Kinematics of the Tongue-Bite Apparatus in Osteoglossomorph Fishes

Osteoglossomorph fishes are characterized by the possession of three sets of jaws used during the capture, maceration and swallowing of prey. One of these jaw systems is a remarkable tongue-bite apparatus used during the intraoral crushing and shredding of prey. Kinematics of the tongue-bite apparatus were quantified, using 200 framess⁻¹ video and film records of feeding in three genera of osteoglossomorph fishes (Osteoglossum, Pantodon and Notopterus) to examine the biomechanics and function of this mechanical system. Two distinct chewing behaviors associated with the tongue-bite apparatus were identified: raking and open-mouth chewing. In all three species, raking behavior involves holding the prey firmly in the mandibular jaws while the teeth of the tongue-bite apparatus are moved into the prey. However, other aspects of raking behavior are significantly different among the species: for example, only Notopterus uses extensive posterior movement of the pectoral girdle to pull basihyal teeth through the prey. In both Osteoglossum and Pantodon there is little motion of the pectoral girdle, and neurocranial elevation plays the major mechanical role in prey reduction, but there are also kinematic differences between Osteoglossum and Pantodon during raking. The kinematics of open-mouth chewing behavior are also significantly different among the three species. Thus, osteoglossomorph fishes share a similar morphology of the tongue-bite apparatus derived from a common ancestor, but have acquired independent kinematic specializations associated with its use.