1. The Jaws of the Piranha
Barry K.B. Berkovitz
Summary
The piranha has a wide reputation for aggression and the sharpness of its teeth. Unusually for fish, they have a limited number of teeth (only six on each side of the upper jaw and seven on each side of the lower jaw) aligned in a row that display a remarkable degree of interlocking to retain stability. Due to the interlocking, it is impossible to shed the teeth individually, as occurs in all other fish where the teeth are also spaced. The piranha has solved this problem in a way unique in the animal kingdom: the teeth on each side of jaw are all shed (exfoliated) at the same time, leaving the fish without any teeth at all in one or more quadrants (quarters) of the jaw. Remarkably, all the teeth in each quadrant are then replaced at the same time and in just a few days. Throughout its life, the piranha undergoes about 27 tooth replacements.