The suborder SCIUROMORPHA is distributed worldwide apart from Australia and Antarctica. Sciuromorphs are distinguished by the arrangement of the masseter muscle, whose deep branch in these rodents is used to close the jaws while the lateral branch (attached to the snout in front of the eyes) controls the action of the incisors. This is the reverse of the case with caviomorphs. Contrary to what might be expected from their name, not all sciuromorphs are arboreal.
| Common Name | Species Name | Origin | Comments |
| Mountain Beaver | Family Aplodontidae | Western seaboard of N. America | Consists of one single species, the mountain beaver or sewellel, Aplodontia rufa.. |
| Squirrels | Family Sciuridae | Worldwide except for Australia, Saharan Africa and southern South America. | Largest family among the scuiromorphs and one of the most diverse. It contains not only the tree squirrels but also ground squirrels such as chipmunks, marmots and prairie dogs, all of which burrow, and flying squirrels. |
| Scaly-Tailed Squirrels | Family Anomaluridae | Western central Africa | The common name of these squirrels is derived from the scales around the base third of their tails, the function being to provide extra support when climbing in the trees. There are seven species in total about whom not much is yet known. |
| Springhare | Family Pedetidae | Southern Africa | Consists of single species, the springhare Pedetes capensis. |
| Beavers | Family Castoridae | N. America and Eurasia | A family of just two species whose impact on the environment is nevertheless profound due to their damming activities. The beavers are in physical size the second largest rodent after the S. American capybara and are unique in mammals in possessing a cloaca, a structure normally found only among amphibians, reptiles and birds. Apart from its usual function of excretion and reproduction the cloaca also contains the castor glands and anal glands which are used for scent-marking. |
| Pocket Gophers | Family Geomyidae | N. America south to C. America | Pocket gophers are burrowing rodents with fur-lined cheek pouches. They tend to be territorial and anti-social except during the breeding season. 34 species are recognised, but there is apparently a multitude of subspecies. |
| Pocket Mice | Family Heteromyidae | W. & S. USA through to northern S. America | Similar to the Geomyidae in possessing cheek pouches, although pocket mice can turn theirs inside out. There are five genera, including the kangaroo mice, kangaroo rats and spiny pocket mice. |
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