What is the Largest Rodent That Ever Lived?

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  • Written By: Michael Anissimov
  • Edited By: Bronwyn Harris
  • Last Modified Date: 24 November 2019
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The largest rodent that ever lived was the size of a cow. It was 3m (9.8 ft) long, with a 1.5 m (5 ft.) tail, and probably weighed around 700 kg (1,543 lbs). This rodent could kill you if it sat on you.

Actually, the figures cited are for Phoberomys pattersoni, which is only the second-largest rodent that ever lived. Its close cousin, Phoberomys insolita, was even a bit larger, but no complete skeleton of it has ever been found, making a precise estimate of its size and weight difficult.

Phoberomys pattersoni lived in the Late Miocene, about 8 million years ago. It dwelled around the Orinoco river delta in modern-day Venezuela, feeding on grasses and shrubs. Its sheer size would have been a deterrent to predators, much like its herbivore contemporaries, the ground sloths.

Like other rodents, Phoberomys pattersoni had large, continuously growing teeth that had to be kept short by gnawing. These teeth, the size of sabers, would have also been used to bite would-be predators. It is not likely that Phoberomys pattersoni had any serious predators, because being so large, it was likely relatively slow, and would have been easy prey for the mega-predators of the time if it couldn't defend itself in a fight. The fact that it even evolved suggests that it could.


Phoberomys pattersoni's natural predators would have included three-meter long crocodiles, saber-tooth cats and huge, flightless carnivorous birds. Living a semi-aquatic lifestyle, it probably ate sea grass.

A full skeleton of the beast was only discovered in 2003. Fragments had been uncovered before, but no one suspected how big the rodent was until the full skeleton was found. Its closest living relative, the South American capybara, can weigh up to 45 kg (99 pounds), 15 times smaller than Phoberomys pattersoni. The capybara is the largest living rodent.

Phoberomys pattersoni managed its huge size by using a different gait than smaller rodents. Its massive stomach would have aided its digestion by functioning as a fermentation barrel to break down stubborn bits of cellulose.


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Post 3

@umbra21 - Hippos are vegetarians but there is plenty of reason to fear those. They are one of the worst killers of humans among all the big animals in Africa.

These giant rodents sound like they are fairly similar, being semi-aquatic and living on sea grass. So they might have been sweet and gentle like manatees are today, or they might have been like hippos. And since hippos are that violent to deal with the predators they face, I would imagine that a cow-sized water-rat would be fairly violent as well, considering it was dealing with massive crocodiles and saber-toothed cats.

Post 2

@irontoenail - Rats and mice have a reputation (and not undeserved) for being dirty as well as being vicious and that might be why some people are afraid of them. They forget that squirrels are rodents as well, and so are guinea pigs, but fewer people are afraid of those.

The difference is that rats are omnivorous. There are plenty of stories about rats taking a bite out of people or animals or even devouring them alive when they have the chance. It sounds like this creature was massive, but not carnivorous so there wouldn't be any reason for a human to fear it.

Post 1

I guess if you have a problem with rodents you probably wouldn't even recognize this creature as being a rodent. My mother is terrified of mice and rats (although she always just says she strongly dislikes them) and will literally jump onto a chair if she thinks one is in the room.

But I suspect that's because they are small and unpredictable rather than because they are actually all that dangerous.

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