The family Dipodidae includes the birch mice, jumping mice, and jerboas, a total of around 51 species in 15 genera. The skull of dipodids is characterized by an enlarged infraorbital foramen that transmits part of the medial masseter muscle (hystricomorphous) and a separate smaller foramen that transmits the infraorbital nerve and blood vessels. Unlike rodents that exhibit the myomorphous skull condition (the Muridae, for example), dipodids do not have a well-developed zygomatic plate. Even though they are hystricomorphous, dipodids have a sciurognathous lower jaw. The jugal has a branch that extends dorsally to contact the lacrimal. The angular process of the lower jaw is made up of thin bone that is often perforated. The dental formula of dipodids is 1/1, 0/0, 1-0/1-0, 3/3 = 18 or 16. The morphology of the cheekteeth varies considerably, but in all cases they are rooted.
Jumping mice (subfamily Zapodinae) are distributed throughout North America with one species (Eozapus setchuanus) in China. Birchmice (subfamily Sicistinae) occur throughout Eurasia. Jerboas (subfamilies Dipodinae, Paradipodinae, Cardiocraniinae and Euchoreutinae) occur from northern Africa through central Asia.
Jumping mice are well equipped for jumping with long hind feet to propel them off the ground and a long tail that helps them maintain balance while airborne. Jumping mice move either by making a series of long bounds (they can cover up to 10 feet in a single hop), short hops, or by scurrying under vegetation. Jumping mice are nocturnal and hide during the day under logs or in clumps of vegetation.
Birchmice, in contrast to jumping mice, have shorter tails and hindfeet but they still move about primarily by jumping. They are also nocturnal, but unlike jumping mice, they dig shallow burrows and hide in underground nests during the day.
Jerboas are exclusively jumping animals (saltatorial). They have hind limbs that are at least four times as long as their front legs, and the foot bones are often fused into a single long cannon bone, which gives the animal greater leverage for jumping. Jerboas that live in sandy areas have fur on the undersides of their feet, which gives the animal greater traction on the loose sand. The front limbs are not used for locomotion; instead, they are employed in the gathering of food and for burrowing. Jerboas are nocturnal and feed on insects, seeds, and succulent vegetation. In many ways they are remarkably similar to the kangaroo rats (Heteromyidae) of North America. Similarities include greatly inflated bullae; a very long tail, often tipped black and white; strongly saltatorial locomotion with enlarged and powerful hind feet; fused or nearly fused cervical vertebrae; soft, silky pelage, usually pale in color.
Fossil dipodids are known from the Oligocene. Despite the remarkable similarity of some dipodids and heteromyids, these two families are no believed to be especially closely related, and the affinities of the dipodids are not known.
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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