Piranha swap out their old teeth with new set waiting in a 'crypt'

A CT-scanned image of the piranha Serrasalmus elongatus, also known as elongated or pike piranha. Note the ingested fish fins in its stomach.

(CNN)Piranha teeth have the tough task of crunching bone and shredding flesh and, like well-used kitchen knives, they dull over time. Since they have no way to sharpen their teeth, piranhas lose and regrow all of the teeth on one side several times over their lifespan.

A new analysis of piranha teeth revealed that a new set of teeth wait in a "crypt" below the current teeth so that the fish are never without a pair. This way, they can happily keep munching on what the study refers to as an "anatomical potpourri of fish parts, ranging from scales and fin rays, chunks of flesh and whole fishes."
The study published in the journal Evolution and Development.
    Previous research showed that piranhas lose one row of teeth at a time and replace them with sharp new ones. But scientists didn't find any examples of piranhas missing teeth.
    But piranhas aren't the only fish that experience this. They have plant-eating relatives called pacus that lose an