One ton rodent

Scientists in Uruguay have found the fossil remains of a 1 tonne rodent that lived 2 million to 4 million years ago – the largest rodent ever found.

The giant creature probably ate soft food such as fruit or tender plants, Andres Rinderknecht and Ernesto Blanco of the National Museum of Natural History in Montevideo reported on Wednesday.

"We report the discovery of an exceptionally well preserved fossil skull of a new species of rodent, by far the largest ever recorded," they wrote in a report in Britain's Proceedings of the Royal Society.

"Rodents are a very successful group of mammals living almost worldwide and with small body masses (generally less than 1 kg or 2.2 pounds)," they wrote.

"However, our work suggests that 4 million years ago in South America, rodents with 1 tonne of body mass (a 'mouse' larger than a bull) lived with terror birds, saber-toothed cats, ground sloths and giant armoured mammals among others."

They have named the fossil Josephoartigasia monesi. They dug it out of rock along the Rio Plata and said they were amazed at its size.

But it had small teeth and weak jawbones.

"These features suggest that J. monesi had weak masticatory muscles for grinding food and probably did not have the abrasive diet typical of other (similar) rodents," they wrote.

"Palaeobiologically this could imply a diet composed of soft vegetation and perhaps fruit."

The largest living rodent is the carpincho or capybara found in parts of South America. They can grow to about 60 kg(132lbs).