Durophagy in sharks: Feeding mechanics of the hammerhead Sphyrna tiburo

This study investigates the motor pattern and head movements during feeding of a durophagus shark, the bonnethead Sphyrna tiburo, using electromyograp hy and simultaneous high-speed video. Sphyrna tiburo feeds almost exclusive ly on hard-shelled crabs, with shrimp and fish taken occasionally. It captu res crabs by ram feeding, then processes or reduces the prey by crushing it between molariform teeth, finally transporting the prey by suction for swa llowing. The prey-crushing mechanism is distinct from that of ram or bite c apture and suction transport. This crushing mechanism is accomplished by al tering the duration of jaw adductor muscle activity and modifying jaw kinem atics by the addition of a second jaw-closing phase. In crushing events, mo tor activity of the jaw adductor muscles continues (biting of the prey occu rs as the jaws close and continues after the jaws have closed) throughout a second jaw-closing phase, unlike capture and transport events during which motor activity (biting) ceases at jaw closure. Sphyrna tiburo is able to t ake advantage of a resource (hard prey) that is not readily available to mo st sharks by utilizing a suite of durophagous characteristics: molariform t eeth, a modified jaw protrusor muscle, altered jaw adductor activity and mo dified jaw kinematics. Sphyrna tiburo is a specialist feeder on crab prey a s demonstrated by the lack of differences in kinematic or motor patterns wh en offered prey of differing hardness and its apparent lack of ability to m odulate its behavior when feeding on other prey. Functional patterns are al tered and coupled with modifications in dental and jaw morphology to produc e diverse crushing behaviors in elasmobranchs.