![]() Tooth length scales isometrically with increasing body size (slope = 1.02). Allometric relationship describing growth of the 5 th tooth relative to body size, measured as total length (mm) in the black piranha, S. Homologous landmarks were measured as length of labial base (mm) for the 5 th premaxillary tooth (A). Arrow (inset) demarks fine serrations on M. paranensis share similarly shaped cusps that form labio-lingually compressed triangular blades. paranensis (inset, reprinted from Cione et al.). rhombeus (photo by SH) and fossil teeth of M. ![]() paranensis as sister taxa to the carnivorous “piranha-clade” and a more distant intermediate relative to the herbivorous “pacu-clade” ( SI Fig. These morphological synapomorphies with extant serrasalmid species place M. In contrast, the mid tooth expands into a broad lingual shelf that is anchored to the jaw with a robust circular base ( Fig. They have labio-lingually compressed pointed cusps with finely serrated cutting edges similar to a shark. The fossil teeth are also morphologically distinct. Megapiranha paranensis is classified as a new genus of a giant, piranha-like species described from a single fossilized premaxilla jaw bone fragment that had a set of three triangular teeth set in a zig-zag pattern. 17 described a new extinct serrasalmid species of the Upper Miocene from the Paraná geological formation in Argentina. Dentition and tooth morphology have long been used to classify serrasalmid species 15, 16. Carnivorous piranhas typically have jaws lined with a single row of 6–7 serrated, multi-cusped, triangular, blade-like teeth. Tooth shape and dentition patterns in Serrasalmidae demonstrate a strong functional relationship to diet 11, 12, 13. Within the piranha-clade, feeding ecology varies from the typical flesh and fin eating forms of Serrasalmus and Pygocentrus spp., to the highly specialized lepidophagous (i.e. Recent molecular evidence indicates there are three major subclades of the Serrasalmidae: 1) the carnivorous piranha-clade, 2) the omnivorous Myleus-clade and 3) the herbivorous pacu-clade 14. Even at their small body sizes, diet studies indicate that piranhas will attack and bite chunks out of prey many times larger than themselves 11, 12, 13. While anecdotes of piranha-infested waters skeletonizing hapless victims are generally hyperbole, the effectiveness of their bite is not. Among bony fishes, piranhas (Serrasalmidae) represent an ideal group of predatory vertebrates in which to investigate the evolution of extreme biting capabilities because of their aggressive nature, relatively small size and accessible populations. In-vivo experiments in the field to elicit and record ecologically realistic biting behaviors for predatory species are rare, dangerous and difficult to perform 10. ![]() However, few theoretical studies have validated their models with empirical measurements from living taxa 7, 8, 9. ![]() As a result of their fundamental importance in expanding predatory niches and promoting the success of vertebrates, jaws and bite forces in living and extinct species have been repeatedly modeled through lever and linkage mechanics, bite simulations and 3-D finite element analyses (FEA) 2, 3, 4, 5, 6. The evolution of gnathostome jaws, along with bite forces that can capture and masticate active prey is a key functional innovation underlying the diversification of early Devonian vertebrates 1. ![]()
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