London (PTI): A rodent the size of a bull? Well, researchers claim to have discovered the remains of the one-tonne beast that thrived in the estuaries and forests of South America four million years ago.

The giant mouse fossil was found in a broken boulder on the coast of Rio de La Plata in Uruguay and studied by Andres Rinderknecht and Ernesto Blanco of Museum of Natural History and Institute of Physics, respectively, in Montevideo.

"We report the discovery of an exceptionally well preserved fossil skull of a new species of rodent, by far the largest ever recorded," the team wrote in the 'Proceedings of the Royal Society, Biological Sciences' journal. "The creature itself weighed between one and 1.4 tons. Its skull is half-a-metre long and reached a length of around three metres, assuming its body was barrel-shaped like that of a capybara.

"The incisors of the mega rodent were around four inches and characteristics of its teeth suggest that it dined on aquatic plants, perhaps even fruit," 'The Daily Telegraph' quoted Dr Blanco as saying.

Rodents are a very successful group of mammals -- accounting for four in every ten species of mammal -- but they are usually small, less than one kg, with the capybara only reaching 60 kg, a lightweight compared with the new find.