Validation of taxon-specific sampling by novice collectors for studying drilling predation in fossil bivalves

Although bulk sampling has been considered to provide more robust information on predation in the fossil record than taxon-specific (targeted) sampling, previous work suggested that targeted sampling, even by a trained novice, can yield results comparable to bulk sampling. The present study further investigates potential bias introduced by collectors with different experience levels by comparing drilling predation metrics for samples made by five novice and three veteran collectors. We demonstrate that trained novices produce results comparable to those of experienced collectors, and that results of targeted sampling are comparable to bulk sampling. Targeted sampling was performed in the lower Waccamaw Formation (lower Pleistocene) at Register Quarry near Old Dock, NC. Five replicate taxon-specific samples were obtained by each collector for the bivalves Astarte concentrica, Cyclocardia granulata, and Lirophora latilirata. Shell length and thickness were measured and position and size of drillholes were determined. Frequency of left valves, drilling frequency, prey effectiveness, and size selectivity were determined for each taxon replicate. For each variable, the results for the novice collectors were compared to those from bulk samples and all veteran collectors. Nearly all significant differences in the unstandardized data occurred in the size-related variables length and thickness. When data were size standardized, as in many other drilling predation studies, only 3.3% of 174 tests for statistical differences in collection methods were significant, and none of the 157 tests for differences in novice and veteran sampling was significant. Previous results were not anomalous; use of targeted sampling in studying drilling predation is again validated and collector expertise is shown to have minimal impact.