Attempts to predate on gadid fish otoliths demonstrated by naticid gastropod drill holes from the Neogene of Mill-Langenboom, The Netherlands

Incomplete drill holes produced by naticid snails are occasionally found in late Cenozoic gadid otoliths from the North Sea Basin. Among the Neogene otoliths found at Mill-Langenboom naticid drill holes are relatively common. Their occurrence is linked to strata that formed under reduced rates of sedimentation and/or that reflect non-sedimentation and erosion. The Upper Miocene–Upper Pliocene deposits at Mill-Langenboom (province of Noord-Brabant, the Netherlands) constitute a condensed sequence comprising most North Sea Basin stages of this interval from the Gramian to the end of the Pliocene, as demonstrated by index taxa amongst gadid otoliths, with a considerable hiatus between Miocene and Pliocene strata. The lag deposit at the base of the Pliocene yields otoliths that were reworked from eroded Upper Miocene, and Lower and Middle Pliocene sedimentary rocks. Smaller hiatuses exist within the Pliocene. Under such conditions, isolated otoliths can occur in sufficient numbers on the sea floor or just below it, where naticids live and search for prey. The drill holes occur exclusively in otoliths of relatively small, locally abundant extinct species of cod. Most of these otoliths originate from individuals that must have been eaten by larger predators. Overall otolith shape more or less resembles the shell of tellinid bivalves. It is evident that the naticids have become aware of their mistake prior to finishing their drilling, because drilling never exceeded depths more than half the otolith thickness. This is the first published record of drill holes in otoliths.