Order Rodentia

Rodentia includes all rodents, such as agoutis, squirrels, jutias, beavers, hamsters, dormice, marmots, prairie dogs, rats, mice, tuco-tuco, and gophers. It is the most diverse order of mammals, containing approximately 50% of all species. This order has, as a unique characteristic, a pair of open-rooted (ever-growing) upper and lower incisors, each elongated, with thick layers of enamel on the front and a softer dentine on the back. The differential wear from gnawing creates perpetually sharp chisel edges; the absence of other incisors and canine teeth results in a diastema on the upper and lower jaws; the articulation of the lower jaw branches ensures that the incisors do not meet when food is chewed and that the upper and lower molariforms do not come into contact while the animal gnaws; the molariform teeth may be either hypsodont or brachydont; the masseter muscle is highly specialized, and its arrangement serves as a basis for differentiating the suborders; feet clawed; fibula not articulating with the calcaneus. There are three suborders in North America: Ctenohystrica, Eusciurida, and Supramyomorpha. They are currently of cosmopolitan distribution.