CHANGES IN DRILLING AND PEELING PREDATION ON TURRITELLID GASTROPODS ASSOCIATED WITH THE PLIOCENE WESTERN ATLANTIC REGIONAL MASS EXTINCTION

The Plio-Pleistocene regional mass extinction of molluscan fauna of Florida and the US Atlantic coastal plain was followed by a period of rapid origination, resulting in similar modern regional species richness. Predator and prey relationships were impacted by high extinction rates across all taxa. Previous studies have suggested that the extinction is associated with a possible system-wide decline in predation intensity, but data from additional prey species both prior to and after the extinctions are needed to determine how general this pattern may be. We examined predatory trace fossils on turritellid gastropods, a clade which experienced substantial extinction during this time. Overall rates of peeling predation on turritellid gastropods across the extinction boundary decreased – with turritellid species having an average peel-repair frequency of 0.41 in the Plio-Pleistocene compared to a frequency of 0.16 in modern samples. However, in the two surviving lineages, Turritella perexilis and Torcula exoleta, peel-repair frequency was similar in the Plio-Pleistocene samples and in modern samples. Fossil T. perexilis had a peel frequency of 0.26, compared to the modern samples’ peeling frequency of 0.14. Fossil T. perattenuata had a peeling frequency of 0.18, while its descendant, T. exoleta, had a peeling frequency of 0.17. Additionally, the incidence of multiple attacks in modern samples is markedly lower. While a majority (89%) of turritellid species went extinct during this event, most fossil species had higher peel-repair frequencies than fossils of the surviving lineages. In contrast with peeling frequency, the frequency of drilling predation on modern descendants is higher than their fossil ancestors (0.21 vs 0.02 and 0.14 vs. 0.11 for T. exoleta/T. perattenuata and T. perexilis, respectively). Across all species, drilling increased from an average of 0.11 in the Plio-Pleistocene samples to 0.19 in modern samples. These results suggest that as turritellid prey diversity decreased, predators may have adapted to attack surviving species, or these lineages may have become more vulnerable to their predators.