LEVERAGING PALEOCLIMATE DATA TO EVALUATE THE EVOLUTIONARY HISTORY OF GROWTH AND LIFESPAN IN THE TURRITELLIDAE (CAENOGASTROPODA): CHALLENGES AND OPPORTUNITIES

Serial sclerochronologic analysis of mollusk shells can be used to simultaneously explore ecology and life history in paleoenvironmental context, making it an invaluable tool for evolutionary paleoecology. Sclerochronologic interest in the Turritellidae, primarily for paleoenvironmental reconstruction, has produced over 135 ontogenetically calibrated isotope curves representing more than 50 species. Turritellids are ideally suited for these analyses as they are abundant, marine, and have aragonitic skeletons that readily show diagenetic alteration. By examining what factors may influence growth rate, lifespan, and adult size we can elucidate the evolutionary history of this abundant fossil taxon and the relative impact of abiotic conditions in their life histories.

Although large, this data set is currently biased towards younger records; turritellids first appear in the Late Jurassic and are diverse throughout the Cenozoic, but approximately 80% of isotopically-studied species are from the Neogene and Recent. There is also a notable bias towards North and Central American localities. These limitations notwithstanding, abiotic environmental factors might have less of an effect on turritellid life history parameters than those observed in bivalves, with phylogenetic history and biotic interactions inferred to have more influence on the evolution of these traits in turritellids.

Preliminary results suggest that high latitude settings do not appear to promote longer lifespan in turritellids, but rather correspond to slightly smaller maximum body sizes and reduced rates of growth. Species with maximum lifespans between 1 and 3 years, achieving a variety of maximum sizes frequently co-occur in many assemblages. Species with longer lifespans are rare but occur at both high and low latitudes. Long lifespan is associated with the genus Vermicularia, but also observed in several normally-coiled turritellids achieving a variety of maximum sizes and distributed from the tropics to high latitudes. The contrast between bivalves and turritellids emphasizes that data from a diverse set of taxa are essential to understanding the evolution of molluscan life history parameters.