The New World porcupines, or Erethizontidae, are large arboreal rodents, distinguished by the spiny covering from which they take their name. They inhabit forests and wooded regions across North America, and into northern South America. Although both the New World and Old World porcupine families belong to the Hystricognathi branch of the vast order Rodentia, they are quite different and are not closely related.
New World porcupines are stout animals, with blunt rounded heads, fleshy mobile snouts, and coats of thick cylindrical or flattened spines ("quills"). The spines are mixed with long soft hairs. They vary in size from the relatively small Prehensile-tailed Porcupines, which are around long, and weigh about , to the much larger North American Porcupine, which has a body length of , and weighs up to .
They are distinguished from the Old World porcupines in that they have rooted molars, complete collar-bones, entire upper lips, tuberculated soles, no trace of a first front-toe, and four teats.
They are less strictly nocturnal than Old World species in their habits, and some types live entirely in trees while others have dens on the ground. Their long and powerful prehensile tails help them balance when they are in the tree tops. Their diet consists mainly of bark, leaves and conifer needles but can also include roots, stems, berries, fruits, seeds, nuts, grasses and flowers. Some species also eat insects and small reptiles. Their teeth are similar to those of Old World porcupines, with the dental formula:
Solitary offspring (or, rarely, twins) are born after a gestation period of up to 210 days, depending on the species. The young are born fully developed, with open eyes, and are able to climb trees within a few days of birth.
The tree porcupines (Coendou, Sphiggurus, and Echinoprocta) contain 15 species. They are found throughout tropical South America, with two extending into Mexico. They are of a lighter build than the ground porcupines, with short, close, many-coloured spines, often mixed with hairs, and prehensile tails. The hind-feet have only four toes, owing to the suppression of the first, in place of which they have a fleshy pad on the inner side of the foot; between this pad and the toes, branches and other objects can be firmly grasped as with a hand. These three genera are often united into a single genus Coendou.
Genus Chaetomys, distinguished by the shape of its skull and the greater complexity of its teeth, contains C. subspinosus, a native of the hottest parts of Brazil. This animal is often considered a member of the Echimyidae on the basis of its premolar.