Evidence of Cheliped Autotomy and Regeneration in the Lower Miocene Crab Achelous monspeliensis From Portugal

Autotomy—the voluntary shedding of a limb as a defensive response to predation, intraspecific aggression, or infection—followed by regeneration during subsequent molting is a common behavior among decapod crustaceans. In the fossil record, however, evidence of this behavior is typically indirect and difficult to verify. In this study, we report compelling cases of autotomy, in at least one case followed by limb regeneration in Achelous monspeliensis from the Burdigalian deposits of Bicas–Foz da Fonte coastal section (Lower Miocene, Portugal). We based our analysis on one of the best collections of this crab species presently available for study. Among some specimens preserving pathological evidences, two crabs belonging to this homochelate species exhibit partial regeneration of cheliped characterized by marked dimensional asymmetry of the podomeres. The aborted regenerative sequence indicates that they died before completing the number of molts required to fully restore the limb to its original size.