Meeting Abstract

43.5  Sunday, Jan. 5 11:15  Convergence in morphology and masticatory function between the pharyngeal jaws of grass carp and oral jaws of mammalian herbivores GIDMARK, NJ*; TARRANT, J; BRAINERD, EL; Brown University gidmark@uw.edu

Herbivory is a mechanically difficult dietary specialization, as plant cell walls are chemically inert. In evolutionary shifts to herbivory, many amniotes (especially mammals) have evolved a suite of morphological and functional attributes that aid in mechanical processing of plant material: 1) teeth are flattened to improve grinding performance; 2) teeth are translated laterally in the occlusal plane to impart shearing forces; 3) grinding motions are accomplished with complex 3D jaw kinematics, despite relatively linear tooth kinematics; and 4) motions are highly rhythmic, showing low inter-cycle variability. Here, we explored morphology and in vivo masticatory function in a non-amniote herbivore, the grass carp, Ctenopharyngodon idella. Unlike mammals, the oral jaws are edentulous in grass carp, and all mechanical food processing is accomplished from pharyngeal jaws – modifications of the fifth ceratobranchial in the posterior of the throat. We implanted radiopaque markers into the skull and pharyngeal jaws to track jaw movements using a biplanar x-ray video system. We then used laser scans to register hard-tissue morphology of the jaws to movements of markers tracked on the videos. From these XROMM reconstructions, we demonstrate that the pharyngeal jaws in grass carp grind on the base of the skull, not tooth-on-tooth occlusion. We quantified large lateral translations (nearly 5% of total body length) of flattened tooth cusps that were the result of complex rotations (10-15 degrees) in all three rotational degrees of freedom. Chewing cycles were highly stereotyped: c.v. averaged 12%. These results demonstrate that the suite of morphological and functional characteristics seen in mammalian herbivore specialists has convergently evolved in a cyprinid fish.