The Largest Rodent Ever Weighed More Than Three Horses

Written by Emmanuel Kingsley
Published: December 26, 2022
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Contrary to what most people think, rats and mice are not the only kinds of rodents to exist, although they are some of the most common. Apart from being mostly pests, rodents are some of the most successful animals ever to exist. The reason for this is their reproduction rate and also their adaptation skills. These creatures are highly adaptable when it comes to habitats and can be found on every continent except Antarctica. Rodents are currently divided into around 2,277 species that fall under a plethora of orders, suborders, families, and genera.

Although a rodent’s size mostly depends on its species and occasionally on its diet, the fundamental rodent body plan is that of a little, compact, furry, four-limbed mammal with short claws and a long tail. However, there are still some rodents that are bigger than the average description, and even more shockingly, there was once a rodent species that weighed more than three horses. This article addresses this extinct rodent and also gives some random facts.

Meet the Josephoartigasia Monesi

Josephoartigasia monesi

Josephoartigasia monesi lived between the Early Pliocene and Early Pleistocene epochs.

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The Josephoartigasia monesi is an ancient rodent that weighed as much as three horses, and it is almost impossible to imagine what these rodents looked like. These rodents, which lived between the Early Pliocene and Early Pleistocene epochs, have their genus named after José Artigas, a political figure in Uruguay, while the name of the species honors lvaro Mones, who is credited with finding many significant fossils in South America. 

Before fossils of the J. monesi were found, the largest rodent species ever recorded was the Phoberomys pattersoni, an older species that lived in South America and weighed around 1,102 pounds. Based on records, the J. monesi would have weighed twice this size, around 2,670 pounds on average, with a maximum weight of up to 5,701 pounds. Not only were these rodents big, but they were also tall. Their estimated height was around 4.9 feet (1.5 m), and their estimated length was 9.8 feet (3 m). Although these rodents looked much like most rodents do, just so much bigger, it was easy to recognize them by their teeth. They had massive front teeth, which looked much like elephant tusks. Another simple way to identify them was by their enormous heads; the Josephoartigasia monesi’s skull measured up to a length of 53 cm (1.7 ft).

Josephoartigasia Monesi Distribution and Habitat

The preferred habitats of these ancient giant rodents are not fully known, but considering where many fossils have been found, it is evident that they were popular in some parts of South America. The fossils of these rodents were particularly common in the region of the San José Formation in Uruguay. Experts have concluded that since these rodents are thought to be herbivores, the habitat in which they lived at the time was probably an estuary or deltaic system with forest communities.

The first fossil from the genus was found in 1966 during the formation of San José; parts of the teeth were first found and then used to identify the genus. However, the first fossil evidence of the J. Monesi species was discovered in 1987; a skull that had been preserved in a rock in the Barrancas de San Gregorio formation. The skull was about 20 inches long, which was the first indicator of the rodent’s size, proving that the rodent could grow to 2,200 pounds. However, despite this discovery, a full description of the species was not made until 2008.

Diet: What Did the Josephoartigasia Monesi Eat?

Josephoartigasia monesi skull

It is believed that the J. Monesi was completely herbivorous.

©Andres Rinderknecht / CC BY 4.0 – License

Despite having prominent front teeth that could have cut into the flesh of smaller animals, the J. Monesi species is believed to have been completely herbivorous, preferring to eat soft vegetation. Their dominant front teeth also made it possible for them to chew through tough material. However, this rodent had small molars and premolars, which were unsuitable for chewing grass and other abrasive vegetation, making the rodent stick to a diet of aquatic plants and fruits.

These rodents also had really strong incisors that were strong enough to bite through roots. Their front teeth worked almost the same way as elephant tusks, being able to dig up root plants. Because of the size of these rodents, they would have easily been able to digest these root plants without much struggle, like smaller mammals. Additionally, studies indicate that this rodent could have had a bite force of up to 936 pounds. This is up to three times more than a modern tiger’s bite. Experts also believe that their incisors were used as a form of defense against predators that dominated the South American continent at the time. However, because of their size and incredible bite force, it would have been extremely difficult for other animals to prey on these rodents.

Josephoartigasia Monesi vs. Modern Rodents


The capybara, the largest existing rodent, is smaller than Josephoartigasia monesi.

©Henner Damke/

The primary difference between J. Monesi and every other existing rodent species is size, as the J. Monesi is the largest rodent to have ever existed. For reference purposes, the largest existing rodent is the capybara, which weighs around 130 pounds. The majority of rodents have typical petite, short bodies and tiny legs. They also frequently have long whiskers and keen senses that enable them to navigate their surroundings, even in the dark.

Another difference between the J. Monesi species and the rodents that currently exist is their dietary choices. Although some rodents are herbivores, just like the J. Monesi, many can be considered omnivores since they eat other animals alongside plants and fruits. Despite lacking the canine teeth found in most carnivores, several of these rodents are skilled hunters. Numerous species of birds, reptiles, and other mammals are thought to have gone extinct because of rodents like rats. Insects and worms are occasionally consumed by rats, even those that eat plant material. Some also consume tree bark, while others consume fish, eggs, and other small aquatic animals.

Up Next:

The 10 Largest Animals In The World

Are Capybaras the Biggest Rodents in the World?

Are Rodents Mammals?

Discover the Largest Ever Rabbit on Earth – A 50lb Giant

The photo featured at the top of this post is © Andres Rinderknecht / CC BY 4.0 – License / Original

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