Meeting Abstract
Potamotrygon motoro, a freshwater stingray from the Amazon river, is thought to process insect prey with asymmetric, shearing jaw motions characteristic of mammalian masticators. However, the cartilaginous elements of the batoid feeding apparatus (chondrocranium, hyomandibulae, Meckel’s cartilage, palatoquadrate) are obscured by several layers of tissue and difficult to visualize with standard video cameras. Accordingly, we used marker-based XROMM (X-ray Reconstruction of Moving Morphology) to visualize and measure the motions of P. motoro’s cranial cartilages during processing. We find that P. motoro utilizes two kinematically distinct types of chew cycles to break down tough prey. In addition to standard compressive chews, P. motoro occasionally performs exaggerated chews we term overbite (OB) cycles. In OB cycles, the upper jaw rotates past regular occlusion, shearing the prey along the curved lower jaw tooth plate in a manner similar to the propalinal chewing observed in some mammals. OB cycles are facilitated by extremely flexible jaw symphyses and what appears to be independently controlled upper and lower jaw depression. Also, we find variable asymmetry in the magnitude of left and right jaw joint rotation, as well as in whole-jaw deviation from midline during protrusion. The latter is made possible, in part, by the additional degrees of translational freedom provided by the angular cartilages.
