In the New World the porcupines are represented by the members of the family Erethizontidae, or Coendidae, which have rooted molars, complete collar-bones.
The policy of the government which protects game, both in the park and in the surrounding national forests, has induced elk, deer, antelope, mountain-sheep, bears, porcupines, coyotes, squirrels, gophers and woodchucks to take shelter here.
In most species there are three circumvallate papillae at the base, and the apical portion is generally covered with small, thread-like papillae, some of which in the porcupines become greatly enlarged, forming toothed spines.
The scapula is usually narrow, with a long acromion; the clavicles may be altogether absent or imperfect, as in porcupines, cavies and hares, but in most species are well developed.
In the squirrels and porcupines the tibia and fibula are distinct, but in rats and hares they are united, often high up. The hind foot is more variable than the front one, the digits varying in number from five, as in squirrels and rats, to four, as in hares, or even three, as in the capybara, viscacha and agouti.