The order Rodentia represents the largest group of mammals on the planet, encompassing over 2,000 living species. This taxonomic group includes familiar animals like the common mouse and the squirrel, but also massive species that challenge the typical perception of a small, scurrying creature. The size variation within this order is immense, ranging from tiny species weighing only a few grams to animals that can exceed the size of a large dog.
The Undisputed King: The Capybara
The largest living rodent in the world is the Capybara, scientifically known as Hydrochoerus hydrochaeris. This massive herbivore, a native of South America, exhibits a barrel-shaped body that can reach a length of up to 1.3 meters (4.4 feet) and stand roughly 60 centimeters (two feet) tall at the shoulder. Adult Capybaras typically weigh between 35 and 66 kilograms (77 to 146 pounds), though exceptionally large females have been recorded exceeding 90 kilograms.
Their natural habitat spans a vast area east of the Andes mountains, covering nearly every country in South America except Chile. Capybaras are semi-aquatic mammals, intrinsically linked to bodies of water such as rivers, lakes, swamps, and marshes. They possess partially webbed feet that aid in swimming and have unique facial features, including eyes, ears, and nostrils located high on the head. This allows them to keep their sensory organs above the surface while the rest of their body remains submerged for cooling or predator evasion.
Capybaras are social animals, relying on group living for safety and resource management. They typically live in family groups of 10 to 20 individuals, though these groups can coalesce into much larger herds near shrinking water sources during the dry season. Communication within the group involves a variety of vocalizations, including purrs and barks, which help maintain social bonds and signal potential danger. They spend their days grazing on grasses and aquatic plants and are often seen resting in the water to manage their body temperature in the tropical climate.
The Next Tier of Large Rodents
While the Capybara is the largest, several other species rank highly, with the North American Beaver (Castor canadensis) often considered the second largest globally. These aquatic engineers are widely distributed across North America and are known for their ecological role in building dams and lodges. A mature North American Beaver commonly weighs between 16 and 31.5 kilograms (35 to 70 pounds), though specimens exceeding 45 kilograms (100 pounds) have been recorded.
The Eurasian Beaver (Castor fiber), a closely related species, is generally smaller, with adults peaking at weights around 30 kilograms (66 pounds). The Cape Porcupine (Hystrix africaeaustralis), found in southern Africa, is the largest porcupine species. This terrestrial rodent can also reach weights of up to 30 kilograms, distinguished by its long, formidable quills used for defense.
Other Large Rodents
The Nutria, or Coypu (Myocastor coypus), also contributes to this group of large rodents. Native to South America, this semi-aquatic rodent has been introduced globally and typically weighs between 7 and 10 kilograms (15 to 22 pounds).
Defining the Rodent Order and Size Extremes
The unifying and defining feature of the Order Rodentia is a specialized dental structure adapted for gnawing. All rodents possess a single pair of continuously growing, rootless incisor teeth in both the upper and lower jaws. These teeth have a hard layer of enamel on the front surface and softer dentine on the back. The differential wear created during gnawing causes the softer material to wear away faster, constantly sharpening the enamel edge into a chisel-like blade.
This dental mechanism necessitates a rodent’s constant need to chew and wear down its teeth. This feature connects the smallest members of the order, such as the Pygmy Jerboa, which weighs only a few grams, to the Capybara. The size range becomes even more dramatic when considering extinct species. The largest rodent known to have ever lived was Josephoartigasia monesi, an extinct species that roamed South America during the Pliocene and Pleistocene epochs. Estimates based on skull size suggest this prehistoric giant may have weighed as much as 1,000 kilograms (over 2,200 pounds).