Mechanics and Functions of Jaw Protrusion in Teleost Fishes: A Review

Abstract

The more recent and definitive studies on the mechanics and functions of jaw protrusion in teleost fishes are reviewed. Four basic mechanisms characterize the system: In the Type A or depression of jaw protrusion, depression of the mandible pulls or pushes the premaxilla into the protruded state. The force may be transferred to the upper jaw via bones, ligaments or tendons. Twisting of the maxilla around its longitudinal axis may occur passively in this case. The Type B or maxilla utilizes twisting of the maxilla round its longitudinal axis to drive or pull the premaxilla into the protruded position. Twisting of the maxilla is initiated by either depression of the mandible or contraction of the Al division of the adductor mandibulae. In the Type C or decoupled of jaw protrusion the neurocranium is lifted independently from the premaxilla such that the premaxilla is protruded and the Type D or suspensorial abduction augments the latter two mechanisms by abducting the suspensorium to produce tension in the palatopalatine ligament, squeezing the ascending process of the premaxilla such that protrusion of the premaxilla occurs. The first mechanism is shown to be more widespread among the teleosts studied and some of the conclusions concerning the twisting maxilla model are suspect. Previous distinctions among various taxonomic groups based partly on the mechanisms of protrusion are shown to be at least partially incorrect. Hypothesized, and yet untested, functions of jaw protrusion are discussed. Protrusion may either result in a decrease in predation and/or feeding may be energetically more efficient than without it, as a result of a) greater prey capture success with protrusion, b) decreased energy necessary to capture or ingest prey. Lastly, suggestions for the future direction and methodologies of such studies are outlined.