The subfamily Hydrochoerinae includes two genera and four species: two species of capybaras (Hydrochoerus) and two species of rock cavies (Kerodon). Kerodon species are medium-sized rodents, approximately 800 grams. Capybaras are the largest rodents in the world. An adult may weigh as much as 60 kg and stand 60 cm high at the shoulder. Extinct species in this subfamily were larger than modern capybaras, reaching or exceeding the size of a large bear. This subfamily is found only in the tropics of South America north to Panama.
Capybaras have heavy, barrel-shaped bodies. Their scientific name means "water hog" and indeed their bodies are hog-like, but they are rodents, not artiodactyls. And unlike hogs, they have short and deep heads. Their external ears and eyes are small; these and the nostrils sit high up on the rostrum, so that they lie above water level when the animal is mostly submerged. A capybara's legs are not long, and the front legs are shorter than the hind. Their tails are extremely short, appearing to be missing altogether. The forefeet have 4 digits and the hindfeet 3, and each toe is tipped with an almost hoof-like claw. Webbing partially connects the digits. The fur is coarse and sparse, consisting mostly of bristle-like hairs; the brown or gray skin can be seen through the hairs (which themselves are brown).
The skull of a capybara is very much like that of a guinea pig ( Caviidae), except that it is very much larger and more robust. Capybaras are classified with the hystricognaths, but their jaws appear to have secondarily become almost sciurognathous. They are, however, hystricomorphous, with large infraorbital canals through which runs the medial masseteric musculature. Like the caviids, capybaras have a pronounced masseteric crest on the sides of the mandibles; this crest is separated from the toothrow by a deep groove. Capybaras also have unusually large paroccipital processes. Their auditory bullae are not enlarged. The toothrows converge anteriorly, so that the palate is shaped like an inverted "V." The zygomatic arches are robust, but the jugal does not contact the lacrimal.
The cheek teeth of capybaras are like those of no other mammals, distinctively flat crowned and hypsodont. The third upper molar is the most unusual, being extremely long and made up of a series of 9 or 10 transverse plates ( loxodont). The dental formula is 1/1, 0/0, 1/1/, 3/3 = 20. The incisors are massive and chisel-like.
Capybaras are semiaquatic, living near ponds, rivers, or swamps and feeding on aquatic plants. They associate in groups of 10 or more individuals, and at times several groups may forage together, forming a much larger herd. These groups have a fairly permanent membership, consisting of of a dominant male, one or more adult females and their infants, and sometimes subordinant males. Capybaras are excellent swimmers, capable of diving and remaining beneath the surface for as long as 5 minutes. They also have the habit of submerging so that only their nostrils are above the surface. If threatened, their usual response is to flee into the water. Jaguars may have been their most important predators, but some are probably killed by anacondas and caimans. Kerodon species are also highly social and males form harems. They are found in rocky, arid habitats.
A male capybara has a distinctive scent gland called a "morrillo" that appears as a dark, oval-shaped, hairless bump on top of its rostrum. Both sexes have large anal glands. They also use a number of vocal signals to communicate.
Capybaras are raised commercially in some parts of South America, providing both meat and leather to the farmer.
References and literature cited:
Feldhamer, G. A., L. C. Drickamer, S. H. Vessey, and J. F. Merritt. 1999. Mammalogy. Adaptation, Diversity, and Ecology. WCB McGraw-Hill, Boston. xii+563pp.
Macdonald, David. 1984. The encyclopedia of mammals. Facts on File Publications, New York.
Nowak, R. M. and J. L. Paradiso. 1983. Walker's mammals of the world. The Johns Hopkins University Press, Baltimore and London, pp 803-810.
Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, Fort Worth. vii+576 pp.
Vaughan, T. A., J. M. Ryan, N. J. Czaplewski. 2000. Mammalogy. Fourth Edition. Saunders College Publishing, Philadelphia. vii+565pp.
Wilson, D. E. and D. M. Reeder (eds.). 1993. Mammal species of the world: A taxonomic and geographic reference, 2nd ed.. Smithsonian Institution Press, Washington and London.
Woods, C. A. 1984. Hystricognath rodents. Pp. 389-446 in Anderson, S. and J. K. Jones, Jr. (eds.). Orders and familes of mammals of the world. John Wiley and Sons, New York.
Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
having the capacity to move from one place to another.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate