chapter  6
38 Pages

Prey Capture Behavior and Feeding Mechanics of Elasmobranchs

ByPhilip J. Motta

CONTENTS 6.1 Introduction .................................................................................................................................. 165 6.2 Ethology of Predation .................................................................................................................. 166

6.2.1 Predatory Behaviors ........................................................................................................ 166 6.2.2 Feeding Location and Prey Capture ............................................................................... 168

6.3 Feeding Mechanism ..................................................................................................................... 171 6.3.1 Mechanics of Prey Capture............................................................................................. 171 6.3.2 Evolution of the Feeding Mechanism............................................................................. 173 6.3.3 Functional Morphology of the Feeding Mechanism...................................................... 174

6.3.3.1 Sharks ............................................................................................................... 174 6.3.3.2 Batoids.............................................................................................................. 183

6.4 Structure and Function of Elasmobranch Teeth .......................................................................... 186 6.4.1 Arrangement and Terminology ....................................................................................... 186 6.4.2 Evolutionary and Functional Patterns............................................................................. 187

6.5 The Enigma of Jaw Protrusion .................................................................................................... 192 6.6 Future Directions.......................................................................................................................... 193 Acknowledgments.................................................................................................................................. 194 References .............................................................................................................................................. 194

6.1 Introduction Perhaps the most remarkable thing about the elasmobranch feeding mechanism is its functional diversity despite its morphological simplicity. Compared to the teleost skull, which has approximately 63 bones (excluding the branchiostegal, circumorbital, and branchial bones), the feeding apparatus of a shark is composed of just 10 cartilaginous elements: the chondrocranium, paired palatoquadrate and Meckel’s cartilages, hyomandibulae, ceratohyals, and a basihyal. Furthermore, the elasmobranchs lack pharyngeal jaws and the ability to further process food by this secondary set of decoupled jaws as do bony fishes. Despite this, sharks, skates, and rays display a diversity of feeding mechanisms and behaviors that, although they do not match those of the bony fishes, is truly remarkable, especially considering there are only approximately 1200 species of elasmobranchs compared to about 24,000 species of teleost fishes (Nelson, 1994; Compagno, 2001). The elasmobranchs capture prey by methods as diverse as ram, biting, suction, and filter feeding, and feed on prey ranging from plankton to marine mammals (Moss, 1972; Frazzetta, 1994; Motta and Wilga, 2001). Understanding the elasmobranch feeding mechanism will shed light on how this functional versatility is achieved and whether or not it parallels that of the bony fishes.