The prehistoric, bull size creature, the world's largest recorded rodent has been identified from a well preserved skull in South America. The megarodent lived in lowland rain forests between two and four million years ago, perhaps using its massive teeth to fend off saber-toothed cats and giant, flightless, meat-eating birds, researchers say. The rodent weighed about 2,200 pounds (1,000 kilograms), based on an analysis of its 21 inch long (53 centimeter long) skull. The skull suggests that the species was twice as heavy as any other known rodent. A relative of rats, mice, and guinea pigs, the creature measures some ten feet (three meters) long, nose to tail. The ancient animal lookes a lot like the capybara, the world's largest living rodent, also from South America. The prehistoric mammal belonged to a rodent family with a single surviving member, the pacarana. A rare species weighing up to 33 pounds (15 kilograms), the pacarana is confined to tropical forests in central South America.