TRENDS IN PREDATION AND PARASITISM RECORDED BY DRILL HOLES IN PALEOGENE ECHINOIDS

Echinoid-associated drill-holes recording predatory and parasitic behaviors are relatively understudied and underutilized in paleontological research. In modern settings, cassid and eulimid gastropods are implicated as the tracemakers. Cretaceous-to-Paleogene trends in frequency, diversity, size, and selectivity of drill-holes are, therefore, of particular interest because they span the time of radiation of these two gastropod groups and their echinoid prey/host. The oldest presumed predatory and parasitic drill-hole traces are known from the Late Cretaceous, shortly after the first appearance of fossil cassids and eulimids. Both of these groups experience a diversification in the Paleogene. Frequency of drill-hole traces on fossil echinoids are expected to track the diversity of these tracemakers, but prey/host characteristics, such as diversity, abundance, distribution, and infaunalization, likely play an important role as well. Here, we present preliminary analyses of trends in predatory and parasitic behaviors using Paleogene Atlantic Coastal Plain echinoid data from the Echinoid-Associated Traces Database (EAT-D), currently under construction, and which once complete, will encompass Triassic to Recent trace occurrences. Preliminary observations show relatively high trace frequencies in the Eocene (up to 30%), with a subsequent decrease in both predatory and parasitic trace frequency (to 8%) across the Eocene-Oligocene boundary, coincident with a 22% reduction of echinoid species diversity. Interestingly, cassid species do not experience a significant diversity decrease across this boundary, while eulimid species experience only a moderate decrease (14% of species), suggesting that both predator/parasite and prey/host diversity may be important factors in determining the frequency of these biotic interactions.