PATTERNS OF MOLLUSCAN PREDATION IN THE OLIGOCENE BYRAM FORMATION OF VICKSBURG, MISSISSIPPI
Out of 83 bivalve and gastropod genera in the samples, 43 showed signs of drilling (34 in C, 30 in E, and 32 in G). Fourteen genera were drilled in all horizons, 16 were drilled in two horizons, and 17 were drilled in a single horizon. Absence of drilling more often reflected the lack of a rarer species in a horizon. All shells have not yet been recounted as whole vs. fragmented specimens, which is necessary to calculate drilling frequencies (DF). However, all 21,274 shells have been examined for drillholes (~1150 overall) and preliminary results indicate that the number of drillholes in whole shells compared to the number of total shells in each horizon indicate similar levels of drilling predation. If shell fragmentation is similar across horizons, DF should indicate ecological persistence. Taxa that are both common and more frequently drilled across horizons include Corbula, Crassinella, Euspira, Natica, Scapharca, and Turritella. Ongoing work will include separation of whole vs fragmented specimens in order to calculate DF and prey effectiveness as well as to do additional research in exploring relationships to abundance, size, and other data on drilling in this formation.