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family myocastoridae

(nutria, coypu)

The single Recent species in this family was originally restricted to central and southern South America, but it has been introduced widely in the United States and Europe.

Nutria are large rodents, weighing up to 10 kg. They have a robust body that shows many indications of their aquatic lifestyle. The ears and eyes are small. The webbed hind feet are large and have 5 toes. Four toes are found on the forefeet, which lack webbing. All toes have well-developed claws. The tail is long, scantily furred, and rounded. It is not compressed as in beavers or muskrats.

Like many aquatic mammals, nutria have thick, soft underfur overlain with long and coarse guard hairs. Their color is dark dorsally and whitish yellow on the underside.

The cranium of a nutria is massively built, with well-developed ridges (including a sagittal crest) and a deep rostrum. Nutrias are hystricomorphous, and their infraorbital foramina lack a distinct groove for the passage of nerves to the rostrum. The zygomatic arches are heavy and broad, but the jugal does not contact the lacrimal. On the ventral surface of the skull, the auditory bullae are small but the paroccipital processes are unusually long. The lower jaws are strongly hystricognathous. The coronoid process is reduced to little more than a knob.

Nutrias have the following dental formula: 1/1, 0/0, 1/1, 3/3 = 20. The molars are hypsodont, flat-crowned, and rooted. The upper molars have two labial and two lingual folds, while the lowers have one labial and three lingual. The incisors are massive and chisel-like, deeply orange-yellow in color.

Nutria are primarily herbivorous, feeding on vegetation on land and in shallow water, but they also consume some invertebrates. They are excellent swimmers, capable of staying underwater for up to around 5 minutes. They prefer slow-moving streams, lakes, and brackish or freshwater marshes. They are good diggers, constructing burrows in river banks. Nutria often live in groups of up to 10-15 individuals, usually made up of parents and offspring.

The fur of these animals has been the basis of a considerable industry, first in their native South America, and more recently in the United States. Nutria have been introduced many times to North America and Europe, both intentionally and accidentally as a result of escapes from fur farms. They can be tremendously destructive to both wild vegetation and to agriculture.

Families of Order Rodentia

Suborder Sciurognathi

Family Aplodontidae (mountain beaver, sewellel)
Family Sciuridae (squirrels)
Family Castoridae (beavers)
Family Geomyidae (pocket gophers)
Family Heteromyidae (kangaroo rats, pocket mice, and allies)
Family Dipodidae (birch mice, jumping mice, jerboas)
Family Muridae (familiar rates and other rodents)
Family Anomaluridae (scaly-tailed squirrels)
Family Pedetidae (spring hare, springhaas)
Family Ctenodactylidae (gundis)
Family Myoxidae (dormice and hazel mice)

Suborder Hystricognathi

Family Bathyergidae (mole rats, blesmols, and rats)
Family Hystricidae (Old World porcupines)
Family Petromuridae (rock rat or dassie rat)
Family Thryonomyidae (cane rats or grasscutters)
Family Erethizontidae (New World porcupines)
Family Chinchillidae (Chinchillas and viscachas)
Family Dinomyidae (pacarana, branick rats, false paca)
Family Caviidae (cavies and  guinea pigs)
Family Hydrochaeridae (capybara)
Family Dasyproctidae (agoutis, acouchis)
Family Agoutidae (pacas)
Family Ctenomyidae (tuco-tucos)
Family Octodontidae (degus, coruros, rock rats)
Family Abrocomidae (chinchilla rats, chinchillones)
Family Echimyidae (spiny rats)
Family Capromyidae (hutias, zagouties, cavies, Indian coneys)
Family Heptaxodontidae (Quemi, giant hutias)
Family Myocastoridae (nutria, coypu)

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