Meeting Abstract

79.5  Sunday, Jan. 6  Preorbitalis and quadratomandibularis function during feeding in little skates, Leucoraja erinacea RAMSAY, J.B.*; WILGA, C.D.; University of Rhode Island jasonramsay@my.uri.edu

The horizontal preorbitalis (PO) muscle of little skates originates from the cranium and inserts onto the lateral surface of the quadratomandibularis (QM) and the lower jaw. The PO is considered to function as a jaw protractor and also may assist the QM in adducting the jaws. However, manual depression of the hyomandibulae and lower jaw results in anteroventral rotation of the PO with little obvious stretching of the muscle as the jaws protrude. Thus, instead of strictly shortening to actuate jaw protrusion and adduction, the PO may potentially contract isometrically or eccentrically; functioning to stabilize and guide the jaws during protrusion driven by hyomandibular depression during the expansive phase of feeding. Hyomandibulae, upper and lower jaw kinematics, as well as motor activity in the PO and QM, and fascicle strain in the PO and QM were recorded simultaneously with buccal pressure during feeding. During prey capture the PO activates isometrically during the expansive phase and continues into the compressive, while the QM actively shortens during the compressive phase. In contrast, during prey processing the PO and QM are passively lengthened during the expansive phase and actively shorten during the compressive phase. The strain patterns exhibited in the PO of little skates suggests that the PO is functioning as an additional suspensory element during rapid prey capture and an additional jaw adductor during prey processing. The dual function of the PO as a supportive and actuating element may be another critical feature resulting in the increased functional versatility of the feeding apparatus in batoids compared to sharks.