A newly discovered fossil of a previously unknown species of piranha, dubbed "megapiranha" (scary!) is being examined as the step between modern piranhas and a related, much larger species called pacu. The megapiranha is 3-foot in length (again, scary!) and holds clues in the formation of its teeth. From MSNBC:Present-day piranhas have a single row of triangular teeth, like the blade on a saw, explained the researchers. Pacu have two rows of square teeth, presumably for crushing fruits and seeds."In modern piranhas, the teeth are arranged in a single file," said Wasila Dahdul, a visiting scientist at the National Evolutionary Synthesis Center in North Carolina. "But in the relatives of piranhas — which tend to be herbivorous fishes — the teeth are in two rows."
The new fossil shows an intermediate pattern: teeth in a zig-zag row. This suggests that the two rows in pacu were compressed to form a single row in piranhas. "It almost looks like the teeth are migrating from the second row into the first row," said John Lundberg, curator at the Academy of Natural Sciences in Philadelphia and a co-author of a study of the jawbone.
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