A really big (but extinct) rodent

Guinea pigs make popular pets nowadays. Eight million years ago, however, it would have been hard to find a cage large enough to hold one.

Back then, a South American rodent called Phoberomys pattersoni grew to be as big as a bison. That’s what researchers conclude from some new Phoberomys fossils in northwestern Venezuela. Analyses of the 8-million-year-old fossils suggest that the rodents could reach a weight of 740 kilograms (or more than 1,600 pounds).

About the size of a bison, this rodent grazed on aquatic grasses and roamed the riverbanks of Venezuela about 8 million years ago.

C.L. Cain/Science

Phoberomys belongs to the caviomorph family of rodents. These are distantly related to modern-day guinea pigs, chinchillas and capybaras (which at 50 kilograms, are today’s largest rodents). Researchers first learned about Phoberomys in 1980. Until recently, their bone and tooth fossils weren’t complete enough for them to estimate the animal’s size.

The new fossil finds suggest that the enormous creatures could sit on their hind legs like modern rodents. They would have used their front paws to handle objects. The researchers also found crocodile, fish and freshwater turtle remains near the Phoberomys fossils. This suggests that the rodents probably spent part of their time in water eating aquatic grasses.

The researchers speculate that Phoberomys was able to get so huge because there weren’t any grazing animals compete with them. What types? Think horses or cows . The rodents disappeared when ferocious predators arrived on the continent.

For us, their extinction is probably a good thing. It might be tough to clean up after your cat if it happened to drag one of these things into the house!