Caedichnus, a New Ichnogenus Representing Predatory Attack on the Gastropod Shell Aperture

Abstract

Predatory traces, in which the tracemaker has damaged the prey animal's skeleton to kill and consume it, have a deep fossil history and have received much scientific attention. Several types of predatory traces have been assigned to ichnotaxa, but one of the most studied predatory traces, the wedge-shaped excision produced as a result of attacks mainly by crustaceans on the apertures of gastropod shells, has yet to be described as an ichnotaxon. We propose the ichnogenus Caedichnus to describe the shell damage produced by aperture peeling behavior. Caedichnus is produced by predators that are unable to crush their prey's shells outright. Depending on the predator's peeling ability and the prey's withdrawal depth within the shell, the trace can extend through several whorls of the shell. Aperture peel attacks may fail, allowing such damage to be repaired by surviving gastropods. Thus, the types of attacks that produce Caedichnus may exert selective pressure on prey to evolve better-defended shells (in the case of gastropods) or to inhabit better-defended shells (in the case of hermit crabs). The identification of these trace fossils will enhance our understanding of how predation influences the morphological, and even behavioral, evolution of prey organisms.

Keywords:

• Durophagy
• Shell peeling
• Decapoda
• Hermit crab
• Trace fossil

ACKNOWLEDGMENTS

We thank P.H. Kelley and M.G. Simoes for their insightful and constructive reviews of the manuscript. Yan Li photographed the type and example specimens. A.R. Palmer, G.J. Vermeij, and G.A. Sanchez-Azofeifa gave feedback on a version of this manuscript. F.L. Forcino assisted with an early version of the manuscript.

FUNDING

Funding came from an NSERC Discovery Grant and a National Geographic Exploration Grant to Leighton. Stafford received funds from the American Museum of Natural History Lerner-Gray Fund for Marine Research, a Paleontological Society Ellis L. Yochelson Student Research Award, a Conchologists of America Academic Grant, and a Geological Society of America Student Research Grant.