Buffalo-sized guinea pig revealed

(New Scientist) The full magnitude of the world’s largest ever rodent has been revealed- the now-extinct monster was the size of a cow.

The creature weighed in at 700 kilograms and lived eight million years ago, roaming the lush banks of the ancient Orinoco delta in northwestern Venezuela. But the three-metre-long, 1.3-metre-tall behemoth was an evolutionary cousin of today’s humble guinea pig.

Phoberomys pattersoni would have lived a semi-aquatic life, munching sea grass and dodging other strange, gargantuan creatures such as three-metre-long crocodiles, lion-sized marsupial cats and huge, flightless carnivorous birds, according to Marcelo S?nchez-Villagra, of the University of T?bingen, Germany, who led the new study.

	The 700-kg guinea pig would once have eaten sea grasses on the lush Orinoco delta (Image: Science/Carin L Cain)

S?nchez-Villagra and his team were able to build up a picture of the giant rodent, after finding an “exceptionally complete” skeleton in the Urumaco formation in Venezuela.

“Imagine a weird guinea pig, but huge, with a long tail for balancing on its hind legs and continuously growing teeth,” he says. It was 10 times heavier than its closest living relative – the South American capybara.

“This is a really stunning animal,” says Neill Alexander, a zoologist at the University of Leeds, UK. “However the question is not how is this animal is possible, but why aren’t there others like it?”

Teeth and bone fragments

Orangel Aguilera, one of the team, discovered the skeleton after one of his students stumbled across a bone sticking out of some sediment. It was nicknamed Goya after the area in which it was found.

Phoberomys had previously been identified from only isolated teeth and bone fragments, so no one had realised how immense it was. But analysis of Goya’s skeleton enabled the team to estimate its body mass and gave clues to how it lived.

Alexander says two major impediments to being so big may not have been problematic after all. Bearing its own weight – 1400 times heavier than a pet guinea pig – could have been managed by using a different gait to small rodents.

“Mice and other small rodents stand as if they are doing press-ups,” he says. But larger mammals keep their legs straight. Capybaras stand like sheep, and Goya would have stood even straighter, Alexander says. “If you saw this animal in the distance on a misty day it would look much more like a cow or buffalo, than like a guinea pig.”

Monster meal

Goya’s huge size could also have posed a problem because of the vast amount of food it would need. But its size may have actually helped it efficiently ferment large amounts of plant cellulose in its vat-like gut.

Alexander speculates that the reason giant rodents no longer exist is because they would be slower and less able to escape predators than hoofed animals, such as antelopes, which are more lithe-limbed. However, smaller rodents with short paws can swiftly burrow away to safety.

“Just suppose Goya was around today,” he told New Scientist. “I suggest it wouldn’t last very long, for example, if you put it down in the Serengeti.”