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How the Piranha Got Its Teeth

from ScienceNOW Daily News

Piranhas have long been a staple of horror movies, and it's no wonder. Their razor-sharp teeth can tear chunks of flesh from creatures many times their size. Now scientists have rediscovered a fossil piranha jaw that shows how the fish got those choppers.

The closest living relatives of piranhas are pacus, South American river fish that eat mostly plants. ... But pacu teeth aren't nearly as pointy and terrifying as those of the piranha. Another key difference is that pacu teeth are arranged in two rows, whereas piranha teeth are lined up in a single row.

In the 1950s, a scientist proposed that the common ancestor of piranhas and pacus had two rows of teeth, which eventually merged into a single row in piranhas. But nobody had ever seen a fossil showing an intermediate arrangement.