Serrasalmidae

Serrasalmidae is the family of piranhas. All are native to South America. It includes several extant genera like "Serrasalmus", and an extinct genus called "Megapiranha". These fish are quite scary because they eat humans. 
Description.
Piranhas have sharp teeth, meaning that they can injure humans. A pycnodont called "Piranhamesodon" has teeth resembling a piranha. If you've seen a real "Piranhamesodon", it would eat you alive. An extant fish called the bluefish is called the marine piranha because of its teeth.