Phoberomys

What is Phoberomys?

Phoberomys is an extinct genus of rodent recognized as the largest rodent to have ever lived. Belonging to the infraorder Caviomorpha, it is closely related to the pacarana and shares superficial similarities with the capybara.¹

Living during the Late Miocene and Early Pliocene epochs, these animals inhabited wetlands and swamps in South America. Their anatomy featured massive hind limbs and slender forelimbs, suggesting they may have rested on their haunches while feeding. Their deep jaws and hypsodont teeth were specialized for a gritty, herbivorous diet.¹

Estimating the weight of Phoberomys is complex due to its unusual skeletal asymmetry. While femur-based calculations suggest a mass of approximately 700 kg (1,540 pounds), other estimates based on forelimbs or teeth suggest a range between 170 kg and 440 kg. Regardless of the specific estimate, Phoberomys was significantly larger than any living rodent.¹

When and where did Phoberomys live?

Phoberomys lived during the Late Miocene (approximately 11.6 million to 5.3 million years ago) and the Early Pliocene (5.3 million to 3.6 million years ago) epochs.¹

Geographically, this extinct rodent was restricted to South America, with fossils recovered from sites in Argentina, Brazil, and Venezuela. These animals inhabited environments such as wetlands, nearshore swamps, freshwater rivers, and terrestrial savannas.¹

How big was Phoberomys compared to rodents today?

Phoberomys was significantly larger than any rodent living today. While the capybara—the largest extant rodent—typically weighs between 35 and 66 kg (77 to 146 pounds), Phoberomys estimates far exceed this range.¹²

Scientific estimates for the mass of Phoberomys vary due to the animal’s unusual skeletal asymmetry:

• Femur-based estimate: Approximately 700 kg (1,540 pounds), comparable to an American bison.¹
• Forelimb-based estimate: Approximately 440 kg (970 pounds), similar to a medium-sized moose.¹
• Tooth-based estimate: 170–330 kg (370–730 pounds), similar to a pygmy hippopotamus.¹

Even using the most conservative estimates, Phoberomys was many times heavier than the capybara. It is worth noting that while Phoberomys was massive, the extinct Josephoartigasia monesi is considered the largest rodent ever recorded, with some estimates suggesting it reached nearly 1,000 kg.¹²

What did Phoberomys eat?

Phoberomys was a herbivore that subsisted on a gritty diet, as evidenced by its specialized dental structure. It possessed a deep jaw equipped with hypsodont (high-crowned) teeth, which are characteristic adaptations for processing tough or abrasive plant material.¹

The animal likely fed while resting on its haunches, a posture that would have allowed it to use its smaller forelimbs to gather and manipulate vegetation. Its habitat, which included wetlands, nearshore swamps, and terrestrial savannas, provided a variety of plant resources consistent with this herbivorous lifestyle.¹