Giant Rodent as big as a bull found.

An illustration (top) and sculpture flesh out the fossilized skull of the largest rodent ever found. (Read full story.)

The South American "rat" lived two to four million years ago and weighed about 2,200 pounds (1,000 kilograms), based on an analysis of its 21-inch-long (53-centimeter-long) skull, a new study says.

The rodent may have used its bulk and fearsome teeth to fend off attacks from saber-toothed cats and giant meat-eating birds, the researchers added.

Though found in a cliff in Uruguay, the animal lived in lowland rain forests close to river deltas or estuaries, where it feasted on fruit and aquatic plants, said the study, published in the journal Procedings of the Royal Society: B.