Yard-long "Megapiranha" Fossil Found
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Eight to ten million years ago, South America's waters harbored a toothier, three-foot (one-meter) version of today's famed, flesh-eating piranhas.Alberto Cione, a paleontologist at Argentina's La Plata Museum, first noticed the evidence of Megapiranha pananensis (pictured in an artist's rendering)--an upper jaw with three unusually large and pointed teeth--in his collection in the 1980s. The remains had been discovered half a century earlier in a riverside cliff in northeastern Argentina.
Cione and his colleagues now report that Megapiranha bridges the evolutionary gap between modern-day piranhas and plant-eating pacu fish. The new study appears in the June 2009 issue of the Journal of Vertebrate Paleontology.
In modern piranhas, teeth are arranged single file, whereas related, plant-eating pacus have two rows. This three-inch (eight-centimeter) fossil jaw fragment from a Megapiranha shows a zigzagging tooth arrangement--an evolutionary midpoint between the pacu and piranha patterns, experts announced in a June 2009 study.
At least one mystery remains, however.
"The fossils have seven teeth and [modern] piranhas have six," said study co-author Wasila Dahdul, an evolutionary biologist at the University of South Dakota. Did the seventh tooth "just get completely lost over time, or maybe two teeth fused? That's something we don't know."
Despite their fearsome reputation, modern piranhas are usually no longer than a foot (30 centimeters) and only occasionally bite humans. More often, they annoy fishers by attacking the anglers' catches--even if the catch is another piranha.
As for Megapiranha, no one is sure what it ate, but scientists suspect it had a diverse diet.
"It's probably not something we can reconstruct at this point," biologist Wasila Dahdul said.
credited to news.nationalgeographic.com
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