Shell repair as a reliable indicator of bivalve predation by shell-wedging gastropods in the fossil record

Shells of the tulip snail Fasciolaria (Cinctura) lilium hunteria often exhibit small (< 1 cm), scallop-shaped repair scars positioned at the convex edge of the apertural lip. When attacking bivalves, Fasciolaria inserts its shell between the preyʹs valves, wedging them apart, which may cause the attacking predatorʹs apertural lip to break. Here, we evaluate whether wedging behavior causes repair scars that are distinct from breakage due to predators such as crabs. Feeding experiments, in which Fasciolaria were offered the oyster Crassostrea virginica, confirmed a wedging-induced origin for the conspicuous band of scars located at the convex apertural lip. These scars occurred regardless of whether the attacks by Fasciolaria on oysters were successful, and they are readily differentiated from scars induced by predatory crabs. Fasciolaria offered to the stone crab Menippe mercenaria and the blue crab Callinectes sapidus suffered extensive damage (embayed breaks typically with a jagged outline). Fasciolaria collected from four localities in southeastern North Carolina exhibited high frequencies of wedging-induced shell repairs, with nearly all shells experiencing evidence of feeding-induced injury. The ability to identify wedging predation traces in the fossil record holds promise for addressing a host of questions related to the role of the behavior in evolution.