Key to the Major El Paso Regional Groups of Rodents


1. Infraorbital foramen very large, larger than foramen magnum: 2

1'. Infraorbital foramen smaller than foramen magnum: 3

2. Dorsal hairs in part modified to form stout spines: Erethizontidae, Erethizon dorsatum.

2'. Dorsal hairs not so modified: Myocastoridae (Echimyidae), Myocastor coypus.

3. Tail dorsoventrally flattened, broad and naked: Castor canadensis.

3'. Tail not dorsoventrally flattened: 4

4. Infraorbital foramen a vertically elongate V-shaped slit; cheek teeth 3/3: 5

4'. Infraorbital foramen not as above; cheek teeth more than 3/3: 6

5. Cusps of molars in three longitudinal rows; tail mostly naked: Muridae

5'. Cusps of molars in two longitudinal rows; tail haired: Cricetidae

6. Infraorbital foramen a very small canal or round hole; tail, if elongate, not naked and scaly: 7

6'. Infraorbital foramen an ovoid hole; hind feet elongate; tail elongate, naked, and scaly: Family Dipodidae, Zapus.

7. External fur-lined cheek pouches present; prominent postorbital processes lacking: 8

7'. External fur-lined cheek pouches absent; prominent postorbital processes present: Family Sciuridae.

8. Skull heavy, zygomatic breadth greater than mastoid breadth; tail less than three-quarters head and body length; claws on forefeet at least somewhat enlarged for digging: Family Geomyidae.

8'. Skull light; zygomatic breadth less than mastoid breadth; tail more than three-quarters head and body length; claws on forefeet not greatly modified for digging: Family Heteromyidae.

Key modified from Findley (1987).


Last Update: 2 Nov 2007