IS CRUSHING A-PEEL-ING? CHARACTERIZING PREDATORY SHELL BREAKING SHAPES USING 2D GEOMETRIC MORPHOMETRICS

Trace fossils provide evidence of the behaviors and interactions of organisms throughout Earth’s history. Shell breaking is a type of predation on mollusks, typically carried out by fishes or decapods. However, shell breakage can result from predation or abiotic factors. To characterize breakage shapes left on prey, we examined damage induced by two modern shell-breaking predators, the flame-streaked box crab (Calappa flammea), which peels gastropod shells, and the stone crab (Menippe mercenaria), which crushes them. We compared the breakage traces made by the two crab species on modern gastropods to those found on Devonian fossil gastropods, using a combination of qualitative observations and 2D geometric morphometric analyses. Preliminary geometric morphometric analysis of breaks in modern gastropod shells could not distinguish between the two breakage types from the live crabs by its shape, but breakage traces on fossil shells fell centrally within the convex hulls of both the crushing and peeling shapes in modern gastropods, supporting the claim that they may have been made by predators. In addition, preliminary angular morphometric data suggest that peeled shells have larger and more variable breakage angles (rotating significantly farther around the shell as a result of successful breakage) than crushed shells. Thus, the extent to which a break rotates around the shell may help to determine the predation method responsible for particular traces on fossil gastropods if the fossils have the same breakage rotation.