A capybara's front teeth never stop growing, which places it squarely among the rodents, yet its body plan reads more like a small ungulate. Adults commonly weigh between 35 and 66 kg and stand about half a metre at the shoulder. Partly webbed feet, a nearly absent tail and a high-set face all serve the same purpose: moving and hiding in water.
The animal is a hindgut fermenter with a large caecum, and it practises coprophagy, re-ingesting soft morning faeces to extract nutrients that a single pass through the gut leaves behind. Grass is abrasive and low in protein, so the strategy matters. Groups typically number about ten to twenty animals, and merge into larger aggregations in the dry season, when receding water concentrates them.
What is often garbled is the size record. The capybara is the largest extant rodent, not the largest rodent that ever lived. Fossil caviomorphs such as Josephoartigasia monesi were far heavier, though published body-mass estimates for that animal vary widely and remain contested.