Abstract

A major caveat of using gastropod drill holes to assess predator-prey interactions in modern and ancient ecosystems is identification of holes produced by predation versus other means. A recent method to confirm the predatory origin of holes uses Radulichnus-like microtraces left within the drill hole from the physical rasping of prey shell material, but the utility of these microtraces to assess biological information from the drilling predator has not been investigated. Generating artificial rasp marks using extracted radulae and producing drill holes by artificial means offered insights into the mechanical factors influencing microtrace morphology. Controlled laboratory feeding trials provided prey shells with drill holes of known origins, and corresponding gastropod predator radulae (Nucella lamellosa, Muricidae). These prey shell–predator radula pairs were analyzed under environmental scanning electron microscopy (ESEM) to comparatively assess spacing of radula intercusps and drilling microtraces. Artificial replication of microtraces using focused ion beam scanning electron microscope (FIB-SEM) micromanipulation demonstrates that microtraces provide reasonable approximations of radula dentition size and morphology. Depending on mechanical inconsistencies of the drilling process, however, microtrace expression may vary within and across individuals. Microtrace spacing parallels radula intercusp spacing (r  =  0.50; p  =  0.03), but no correlation was observed between intercusp spacing and predator size, which suggests that microtraces cannot serve as a proxy for predator size. With morphological conservation of the radula expressed in the microtraces, however, further investigation of microtraces may bolster the correct identification of predatory traces and afford insights into the identity of the drilling predator in the fossil record.

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