CRETACEOUS TO MODERN TRENDS IN DRILLING PREDATION AND PARASITISM ON ECHINOIDS

Predatory cassid and parasitic eulimid gastropods are known to produce drill hole traces in modern echinoid tests, however these traces are relatively understudied in the fossil record. Here, we present preliminary results of Cretaceous to modern trends in drill hole frequency, compiled from the newly established Echinoid-Associated Traces (EAT) Database. The aim of this database is to elucidate macroevolutionary trends in trace-producing behaviors targeting echinoids, by assembling data on frequency, morphology, size, location, selectivity, and ecology of drill hole and other trace occurrences on echinoid tests, through study of museum specimens and primary literature surveys. Preliminary analyses focus on observing changes in drill hole frequencies during important evolutionary events in the history of tracemakers and their echinoid targets, such as the diversification of cassids and eulimids in the early Cenozoic, the radiation of infaunal echinoids in the Cretaceous, and the K-Pg and Eocene-Oligocene extinctions. Currently the majority of the available EAT Database trace occurrence data represents echinoids from the southeastern U.S. (Florida, Georgia, Alabama, Mississippi, Texas, North Carolina), reflecting initial focus of this project on Florida Museum specimens and field collecting in the region. Preliminary observations show, as expected, near absence of drill hole occurrences in the Early Cretaceous. This is followed by a gradual increase in drill hole frequencies through the Late Cretaceous and Paleogene (up to 30%), coinciding with the appearance and diversification of the proposed tracemakers. Average drill hole frequencies drop significantly across the Eocene-Oligocene boundary, concurrent with an extinction of echinoid taxa (approximately 20% species loss). Predatory and parasitic drill hole average frequencies track each other, though predatory drill holes are generally more common. Modern drill hole frequencies, compiled from the primary literature, vary greatly between populations, but generally occur at much higher frequencies than those observed in the fossil record. Preliminary trends imply escalating intensity of these biotic interactions over the evolutionary history of the gastropod tracemakers.