VARIATION IN BORE HOLE MORPHOLOGY AND DETERMINATION OF GASTROPOD PREDATOR SPECIES

Gastropod borehole data are used to analyze paleoecologic and evolutionary patterns of predator/prey interactions preserved in the fossil record. Variation in frequency and morphology of boreholes found on prey species may be due to differences in either the predator or prey behavior or morphology. For temporally similar assemblages, morphologic differences in predators are likely to be caused by having had different dominant predatory gastropod species. Determining that different predatory gastropod species were responsible for the predatory traces is therefore important. This determination is relatively straightforward for gastropod species that produce bore holes with different gross morphologies. Determining such differences among species that produce similar bore hole morphologies is more difficult.

We attempted to make this determination for Oichnus paraboloides bore holes from the three most abundant species of bored bivalves (Chione elevata, Carditamera floridana and Anadara transversa) from collections at the Caloosa Shell Quarry (Hillsborough County, Florida) of the Pleistocene Fort Thompson and Bermont Formations. Previous research uncovered significant differences in bore hole frequencies on these prey species between the two formations, but the data collected for that research was not useful in determining whether the differences were due to different dominant predators or some other factor. Therefore, we collected new data to allow us to determine whether or not it is likely that two different species were responsible for the other observed variation. We measured the inner and outer bore hole diameter, the distance between the bore hole and the prey's umbo and other morphological variables for several hundred bored specimens and compared the variation within individual species found in the different formations. The results of these analyses will be presented.