75.3 Sunday, Jan. 6 Role of the kinethmoid in jaw protrusion of common carp, Cyprinus carpio GIDMARK, NJ*; STAAB, KL; HERNANDEZ, LP; BRAINERD, EL; Brown University; George Washington University; George Washington University; Brown University email@example.com
Jaw protrusion is an important component of the food acquisition system in most fishes, and various mechanisms for jaw protrusion have evolved independently. The most widely studied mechanism is the 4-bar linkage in labroid fishes, in which lower jaw depression causes rotation and ventral translation in the maxilla and forward protrusion in the premaxilla. The ancestral mechanism for chondrichthyan jaw protrusion involves an anterior pulling of the posterior portion of the upper jaw, resulting in protrusion and ventral translation of the jaw. Sturgeons use rotation of the hyomandibula which pushes the symplectic anteriorly, and in turn protrudes both the upper and lower jaws. Jaw protrusion has not been thoroughly studied in cypriniform fishes, however, despite the impressive diversity of this group. Cypriniforms are particularly interesting because they possess a novel bone, the kinethmoid, which is thought to contribute to jaw protrusion. The kinethmoid is a midline, sesamoid bone that develops within the tendon running from the premaxilla to the neurocranium. We used high-speed cinefluoroscopy coupled with anatomical modeling to study skull element movement in common carp, Cyprinus carpio. We find that for maximum premaxillary protrusion, the kinethmoid rotates about the maxillae, pushing the premaxilla forward. In instances where the jaws must open but extensive premaxillary protrusion is not necessary, such as breathing, the kinethmoid does not rotate. Instead, it remains in its retracted position, holding the dorsal edge of the premaxilla in place while the ventral process of the premaxilla rotates anteriorly. This mechanism could serve as a method of modulating the suction force induced during different jaw opening behaviors, such as feeding and respiration.