Key to Regional Squirrels


1. Tail less than one-third total length, condylobasal length more than 60 mm: 2

1'. Tail more than one-half total length; condylobasal length less than 60 mm: 4

2. Maxillary tooth-rows approximately parallel; condylobasal length more than 80 mm; front feet with four clawed digits: Marmota flaviventris.

2'. Maxillary tooth-rows converging posteriorly; condylobasal length less than 70 mm; front feet with five clawed digits: Cynomys, 3

3. Tip of tail black: Cynomys ludovicianus.

3'. Tip of tail white or light gray: Cynomys gunnisoni.

4. Zygomatic arches nearly parallel to one another: 5

4'. Zygomatic arches convergent anteriorly: 8

5. Total length usually less than 360 mm; P3 vestigial or absent: Tamiasciurus hudsonicus.

5'. Total length usually more than 450 mm; P3 usually well developed: 6

6. Venter orangish, reddish, or buffy: Sciurus niger.

6'. Venter white or black: 7

7. Ears with prominent tufts of hair on ends; usually five cheek teeth in upper tooth-row: Sciurus aberti.

7'. Ears without tufts; usually four cheek teeth in upper tooth-row: Sciurus arizonensis.

8. Sides of head striped; posterior border of zygomatic process of maxillary opposite P3: Tamias, 9

8'. Sides of head not striped; posterior border of zygomatic process of maxillary opposite Ml: 13

9. Dorsal stripes obscure, not clearly delineated: Tamias dorsalis.

9'. Dorsal stripes clearly marked: 10

10. Condylobasal length less than 30.5 mm; hindfoot usually 32 mm or less; upper lip buffy: Tamias minimus.

10'. Condylobasal length more than 31 mm; hindfoot usually 33 mm or more; upper lip whitish: 11

11. Hind feet grayish dorsally; in Gallinas, Capitan, Sacramento, and Guadalupe mountains: Tamias canipes.

11'. Hind feet buffy dorsally; not distributed as above: 12

12. Neck with grayish dorsal wash; south of U.S. 66 and west of Rio Grande: Tamias cinereicollis.

12'. Neck without grayish wash; not distributed as above: Tamias quadrivittatus.

13. Dorsal pattern incorporating some continuous stripes: 14

13'. Dorsal pattern spotted or mottled: 18

14. Dorsal pattern of stripes and rows of spots: Spermophilus tridecemlineatus.

14'. Dorsal pattern of two white stripes; not spots: 15

15. Tail brownish ventrally, longer than 85 mm: Spermophilus lateralis.

15'. Tail whitish, grayish, or blackish ventrally, less than 85 mm: 16

16. Tail dark below: Ammospermophilus harrisii.

16'. Tail whitish below: 17

17. East of Rio Grande: Ammospermophilus interpres.

17'. West of Rio Grande: Ammospermophilus leucurus.

18. Tail long and bushy, more than 135 mm; mottled grayish dorsally: Spermophilus variegatus.

18'. Tail shorter-haired, less than 135 mm; spotted dorsally: 19

19. Spots arranged in many rows: Spermophilus mexicanus.

19'. Spots irregularly arranged: Spermophilus spilosoma.

Key slightly modified from Findley (1987).


Last Update: 4 Jan 2008