Abstract:

Studies on drilling predation in the fossil record often analyze site stereotypy and drilling frequency. Postmortem prey shell breakage can create particular problems for these analyses, especially in high-spired gastropods (e.g., normalizing drill hole location and estimating the number of individuals in a sample). As a result, many previous studies of these taxa have considered only “complete specimens” though “completeness” is rarely well defined, thereby frequently excluding much potential data. We applied two approaches to collect predation data from incomplete shells of Turritella alumensis from the Pliocene Jackson Bluff Formation in Florida. First, we studied site stereotypy using a Theoretical Apex System to normalize drill hole location. Including incomplete specimens revealed a different pattern of site stereotypy than some previous authors have noted: we found two potential populations of drillers acting on different portions of the shells. Second, we calculated drilling frequency by creating a new calculation for normalizing the minimum number of individuals of high-spired gastropods within a sample, making it possible to compare samples with variable amounts of shell breakage. The calculated drilling frequency for shells drilled by larger predators generated using this method was consistent with that calculated using only “complete” specimens. Additional studies are needed to determine whether drilling frequencies calculated using “complete” specimens are always consistent with those generated using the minimum number of individuals method introduced here.

You do not currently have access to this article.