The capybara and the lesser capybara both belong to the subfamily Hydrochoerinae along with the rock cavies. The living capybaras and their extinct relatives were previously classified in their own family Hydrochoeridae.[7] Since 2002, molecular phylogenetic studies have recognized a close relationship between Hydrochoerus and Kerodon, the rock cavies,[8] supporting placement of both genera in a subfamily of Caviidae.[5] Paleontological classifications previously used Hydrochoeridae for all capybaras, while using Hydrochoerinae for the living genus and its closest fossil relatives, such as Neochoerus,[9][10] but more recently have adopted the classification of Hydrochoerinae within Caviidae.[11] The taxonomy of fossil hydrochoerines is also in a state of flux. In recent years, the diversity of fossil hydrochoerines has been substantially reduced.[9][10] This is largely due to the recognition that capybara molar teeth show strong variation in shape over the life of an individual.[9] In one instance, material once referred to four genera and seven species on the basis of differences in molar shape is now thought to represent differently aged individuals of a single species, Cardiatherium paranense.[9] Among fossil species, the name "capybara" can refer to the many species of Hydrochoerinae that are more closely related to the modern Hydrochoerus than to the "cardiomyine" rodents like Cardiomys.[11] The fossil genera Cardiatherium, Phugatherium, Hydrochoeropsis, and Neochoerus are all capybaras under that concept.[11]
The capybara has a heavy, barrel-shaped body and short head, with reddish-brown fur on the upper part of its body that turns yellowish-brown underneath. Its sweat glands can be found in the surface of the hairy portions of its skin, an unusual trait among rodents.[7] The animal lacks down hair, and its guard hair differs little from over hair.[12] Capybara skeleton Adult capybaras grow to 106 to 134 cm (3.48 to 4.40 ft) in length, stand 50 to 62 cm (20 to 24 in) tall at the withers, and typically weigh 35 to 66 kg (77 to 146 lb), with an average in the Venezuelan llanos of 48.9 kg (108 lb).[13][14][15] Females are slightly heavier than males. The top recorded weights are 91 kg (201 lb) for a wild female from Brazil and 73.5 kg (162 lb) for a wild male from Uruguay.[7][16] Also, an 81 kg individual was reported in São Paulo in 2001 or 2002.[17] The dental formula is 1.0.1.3/1.0.1.3. Capybaras have slightly webbed feet and vestigial tails.[7] Their hind legs are slightly longer than their forelegs; they have three toes on their rear feet and four toes on their front feet.[18] Their muzzles are blunt, with nostrils, and the eyes and ears are near the top of their heads. Its karyotype has 2n = 66 and FN = 102, meaning it has 66 chromosomes with a total of 102 arms.[5][7]
Fun Fact: The capybara is the world's largest living rodent.