How do elasmobranchs crush hard prey with a “soft” skeleton?

Until recently biologists had wondered how an animal with a cartilaginous skeleton could crush the hard shells of marine molluscs such as bivalves (e.g. mussels, clams, oysters, cockles, etc.). Studies by Adam Summers at the University of California at Irvine’s Ecology and Evolutionary Biology Department have, however, shed some light on this conundrum. Summers’ studies on the feeding mechanisms of the spotted eagle ray (Aetobatis narinari), a large tropical ray that feeds on clams, oysters and snails amongst other things, have revealed that these elasmobranchs have evolved calcified struts that run right through the jaws to support the crushing plates. Interestingly, the same struts aren't employed by sharks. It seems that in the horn shark (Heterodontus francisci), a medium-sized tropical and subtropical shark that feeds on sea urchins, crabs, worms, anemones and bony fishes, the shape of the jaws provide the support for their crushing plates.