A comparison of analyses of drilling predation on fossil bivalves: Bulk- vs. taxon-specific sampling and the role of collector experience

Taxon-specific (targeted) sampling, although used in many studies of fossil predator-prey interactions, has been considered to yield less robust predation-related data than bulk sampling. In this study, we tested the utility of taxon-specific sampling by comparing drilling predation data from taxon-specific samples collected by novice and veteran collectors with data from bulk samples collected at the same sites. The bivalves Lirophora latilirata, Astarte concentrica, and Cyclocardia granulata were collected by targeted and bulk sampling from the Lower Pleistocene lower Waccamaw Formation at five localities in southeastern North Carolina. Variables studied included shell length and thickness, left-right valve frequency, drillhole site and prey size selectivity, drilling frequency, and prey effectiveness. Of 139 comparisons, 75% yielded no difference between predation metrics from targeted and bulk samples; most significant differences involved size-related variables. When data were size standardized (as is frequently done in predation studies), 97% of 70 tests showed no difference between the two collecting methods. In addition, when samples collected by novice and veteran collectors were compared, 97% of 214 tests showed no significant differences in predation metrics; the only significant differences involved size-related variables. Results were similar for all three species and across localities. Taxon-specific sampling therefore produces reliable quantitative results for studies of drilling predation, especially when data are standardized by specimen size, and may be superior to bulk sampling when rare or large-bodied taxa are studied.

► We examine two sampling methods commonly used in drilling predation studies. ► Taxon-specific and bulk samples of bivalves yielded comparable predation metrics. ► Targeted samples by novice and veteran collector yielded comparable results. ► Results are most robust when predation data are size-standardized. ► Targeted sampling is a valuable method in research on drilling predation.