Feeding Mechanisms in Sharks

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Abstract
Although many sharks have a rather general vertebrate body plan, they display a number of specializations for feeding that belie the notion that they are “primitive.” These specializations include a battery of highly developed exteroceptive systems such as vision, olfaction, acoustico-lateralis sense and electroreception; and a cranial morphology that has been molded into a number of functionally adaptive forms. These forms result in grasping, sucking, crushing, gouging, cutting and filtering systems of feeding. With relatively few exceptions elasmobranch feeding mechanisms share such features as subterminal or inferior mouths, a dynamic tooth replacement system, hyostylic jaw suspension and a kinetic, protractile upper jaw. The importance of each of these components is discussed. The evolution of the high diversity of mechanical feeding systems in such a small group of vertebrates has probably been facilitated by the morphological simplicity of the basic feeding mechanism. This radiation was accomplished by modifications in jaw length, the length and supporting angle of the hyomandibula, the size of the gape, dentition and changes in the relative size of the cranial musculature. The evolutionary pattern of shark feeding mechanisms is complex, there being several examples of both parallelism and convergence. A long-jawed, grasping form (similar to, but not identical with Chlamydoselachus) is here considered primitive. From a subsequent benthic sucking and grasping ancestor, similar in many respects to some living batoids,radiated crushing, ray-like forms; cutting, squaloid forms; and gouging, lamniform and carcharhiniform types. From the latter developed sucking and grasping, or crushing forms such as modern orectolobiforms, triakids and heterodontiform sharks. From several levels (primary crushing, secondary crushing and gouging) there emerged filter-feeding forms represented today by mobulids, rhiniodontids and cetorhin.

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