May 21, 2008 -- Paleontologists are exchanging finely-chiseled blows over the mightiest rodent to bestride the Earth.
The rat-like beast, dubbed Josephoartigasia monesi, leapt into the headlines in January, when Uruguayan experts said it weighed just over a ton.
Their estimates were based on a massive skull, found on a beach in Uruguay's River Plate region, that was dated to some four million years ago.
The fossil measures 21 inches and boasts gigantic incisors several inches long.
But if Virginie Millien of McGill University, Montreal, is right, J. monesi's estimated mega-size is horribly wrong.
Writing on Wednesday in the British journal Proceedings of the Royal Society B, she says the authors were wrong to try to calculate J. monesi's body mass by drawing a comparison with its closest living relatives, called hystricognath rodents.
According to Millien's calculation's, J. monesi was "certainly the largest rodent ever described" but weighed in at no more than...770 pounds, or about the same as a medium-sized horse.
By comparison, the biggest rodent alive today is the capybara, which can reach 132 pounds.
Despite its terrifying snappers, the creature -- named after Alvaro Mones, a Uruguayan palaeontologist who specialised in South American rodents -- was a peaceable herbivore that slurped on aquatic plants.
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