PREDATORY EFFICIENCY: AN EXPERIMENTAL TEST OF SHELL BREAKING IN CRABS USING PEELING VERSUS WHOLE-BODY CRUSHING MECHANISMS

The destructive nature of durophagy biases the fossil record towards evidence of predator failure rather than success. Hence, much of our understanding of the evolution of durophagous interactions comes from healed repair scars on mollusks after a failed attack. This bias makes it difficult to analyze hundreds of millions of years of predator-prey interactions using fossils alone. In the case of predators such as crabs, where the preservation potential of predatory morphologies (e.g., claws) is heavily impacted by taphonomy, conducting experiments using modern analogues is crucial. One example of these predators is durophagous crabs such as Calappa, which have a unique tubercle on the dactyl of the dominant claw, first evident in Cretaceous species, enabling them to peel shells in a manner often referred to as “can opening”. We conducted live feeding experiments comparing the capabilities of the peeling crab Calappa flammea with the whole-body crushing crab Menippe mercenaria in order to explore how the morphology of shell peeling claws influences predatory efficiency. C. flammea and M. mercenaria were fed gastropods and bivalves. In addition to observing differences in prey manipulation techniques we found that C. flammea induced shell breakage in gastropods significantly faster than M. mercenaria. In contrast, both species took a similar time to initiate breakage in bivalves. Our results demonstrate that specific adaptations which evolved by the Cretaceous enhanced the predatory efficiency of crabs by increasing breakage speed and reducing prey size limitations when peeling gastropod shells rather than crushing them whole.