Piranhas simultaneously replace all the teeth on one side of their mouth

An article published in the journal “Evolution & Development” reports a research on the replacement of teeth in piranhas, the famous carnivorous fish that live in South America’s rivers and lagoons. They, like other species of the Serrasalmidae family commonly known as pacus which are omnivorous, simultaneously replace all the teeth on one side on their mouth. It was a known mechanism but only now it’s been observed and therefore proven.

The name piranha includes not only different species but different genera within the Serrasalminae subfamily that can be omnivorous. In turn, piranhas are part of the Serrasalmidae family together with other genera common in South America’s fresh waters that are predominantly herbivores and are commonly known in those areas as pacus.

To understand the replacement mechanism of piranha and pacu teeth, the researchers coordinated by the University of Washington subjected to CT-scans 93 specimens belonging to 40 different species of fish. The exams allowed to create high-resolution 3D reproductions. Thanks to them, the researchers were able to see the process of replacing existing teeth.

The image (courtesy University of Washington / George Washington University. All rights reserved) shows a CT-scan conducted on a specimen of red-bellied piranha (Pygocentrus nattereri) in which it’s possible to see a row of teeth growing under the already existing ones.

In these groups of fish, the teeth are interlocked together and form two large blocks, each getting replaced in one shot. Matthew Kolmann of George Washington University, who began this research together with Professor Adam Summers, explained that when a tooth wears too much it becomes difficult to replace just one. He compared the group of teeth to an assembly line where teeth work together in a coordinated way and a worn tooth is a weak link.

Probably the interlocked teeth allow to distribute the stress of chewing and replacing them together their consumption is homogeneous. This must be true both for chewing of meat by piranhas and for chewing cellulose fibers by pacus.

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