January 2025 Bulletin

Reverse drill holes: remarkable mistakes made by gastropod predators attacking Neogene bivalve prey Adiël A. Klompmaker1* and Gregory P. Dietl2,3 1 Department of Museum Research and Collections and Alabama Museum of Natural History, University of Alabama, Box 870340, Tuscaloosa, Alabama 35487, USA 2 Paleontological Research Institution, 1259 Trumansburg Road, Ithaca, New York 14850, USA 3 Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA Non-technical Summary.—Predators regularly attack their prey unsuccessfully, but the cause of failure is often difficult to determine in the fossil record. We report on drill holes in the shells of two Neogene bivalves from the Netherlands in which the drilling gastropod predators did not make effective use of their sensory capabilities to distinguish dead from live prey. These holes, which we call reverse drill holes, were produced from the inner side of the bivalve prey’s shell. [clearer language]. We propose that chemical cues from live prey directly around the dead shell stimulated the gastropods to make these mistakes. Hunger is another hypothesis for reverse drilling behavior. These holes are the earliest docu mented instances of reverse gastropod drill holes in the fossil record. In the two assemblages examined, reverse drill holes are rare, accounting for less than 1% of all drill holes, in contrast to other forms of unsuccessful predation, such as incomplete drill holes and multiply-drilled specimens. This finding suggests that the predator’s sensory and decision making processes were typically effective at differentiating between live and dead prey. Abstract.—Predation is a behavior that is commonly unsuccessful, but the cause of failure is often difficult to determine in the fossil record. Here, we report on gastropod drill holes in two Plio- and Miocene bivalve specimens from the Neth erlands created from the inner side of the bivalve prey’s shell, which we call reverse drill holes. These holes are unequiv ocally caused by failure of the gastropod drilling predators to make effective use of their chemoreception and mechanore ception sensory adaptations. We hypothesize that the diffuse nature of chemical cues emanating from dense aggregations of living prey could have confused foraging predators and stimulated them to initiate the drilling process on empty valves. Poor decision making due to hunger is an alternative hypothesis. These traces represent the first reported exam ples of reverse gastropod drill holes from the fossil record, and the first attributed to Naticidae. Compared to other types of failed predation (incomplete drill holes and drill holes in multiply-drilled specimens) in the two assemblages studied, reverse drill holes are rare (< 1% of drill holes). This result implies that the driller’s sensory and decision-making processes were generally reliable at distinguishing dead from live prey.