Washington, June 26 (ANI): Researchers from Argentina, the US and Venezuela have uncovered the jawbone of a striking transitional fossil that sheds light on how the ferocious piranhas got their teeth.

Named ‘Megapiranha paranensis’, this previously unknown fossil fish bridges the evolutionary gap between flesh-eating piranhas and their plant-eating cousins.

Present-day piranhas have a single row of triangular teeth, like the blade on a saw, explained the researchers.

But, their closest relatives – a group of fishes commonly known as pacus – 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,” said Dahdul.

Megapiranha shows an intermediate pattern: it’s teeth are arranged in a zig-zag row, which suggests that the two rows in pacus 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 the study.

If this is so, Megapiranha may be an intermediate step in the long process that produced the piranha’s distinctive bite.

To find out where Megapiranha falls in the evolutionary tree for these fishes, Dahdul examined hundreds of specimens of modern piranhas and their relatives.

“What’s cool about this group of fish is their teeth have really distinctive features. A single tooth can tell you a lot about what species it is and what other fishes they’re related to,” said Dahdul.

Her phylogenetic analysis confirms their hunch that Megapiranha seems to fit between piranhas and pacus in the fish family tree.

Cione’s find suggests that Megapiranha lived between 8-10 million years ago in a South American river system known as the Parana.

By comparing the teeth and jaw to the same bones in present-day species, the researchers estimate that Megapiranha was up to 1 meter (3 feet) in length, which is at least four times as long as modern piranhas.

“Although no one is sure what Megapiranha ate, it probably had a diverse diet,” said Cione. (ANI)