Josephoartigasia monesi was the largest rodent ever discovered, akin to a giant capybara, weighing up to 1,000 kg. It lived in South America around 3 million years ago, likely inhabiting riverbanks and wetlands. Its massive incisors suggest a diet of tough vegetation and a social, herbivorous lifestyle.

Josephoartigasia monesi is known to have inhabited South America, specifically in what is now Uruguay. Fossils of this species were discovered in the San José Formation, which dates back to the Pliocene and Pleistocene epochs, approximately 4 to 2 million years ago.

During the time of Josephoartigasia monesi, the region likely featured a mix of subtropical to temperate climates. The landscape would have been diverse, with a range of environments including grasslands, wetlands, and forested areas. These conditions would have provided ample vegetation for grazing and browsing, which is consistent with the herbivorous diet inferred for this species.

Josephoartigasia monesi occupied the ecological niche of a large herbivore. As one of the largest rodents ever discovered, it likely played a significant role in its ecosystem, shaping vegetation dynamics and possibly influencing the habitats of other contemporary species. Its size and likely social behavior may have also provided defense mechanisms against predators.