Hystricomorpha

Century Dictionary and Cyclopedia

1. A series of simplicident rodents; one of three prime divisions of rodents, including the porcupines and their congeners. The group is characterized by normal upper incisors and distinct tibia and fibula, the angular part of the mandible springing from the outer side of the bony covering of the incisor. The dental formula is : 1 incisor in each half-jaw above and below, no canines, and 1 premolar and 3 molars in each upper and lower half-jaw in all, 20(except in Ctenodactylus, which has no premolars). The skull has no distinct postorbital process (except in Chætomys). The group corresponds to the Hystricina of Waterhouse, and includes the seven families Hydrochœridæ, Caviidæ, Dinomyidæ, Dasyproctidæ, Chinchillidæ, Hystricidæ, and Octodontidæ. There is the greatest diversity in the external aspect and habits of these animals, few of which specially resemble porcupines in general appearance. Except four remarkable outlying genera of Octodontidæ and the old-world porcupines of the genera Hystrix and Atherura, the whole series is American, and almost confined to South America; for there are only three West Indian forms (as Capromys), and only two species of porcupine, of the genus Erethizon, occur in North America.

WordNet 3.0

1. n. an order of rodents including: porcupines; guinea pigs; chinchillas; etc.