Taphonomic significance of hermit crabs (Anomura: Paguridea): Epifaunal hermit crab — Infaunal gastropod example

Abstract

As secondary inhabitants of gastropod shells, hermit crabs (Anomura: Paguridea) can influence the preservation potential and resulting fossil record of gastropod shells and can modify the paleoecological information left on the shells. The fossil record of hermit crabs is almost non-existent (occasional chelipeds) and does not illuminate the role of hermit crabs as taphonomic agents. However, observations and experiments on bionts associated with modern hermit crab-inhabited gastropod shells demostrate a series of specific criteria by which bionts can be used to infer the presence of pagurids in the fossil record, their behavior, and the taphonomic consequences for the gastropod record since the origin of Paguridea in the Early Jurassic. This study shows that the infaunal snail shell, Olivella biplicata, when occupied by the epifaunal hermit crab, Pagurus granosimanus, has a unique set of filter-feeding bionts present in the aperture region of the shell. These bionts are not found on the living snail, do not settle on experimental tethered shells, and, because they leave bore holes or etchings on the shells, provide trace fossil evidence of hermit crab occupation of fossil shells. The taphonomic experiments revealed that empty tethered shells are more likely to be crushed by predators than buried. Experiments on the burial of previously hermitted shells show that some bionts are more likely to be destroyed early in the burial history (e.g., barnacles) than others (e.g., encrusting bryozoa).