropod species from the rich fossil record of the western Atlantic over the last ~3 million years, along with the associated extant biota. We also compare the impact of these organismic traits on survival relative to a group level trait: geographic distribution. Analyses use a dataset of 12 functional traits including life habit, feeding behavior and basal metabolic rate (BMR), for 115 species from 36 families. Traits were observed and measured from specimens in the collections of the Paleontological Research Institution, Florida Museum of Natural History, and University of Kansas, as well as surveys of the literature and online databases such as the Neogene Marine Biota of Tropical America (NMITA). Results derived from Principal Coordinates Analysis (PCoA) show there is a clear distinction between extinct and extant species, overall, when comparing them based on life habit, maximum body size, shell composition and BMR. Most traits showed little direct relation with survival, except BMR and associated maximum body size, supporting the Metabolic Theory of Ecology. Since many functional traits do not explain survival, their function may be mis- or over-interpreted, and traits posited to represent important organismic adaptations may not play a prominent role in long-term species survival, especially during the major climate changes over the last ~ 3 million years. Some traits do show significant interactions, and these were more fully explored using additional multivariate analyses. The relative importance of geographic range size suggests group-level characters may be the primary determinant of extinction patterns over macroevolutionary time scales. 

Turritellid gastropods are among the most widespread, abundant, and diverse mollusks in Plio-Pleistocene deposits of the Atlantic coastal plain and Florida, with at least 46 species and subspecies described over almost two centuries. Yet the systematic status of these common fossil species and their phylogenetic relationships—to each other and to turritellids living today in the western Atlantic—have never been investigated in detail. We make use of recent molecular phylogenetic work on living turritellids and new analyses of shell characters to review the group from this time interval to the present in a comprehensive phylogenetic analysis and assessment of their evolutionary history in the region. We conclude that 20 fossil and two Recent species are valid. Four of these species are placed in the genus Torcula Gray, 1847; five in Caviturritella new genus, and eleven in “Turritella” sensu lato. We identify Torcula perattenuata as the likely direct ancestor of one of the two turritellid species living today off the southeastern U.S. coast, Torcula exoleta, and we elucidate the fossil record of the other extant species, “Turritella” perexilis (senior synonym of Turritella acropora). We show that Caviturritella was extirpated from the United States Gulf and Atlantic coastal plains in the Early Pleistocene but is still represented in the western Atlantic by the living species C. variegata in the southern Caribbean. We also present the first detailed treatment of Plio-Pleistocene turritellid fossils from Georgia. Our analysis shows that the Plio-Pleistocene Pinecrest beds of Florida contain 18 co-occurring turritellid species, which is the highest turritellid species diversity in one formation known in the fossil record.