1-ton prehistoric rodent was anything but mousy

LONDON — Imagine a rodent that weighed a ton and was as big as a bull.

Uruguayan scientists say they have uncovered fossil evidence of the biggest species of rodent ever found, one that scurried across wooded areas of South America about 4 million years ago, when the continent was not connected to North America.

An herbivore, the beast may have been a contemporary, and possibly prey, of saber-toothed cats.

The fossil was found in 1987 about 65 miles west of the capital of Montevideo, near the vast River Plate estuary — a muddy waterway separating Uruguay from Argentina that empties into the South Atlantic. That area is site of ancient riverbanks and other deposits where fossils have been found, researcher Ernesto Blanco said.

An Argentine fossil collector identified as Sergio Viera donated the skull to Uruguay's National History and Anthropology Museum nearly two decades ago, said museum director Arturo Toscano.

It spent years hidden away in a box at the museum and was rediscovered by curator Andres Rinderknecht, who enlisted Blanco's help to study it.

The research by Rinderknecht and Blanco was published Wednesday in this week's issue of the biological research journal Proceedings of the Royal Society B.

Its huge skull, more than 20 inches long, suggested a beast more than 8 feet long and weighing between 1,700 and 3,000 pounds.

Although British newspapers variously described it as a mouse or a rat, researchers say the animal, named Josephoartigasia monesi, actually was more closely related to a guinea pig or porcupine.

The extinct rodent clearly outclassed its nearest rival, the Phoberomys, found in Venezuela and estimated to weigh between 880 and 1,500 pounds.

Blanco said the rodent was far more enormous than any South American rodent alive today, surpassing even the present-day capibara that can weigh up to 110 pounds.

"These are totally different from the rats and mice we're accustomed to," said Bruce Patterson, the curator of mammals at the Field Museum in Chicago, adding that it was the biggest rodent he had ever heard of.

The creature may have been a contemporary to the saber-toothed cats and giant carnivorous birds that roamed the area millions of years ago, but Blanco said it was not clear whether such predators had the power necessary to bring down the huge beast.

"I think it's a very important discovery — it is certainly an immense animal," said Mary Dawson, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh.

She said it and other rodents grew bigger by filling the ecological niche taken elsewhere by rhinoceroses and hippopotamuses.

"They got large taking the role of some herbivores that were not present at that time — South America was still an island continent," she said. But when North and South America were linked about 3 million years ago, the rodents were swamped by North American animals and eventually died out.

Little trace of the big rodent is left. Its closest surviving cousin, the pacarana, is endangered. The sharp-clawed 33-pound rodent lives in the hills around the Andes Mountains.

Information from Bloomberg News was used in this report.