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The nurse shark, Ginglymostoma cirratum, is an obligate suction feeder that preys on benthic invertebrates and fish. Its cranial morphology exhibits a suite of structural and functional modifications that facilitate this mode of prey capture. During suction-feeding, subambient pressure is generated by the ventral expansion of the hyoid apparatus and the floor of its buccopharyngeal cavity. As in suction-feeding bony fishes, the nurse shark exhibits expansive, compressive, and recovery kinematic phases that produce posterior-directed water flow through the buccopharyngeal cavity. However, there is generally neither a preparatory phase nor cranial elevation. Suction is generated by the rapid depression of the buccopharyngeal floor by the coracoarcualis, coracohyoideus, and coracobranchiales muscles. Because the hyoid arch of G. cirratum is loosely connected to the mandible, contraction of the rectus cervicis muscle group can greatly depress the floor of the buccopharyngeal cavity below the depressed mandible, resulting in large volumetric expansion. Suction pressures in the nurse shark vary greatly, but include the greatest subambient pressures reported for an aquatic-feeding vertebrate. Maximum suction pressure does not appear to be related to shark size, but is correlated with the rate of buccopharyngeal expansion. As in suction-feeding bony fishes, suction in the nurse shark is only effective within approximately 3 cm in front of the mouth. The foraging behavior of this shark is most likely constrained to ambushing or stalking due to the exponential decay of effective suction in front of the mouth. Prey capture may be facilitated by foraging within reef confines and close to the substrate, which can enhance the effective suction distance, or by foraging at night when it can more closely approach prey.

Bite force, a measure of performance, can be used to link anatomical form and function. Earlier studies have shown bite force to have a significant influence on dietary constraints and ontogenetic shifts in resource utilization. The bonnethead shark, Sphyrna tiburo, is a durophagous member of the family Sphyrnidae. Its diet in South Florida waters consists almost entirely of blue crabs, which are crushed or ingested whole. This abundant coastal predator's feeding mechanism is specialized for the consumption of hard prey, including a modified biting pattern and molariform teeth. The goals of this research were to (1) characterize the mechanical function of the feeding mechanism of S. tiburo through biomechanical modeling of biting and in vivo bite force measurements; (2) compare the bite force of S. tiburo with those of other fishes; and (3) identify functional constraints on prey capture by comparing the bite force of S. tiburo with the fracture properties of its primary prey item, blue crabs. Maximum theoretical bite force ranged from 25.7 N anteriorly to 107.9 N posteriorly. S. tiburo has the second lowest mass specific bite force for any fish studied to date, and its posterior mechanical advantage of 0.88 is lower than other durophagous chondrichthyans, indicating that this independent evolutionary acquisition of durophagy was not accompanied by the associated morphological changes found in other durophagous cartilaginous fishes. Blue crab fracture forces (30.0-490.0 N) range well above the maximum bite force of S. tiburo, suggesting that prey material properties functionally constrain dietary ecology to some degree.

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