Kinematic Analysis of Suction Feeding in the Nurse Shark, Ginglymostoma cirratum (Orectolobiformes, Ginglymostomatidae)

Abstract

Inertial suction feeding is known to occur in some sharks, but the sequence and temporal kinematics of head and jaw movements have not been defined. We investigated the feeding kinematics of a suction feeding shark, the nurse shark Ginglymostoma cirratum, to test for differences in the timing and magnitude of feeding components with other shark taxa when sharks were fed pieces of bony fish. Thirteen kinematic variables were measured from high-speed video recordings. Food capture in this species consists of expansive, compressive, and recovery phases, as in most other sharks, but there is little or no cranial elevation. Mean time to maximum gape (32 msec) is the fastest recorded for an elasmobranch fish. Other relatively rapid events include mandibular depression (26 msec), elevation (66 msec), and total bite time (100 msec). Buccal valves assist the unidirectional flow of water into the mouth and out of the gill chambers. Food capture under these experimental conditions appears to be a stereotyped modal action pattern but with significant interindividual variability in timing of kinematic events. Ginglymostoma cirratum exhibits a suite of specializations for inertial suction feeding that include (1) the formation of a small, anteriorly directed mouth that is approximately round and laterally enclosed by modified labial cartilages; (2) small teeth; (3) buccal valves to prevent the backflow of water; and (4) extremely rapid buccal expansion. Sharks that capture food by inertial suction have faster and more stereotyped capture behavior than sharks that primarily ram feed. Inertial suction feeding, which has evolved multiple times in sharks, represents an example of functional convergence with inertial suction feeding bony fishes.