There are about fifty-nine members of the family Heteromyidae divided among six genera. They are all small rodents, the largest being the giant kangaroo rat (Dipodomys ingens) with a body length of 15 cm (6 in) and a tail a little longer than this. In many species the tail is tufted and is mainly used for balance. Other adaptations include partially fused vertebrae in the neck, short fore limbs and much enlarged bullae (bubble-shaped bones in the skull). The skulls vary widely across the group but they are all thin and papery and do not have the robust cranial crests and ridges found on the skulls of members of the family Geomyidae. The skull has other peculiarities. There is an extra hole that penetrates the rostrum, distinctive occluded teeth and the masseter muscle, which moves the lower jaw, is set far forward on the snout, an arrangement found in squirrels, beavers, pocket gophers, heteromyids and a few other groups. The dental formula is 1. 0. 1. 31. 0. 1. 3 × 2 = 20 teeth in total. In the kangaroo rats, the teeth continue to grow all the time, being worn away as the animal chews. The molars have two-lobed cusps. The upper incisors are grooved and the enamel on the molars is quickly worn away by chewing leaving the dentine exposed. In the kangaroo rats they are unrooted but in the pocket mice they have roots.
A kangaroo mouse is either one of the two species of jumping mouse ( genus Microdipodops ) native to the deserts of the southwestern United States , predominantly found in the state of Nevada . The name " kangaroo mouse" refers to the species' extraordinary jumping ability, as well as its habit of bipedal locomotion. The two species are:
Kangaroo mouse , (genus Microdipodops ), either of two species of leaping bipedal rodents found only in certain deserts of the western United States. They have large ears and a large head with fur-lined external cheek pouches. The forelimbs are short, but the hind limbs and feet are long. Stiff hairs fringe the hind feet, and the soles are densely furred. The soft, silky coat is long and lax.