Epibulus insidiator (Pallas) possesses the most extreme jaw protrusion ever measured in fishes. Biomechanical models of the mechanisms of jaw protrusion and hyoid depression in Epibulus are proposed and tested. The models are designed using principles of four-bar linkages from engineering theory. The models calculate the geometry of the feeding mechanisms from morphometric data on cranial anatomy. Predictions made from the models about the feeding kinematics of Epibulus are tested by comparison with kinematic data. The model of the jaw mechanism is accurate in predicting the unique feeding mechanics of the jaws of Epibulus for most relationships between kinematic variables. A model of simultaneous cranial elevation and sternohyoideus muscle contraction is accurate in predicting hyoid depression during feeding. Biomechanical considerations limit the number of possible pathways of evolution of the jaw mechanism of Epibulus from that of its closest labrid relatives.

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