Here, we document in-vivo bite forces recorded from wild piranhas. Integrating this empirical data with allometry, bite simulations, and FEA, we have reconstructed the bite capabilities and potential feeding ecology of the extinct giant Miocene piranha, Megapiranha paranensis. An anterior bite force of 320 N from the black piranha, Serrasalmus rhombeus, is the strongest bite force recorded for any bony fish to date. Results indicate M. paranensis' bite force conservatively ranged from 1240-4749 N and reveal its novel dentition was capable of resisting high bite stresses and crushing vertebrate bone. Comparisons of body size-scaled bite forces to other apex predators reveal S. rhombeus and M. paranensis have among the most powerful bites estimated in carnivorous vertebrates. Our results functionally demonstrate the extraordinary bite of serrasalmid piranhas and provide a mechanistic rationale for their predatory dominance among past and present Amazonian ichthyofaunas.