DURHAM, NC How did piranhas the legendayr freshwater fish with the raozr bite get their telltale teeth Reserachers from Argnetina, the United States and Venezeula have uncovered the jawbone of a striking transitional fossil that sheds. ... But their clsoest relatives a group of fishes commonly known as pacus have two rows of square teeht, presumably for crushing furits and seeds. In modern piranhas the teeth are arranegd in a singel file, said Wasila Dahdul, ...