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A giant rat that lived 10million years ago has been found by scientists.

The swamp monster measured 5ft – the same size as singer Dolly Parton.

The 13-stone Neoepi-blema acreensis was one of the biggest rodents to ever roam South America.

But two skulls found in the Brazilian Amazon also showed that the rodent had a tiny four-ounce brain.

The creature, related to chinchillas, had few predators which meant it didn’t need to think too much.

The study’s lead author Dr Jose Ferreira said: “Neoepiblema was about five feet long and weighed around 80 kg (12.6st), which surpassed the capybara, the largest living rodent which is about 60 kg (9.5st).

(Image: Getty Images)

“This rodent is an extinct relative of the chinchillas and pacaranas and inhabited the western Brazilian Amazonia about 10 million years ago.

“It lived in swampy environments that existed there before the emergence of one of the largest tropical forests in the world.”

Dr Ferreira, of the Federal University of Santa Maria, said it lived when South America was a “giant island” cut off from North America and Antartica.

(Image: Márcio L. Castro /SWNS.COM)

He said: “Although Neoepiblema was one of the largest rodents ever, the brain of this giant rodent was very small relative to its body mass.

“The main predators of these giant rodents were crocodilians, who were also giants and inhabited the marshy regions. They were not active predators, as are mammals.

(Image: Márcio L. Castro /SWNS.COM)

“There was no need for giant rodents to have large brains since this would imply unnecessary energy consumption.

“The same pattern has been documented in animals that live on islands where there are no large predatory mammals.”

The research has been published in the journal Biology Letters.

(Image: Márcio L. Castro /SWNS.COM)

The largest fossil rodent ever found is the buffalo-sized Josephoartigasia monesi.

It weighed an estimated body mass of 2,200lbs (1,000kg), was closely related to guinea pigs and lived in South America three million years ago.

The largest living rodent is the capybara which can grow to four feet in length and weigh around seven stone.