ORDER RODENTIA

Largest order of recent mammals. Includes approximately 2/3 of living mammals, 43 families, 443 genera, approximately 2000 species. Distribution: world-wide except for Antarctica.

Defining characteristics:

Most important are: One pair of incisors with enamel only on anterior surface

No canines

Cheek teeth never more than 2/1 premolars, 3/3 molars.

For other characteristics see text Table 18-1, p. 293.

Paleontology: Ancient. Go back to Eocene (56 million yrs ago), with possible precursors in

Paleocene. Over half of the living families were represented as early as the Oligocene. Underwent great adaptive radiation during the Miocene as open grassland areas developed.

Two major divisions appeared early – sciurognathous and hystricognathous types, based on the character of the mandibular apparatus. Taxonomic suborders Sciurognathi and Hystricognathi are based on these characters. See Figure 18-3, p. 295. Students should also know the descriptive terms sciuromorphous, hystricomorphous, myomorphous, and protrogomorphous. See text Fig. 18-2, p. 295, Fig. 18-4, p.296, and definitions in glossary.

For the relationships of the various members of the order, see the cladogram on p.297. No attempt is made here to treat all of the genera and subfamilies. However, some of the larger or peculiar subfamilies are mentioned.

Suborder Sciurognathi

Family Aplodontidae Mountain Beaver. A monotypic family , one genus, one species.

Aplodontia rufa. Not related to our beaver. This is the most primitive of the order.

Prehistorically widespread but now occurs only on west coast from California to British

Columbia. Protrogomorphous masseteric arrangement.

Family Sciuridae Squirrels. A large family represented in both old and new worlds. 50 genera, approx 270 species. 13 species in South Dakota. Students should know the genera represented in the state. Note the genus Glaucomys (flying squirrel) and compare with scaly-tailed flying squirrel Fig.18-24, p. 313, as an example of parallelism.

Family Castoridae Beaver. One genus, 2 species. Castor canadensis in N. America, and Castor fiber in Europe and Asia.

Family Geomyidae Pocket Gophers. 5 genera, 35 species. Two genera in S. Dakota, Thomomys and Geomys.

Family Heteromyidae Pocket mice. 6 genera, 59 species. 5 species of the genera Dipodomys and Perognathus in S. Dakota

Family Dipodidae Jerboas, jumping mice and birch mice. 15 genera, 51 species. Many American authors place the jumping mice and birch mice in a separate family Zapodidae. Genus Zapus with two species in S. Dakota.

Family Muridae Rats and mice. As treated by most European authors, includes 2/3 of the recent mammals. 281 genera, approximately 1300 species. Most American authors consider the New World rats and mice to be in the family Cricetidae, with subfamilies Cricetinae and Arvicolinae. In this classification, Peromyscus, Reithrodontomys, and Neotoma are included in the Cricetinae, and the voles and lemmings are placed in the Arvicolinae. The Muridae are a very diverse family, having a long history of specializing to take advantage of different habitats. Note the subfamily Spalacinae, blind mole rats, that have habits much like our pocket gophers – another example of parallelism within this large family.

Family Anomaluridae. Scaly-tiled squirrels. 3 genera with 7 species. Western and central Africa. (Fig.18-24, p. 313)

Family Pedetidae Springhaas or Springhare. Monotypic, one genus and species. East and South Africa. Approximately the size of a rabbit. Of interest because it parallels the kangaroos in its form and habits

ORDER RODENTIA Suborder Hystrichognathi

Defining characters: See table 18-3, p. 315. Most important: Mandible hystrognathous; infraorbital foramen much enlarged and hystricomorphous.

Paleontology: Late Eocene to early Oligocene.

Distribution: Old World members of this suborder are found across a broad area of the Old World: southeastern Europe, Middle East, Southeast Asia, and much of Africa. New World forms are primarily South American. There is considerable controversy over this distribution. Some authors believe that the New World forms evolved independently, but the prevailing opinion is that the suborder has an African origin.

New World Hystricognathi

Family Erethizontidae New World porcupines. 4 genera, 12 species occurring primarily in the northern half of South America, but the species Erethizon dorsatum occurs as far north as arctic North America.

Family Chinchillidae 3 genera, six species. Found in the Andean regions of the southern half of South America. Moderate size, 2 – 20 pounds. Adapted to high altitude cold. Fur is extremely fine and dense. Originally jealously protected from export to maintain a monopoly on its valuable fur. Now, however, may be found in pet shops.

Family Dinomyidae A monotypic family. The single genus and species, Dinomys branickii is very rare and may be near extinction. The family is of interest because an extinct member of the family was as large as a rhinoceros.

Family Caviidae 5 genera with 14 species. Includes the guinea pig and similar species, as well as more cursorial types such as members of the genus Dolichotis that have long slender legs. Some species may weigh up to 35 pounds.

Family Hydrochaeridae A monotypic family. The single species, the capybara, is the largest living rodent. It occurs from Panama south through the northern part of South America east of the Andes. It leads a semiaquatic life, resembling that of the hippopotamus.

Families Dasyproctidae and Agoutidae Members of both families are commonly called agouties, although the agoutids are also call pacas. See Fig. 18-34, p. 321 and account on this page and next.

Family Ctenomyidae Tuco-tucos. 1 genus with 13 species. These are relative small, fossorial rodents that are similar to our pocket gophers in form and habits. Another case of parallism among the rodents.

Family Octodontidae Degus or rock rats. Fig. 18-35.

Family Echimyidae Spiny rats. A large family of 20 genera with 78 species. Occurs throughout the approximate northern half of South America.

Family Capromyidae Hutias. West Indies. 8 genera, 20 species. Some of the species are extinct now, and others are considered endangered.

Family Myocastoridae Nutria. A monotypic family. Myocastor coypus is a large rodent superficially resembling our beaver in form and habits. From southern South America, it has been introduced into our southern states and into Europe. It sometimes does much damage to the environment and may be considered a pest.

Old World Hystricognathi

Family Bathyergidae Mole rats. 5 genera, 9 species. Found in Eastern and South Africa. Fossorial, similar in many respects to our pocket gophers. Ears small or without pinnae, large protrusive incisors that are used to dig with, in contrast to our gophers digging only with their claws. Two of the genera (Heterocephalus, Cryptomys) live as eusocial colonies with one non-working queen, two classes of workers, and one male class.

Family Hystricidae Old World porcupines. 3 genera, 11 species. Occur throughout Africa, southern Europe and east across to the Philippines. Very similar in form and habits to our porcupine, except that the quills are very large, up to 10 inches long.

Two other families, Heteromyidae and Thryonomyidae include only three species.