Meeting Abstract
Carnivorous piranhas and herbivorous pacus have curious dentitions for teleosts; many species show some degree of heterodonty attributed to adaptations for either carnivorous or herbivorous diets, respectively. Tooth replacement in piranhas is also unusual – all the teeth on one side of the head are lost as a unit, then replaced simultaneously. Moreover, the arrangement and shape of teeth in serrasalmids is a principal means of distinguishing between many genera. We used CT scanning and histology to examine tooth replacement across serrasalmids, and map replacement characters onto a molecular phylogeny. Pacu teeth develop and are replaced in a manner similar to piranhas. All serrasalmids (with one notable exception) share a unilateral tooth replacement pattern, so this is not an adaptation for carnivory. However, this unilateral replacement mode is not an ‘all or nothing’ phenomenon – we present evidence that both sides of the jaws have developing tooth rows within them, albeit one is more mineralized than the other. These patterns are found to be consistent over ontogeny in size series of the piranha Pygocentrus and the pacu Metynnis. Additionally, both pacus and piranhas use accessory tooth cusps to interlock adjacent teeth together, forming dental batteries. We propose that this interlocking mechanism (and perhaps heterodonty) begets simultaneous replacement and ensures that functionality of the feeding apparatus is not interrupted by tooth loss, as might occur in other instances of polyphyodont tooth replacement. Finally, we propose that this mode of simultaneous replacement be considered as a synapomorphy for the family.
