Rats & super-rats...

Via the Times:

The fossilised skull of a rat the size of a car has been unearthed. The creature lived about four million years ago, weighed about a tonne and ate mostly soft vegetation. It was so big that it probably spent much of its life semi-submerged in water, like a hippo, to reduce the stresses caused by its size.
Palaeontologists found the skull in rock deposits in Uruguay. It is believed to date back two to four million years to a time when giant wildlife was commonplace in South America.
The rodent, Josephoartigasia monesi, was uncovered by Andrés Rinderknecht and Ernesto Blanco. It has been nicknamed Mighty Mouse and is thought to have been similar to the capybara and pacarana, much smaller creatures that are still found in South America. Capybaras are the biggest living rodents at just over 60kg fully grown, while pacaranas weigh 15kg. The common rat weighs about 300g.
J. monesi is thought to have weighed about a tonne and the biggest specimens could have been more than 2.5 tonnes — about the same as hippopotamuses, which range from 1.4 tonnes to 3.2 tonnes.