A COMPARISON OF SCLEROCHRONOLOGICALLY DETERMINED GROWTH AND LIFESPAN DATA AMONG 3 CLADES OF CO-OCCURRING TURRITELLID GASTROPODS IN PHYLOGENETIC CONTEXT

Turritellid gastropods are both extremely common and diverse in assemblages from the Plio-Pleistocene to Recent of Florida and the US Atlantic coastal plain. These have long been of paleontological interest, but understanding has been hampered by lack of detailed modern phylogenetic analysis. Three clades of turritellid gastropods distinguished by molecular phylogenetics are identifiable using morphological synapomorphies; Vermicularia, Torcula, and a new genus characterized by hollow-newel morphology (“Caviturritella”). Molecular data indicates that Vermicularia and Torcula are sister taxa, but the hollow-newel clade is only very distantly related to these species. We have therefore constructed phylogenies for Pliocene–Recent members of each of these clades independently based on morphological characters. Species assignable to “Torcula” included T. apicalis†, T. cookei†, T. clarksvillensis†, T. clarionensis, T. radula, T. perattenuata†, and T. exoleta. Species assignable to “Caviturritella” included C. alumensis†, C. banksii, C. gonostoma, C. pontoni†, C. magnasulcus†, and C. terstriata†, with the extant members of the clade confined to the eastern Pacific, but included in the phylogenetic analysis.

Oxygen isotopic sclerochronology was used to determine growth rate and life history data for the majority of the species in each clade. Observed maximum lifespans were less than 3 years for non-Vermicularia species, but notable disparity was observed in both maximum size and size at 1 year in age. We were therefore able to place these life-history characteristics in phylogenic context and examine how life history characteristics evolved in each co-occurring clade, under changing environmental conditions, including whether the productivity changes and western Atlantic turritellid extinctions associated with the closure of the Central American Seaway impacted each clade similarly. This extinction appeared to be selective both on protoconch size and maximum body size for the non-Vermicularia turritellids. By examining life history data we can disentangle whether this change in maximum body size was accomplished by changes in maximum lifespan, initial growth rate, or growth rates after the first year of life and whether distantly related clades of turritellids responded in similar ways.