First evidence of cannibalism in Crassimurex (s. s.) calcitrapa (Lamarck, 1803) (Gastropoda, Muricidae) from the Lutetian of the Paris Basin (France)

Reports of cannibalistic behavior in fossil muricids are scarce and are only known from the Quaternary. This study presents evidence of cannibalism among Crassimurex (s. s.) calcitrapa (Lamarck, 1803), from the Lutetian of the Paris Basin (France). The studied material comes from the quarry of La Ferme de l’Orme (Yvelines, France) and was collected in a unit (unit 6) in which this species is the lone drilling predator. The paleoenvironment of this bed corresponds to intertidal or shallow subtidal brackish facies and C. (s. s.) calcitrapa is associated with an assemblage containing other euryhaline species. The samples collected include 132 specimens, among which 14 display predatory holes attributed to conspecifics, thus suggesting cannibalism. Small specimens between 2-7 mm are the most commonly drilled and the size of drill holes indicates that juveniles as well as adults are responsible of these attacks. We also observed a global selection of drilling sites that are well oriented to the weak points of the shell (between the varices and avoiding the spines). Finally, this study shows that behaviors such as predation on juveniles, selection of weak parts of the shell and multiple drill holes on the same prey are similar to Quaternary and extant cases. The precise conditions leading to cannibalism are difficult to highlight, but subtidal brackish facies are accompanied by many environmental stressors that can promote opportunistic behaviors such as occasional cannibalism. Also, the sudden appearance of cohorts of hatchlings adds to these stressors.