An almost complete skeleton was discovered in Urumaco, Venezuela in 2000. The new species was later classified with the name Phoberomys pattersoni in honor of palaeontologist Brian Patterson. From the fossil, researchers have been able to reconstruct its size and probable lifestyle. It was 3 m (9.8 ft) long, with an additional 1.5 m (4.9 ft) tail, and probably weighed around 700 kg (1,500 lb) (another source gives a more modest estimate of around 250 kg (550 lb)), making it for some years the largest known rodent for which a good size and weight estimate was possible. Its congener Phoberomys insolita was a bit larger still, but it is not known from any reasonably complete remains and thus its size cannot be estimated more precisely.
In early 2008, the discovery of Josephoartigasia monesi was announced, which was even larger.