Meeting Abstract
The serrasalmid fishes, pacus and piranhas, exhibit considerable dietary diversity, feeding on fins, scales, and whole fishes to the seeds, fruits, and leaves of aquatic and terrestrial plants. These prey span both an ecological and a biomaterials continuum, from tough plant fibers and silicated matrices to the chitin, muscle, bone, and sinew of animal prey. Serrasalmids feed on such prey using jaws with only a few degrees of freedom; essentially the jaws are constrained to only dorso-ventral abduction/adduction. Compared to other bony fishes, serrasalmids have fused most of their cranial skeleton together, resulting in an akinetic skull with with little obvious proclivity for jaw protrusion. How can such a ‘simple’ skeletal arrangement result in such dietary diversity? We describe the gross anatomy of the feeding morphology and infer functional themes across the serrasalmid fishes using both manual dissection and contrast-enhanced μCT scanning. We document hidden myological complexity in serrasalmids, stemming in particular from the divergence in lever mechanics between herbivorous pacus and carnivorous piranhas. Piranhas in particular seem constrained in cranial space, jaw adductors appear to have displaced branchial musculature posteriorly. Pacus and piranhas feature different arrangements, fiber architecture, and hypertrophy of select adductor mandibulae divisions, we suspect as a means of augmenting jaw leverage for different occlusal regimes. These occlusal modes presumably relate to gape limitation incurred by different prey: granivorous and frugivorous pacus feed on large, ovoid prey items while piranhas are frequently gouging chunks of flesh, fins, or scales from prey.
