Marine Pliocene mollusks are abundant in sand deposits at Langenboom, the Netherlands. Three samples, totaling nearly 15,000 mollusks, were identified and assessed for drill-hole predation marks. An approach commonly used by researchers was performed to calculate a drill-hole predation intensity based on bivalves with complete margins only. This method, however, introduced a significant taphonomic bias: an assemblage of bivalve drill-hole predation intensity of ∼30% was found for complete valves only, compared to an assemblage of bivalve drill-hole predation intensity of ∼20% based on complete and fragmented valves with more than 50% of the hinge preserved. This bias was caused by a significant change in the faunal composition when fragmented valves, primarily broken by compaction, were taken into account. For assemblages with many broken valves, this bias should be estimated to be comparable to drill-hole predation intensities based on pristine collections. This bias becomes especially important in studies on evolutionary escalation through time. Naticids appeared to be the predominant drill-hole-producing predator (only one definite drill hole was found) based on drill-hole morphology and the gastropod composition. Muricid predators were absent, probably because most bivalve prey is infaunal.

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