Big Rats
The capybara,as the one shown here, are the world's largest living rodents -- capable of weighing up to 132 pounds. Palaeontologists are engaged in a fierce debate over the remains of a rat-like beast dubbed Josephoartigasia monesi. Uruguayan palaeontologists said the rodent would have weighed just over a ton but an expert at McGill University estimates it would have weighed just 770 pounds.