Article: Implications for the gastropod fossil record of mistaken crab predation on empty mollusc shells
Sally E. Walker and Sylvia Behrens Yamada
Durophagous crabs were found to make unusually high rates of predatory mistakes by attacking empty gastropods and models of intact bivalves. This mistaken predation is attributed to the crypticity of the shell: if a crab cannot readily determine whether a shell contains food, as is the case with gastropod shells, it will crush it. In contrast, empty bivalve shells (represented by half-shells) are readily examined by crabs and rejected. The taphonomic implications, and importance for the gastropod fossil record, are two-fold. First, where predatory crabs are abundant, shells of gastropods are prone to detrimental biological destruction at three levels: while alive, inhabited by hermit crabs and empty. Bivalves are subject to predation at only one level: while alive. Second, because empty gastropods are preyed upon, peel marks on fossil gastropods are therefore not a reliable indication of crab predation. Mistaken predation is a source of taphonomic bias that needs to be considered in interpreting predation events in fossil gastropods.