This family contains 9 species placed in 6 genera. They are found in Peru, Bolivia, Chile, and Argentina, occupying habitats ranging from coastal scrub at sea level to barren rocky outcrops at around 3500 m elevation.
Octodontids are small, rat-like rodents, with head and body up to around 200 mm in length, and 300 gms weight. Their tails are long, frequently tufted in scansorial species and short in fossorial ones. They are easily lost in encounters with predators. Members of this family have large heads, pointed noses, and moderately large and rounded ears. Long vibrissae arise from the face. The legs are short; the forefeet have 4 digits and the hindfeet 5; and the toes end in sharp, curved claws. The bodies of octodontids are usually covered with long, dense, and silky fur with well-developed underfur. Dense short hairs cover the tail; these increase in length toward the tip. A "comb" of stiff hairs extends slightly beyond the middle digits of the hind feet. Most species are grayish above and paler below, but one, Spalacopus, is almost entirely black.
The skulls of octodontids are relatively stout and angular in appearance. They are hystricomorphous and strongly hystricognathus, with the angular process markedly deflected. The dentary has a well-developed coronoid process. The zygomatic arch is simple and the jugal does not contact the lacrimal. A small canal separate from the infraorbital carries nerves to the face. The bullae are large except in the most fossorial forms, and the paroccipital processes are short and fused to the bullae. The dental formula of octodontids is 1/1, 0/0, 1/1, 3/3 = 20. Incisors are fairly strongly developed, and the cheekteeth are flat crowned, hypsodont, and distinctively "8"-shaped due to single labial and lingual folds (these folds are very shallow in Octodontomys).
All species are good diggers and live in burrows, but some genera (Aconaemys and especially Spalacopus) are extremely fossorial, with the small limbs and fusiform bodies typical of rodents that spend most of their lives underground. Most live in colonies; some show complex social behavior. All are primarily herbivorous. Degus (Octodon) are agricultural pests in some areas. Degus are unusual in that most of their activity is apparently diurnal.
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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