1. Total number of teeth, 30 or 28; muzzle short and broad; claws retractile: Felidae, 2
1'. Total number of teeth, 32 or more; claws not retractile, or only partly so: 4
2. Tail more than 30 percent of total length; 3 upper premolars: 3
2'. Tail less than 30 percent of total length; 2 upper premolars: Lynx rufus
3. Dorsal color uniform: Puma concolor
3'. Dorsal color spotted: Panthera onca
4. Hindfoot with 4 toes: Canidae, 5
4'. Hindfoot with 5 toes: 10
5. Postorbital process thick, convex dorsally; condylobasal length greater than 160 mm: Canis, 6
5'. Postorbital process thin, concave dorsally; condylobasal length less than 150 mm: 7
6. Condylobasal length usually more than 210 mm; with mandibles articulated and jaws closed, tips of upper canines do not usually reach a line connecting mental foramina: Canis lupus
6'. Condylobasal length usually less than 190 mm; with mandible articulated and jaws closed, tips of upper canines extend below line connecting mental foramina: Canis latrans
7. Temporal ridges converge posteriorly in a U-shape; a step on ventral margin of dentary in front of angular process; a dorsal black stripe on tail: Urocyon cinereoargenteus
7'. Temporal ridges converge posteriorly in a V-shape; no step on ventral margin of dentary; no dorsal black stripe on tail: 8
8. Tail tip white; posterior surface of ear pinnae black; condylobasal length more than 130 mm: Vulpes vulpes
8'. Tail tip black; posterior surface of pinnae brownish; condylobasal length less than 120 mm: 9
9. Ear greater than 75 mm from notch; auditory bullae large: Vulpes macrotis
9'. Ear less than 75 mm from notch; auditory bullae small: Vulpes velox
10. Tail shorter than hindfoot; total length of adults 1,200 mm or more; 42 or fewer teeth: Ursidae, 11
10'. Tail longer than hindfoot; total length of adults less than 1,200 mm; 40 or fewer teeth: 12
11. Front claws approximately same length as hind ones; no hump at shoulder; second upper molar (last tooth in row) widest near its midpoint; maxillary tooth-row less than 110 mm: Ursus americanus
11'. Front claws obviously longer than hind ones; conspicuous hump at shoulder; second upper molar widest near front; maxillary toothrow more than 110 mm: Ursus arctos
12. Tail usually ringed; 40 teeth; no anal scent glands: Procyonidae, 13
12'. Tail never ringed; less than 40 teeth; anal scent glands present: 15
13. Fourth upper premolar bladelike: Bassariscus astutus
13'. Fourth upper premolar molariform: 14
14. Basilar length of skull more than 115 mm; total length more than 1,000 mm; rostrum and snout elongate and tubular: Nasua nasua
14'. Basilar length of skull less than 115 mm; total length less than 1,000 mm; rostrum not markedly elongate or tubular: Procyon lotor
15. Dorsal coloration black and white; posterior border of hard palate not extending appreciably behind last molars: Mephitidae, 16
15'. Dorsal coloration not black and white; posterior border of hard palate extending appreciably behind last molars: Mustelidae, 19
16. Snout with an enlarged hairless rooting area; two upper premolars on each side; total teeth, 32: Conepatus leuconotus
16'. Snout not modified as above; three upper premolars on each side; total teeth, 34: 17
17. Back with four or more lines of broken white stripes or spots; length of skull less than 60 mm: Spilogale gracilis
17'. Back black, or with continuous white stripes; length of skull more than 60 mm: 18
18. Tail length more than that of head and body; white stripes variable, often nearly absent; bullae somewhat enlarged: Mephitis macroura
18'. Tail length less than that of head and body; white stripes usually prominent; bullae not enlarged: Mephitis mephitis
19. Premolars 4/4: Martes americana
19'. Premolars 2 to 4/3: 20
20. Foot rounded; toes webbed; premolars 4/3; upper molar nearly square; total length more than 840 mm: Lutra canadensis
20'. Foot not round; toes not webbed; premolars fewer than 4/3; upper molar not square: 21
21. Body stout; white stripe on head; foreclaws 30 mm or longer; condylobasal length more than 110 mm: Taxidea taxus
21'. Body slender; no white stripe on head; foreclaws less than 20 mm; condylobasal length less than 80 mm 22
22. Hindfoot greater than 55 mm; condylobasal length greater than 6O mm: 23
22'. Hindfoot less than 50 mm; condylobasal length less than 55 mm: 24
23. Color of body and tail yellowish; tip of tail, face mask, and feet black: Mustela nigripes
23'. Color uniformly medium to dark brown; tail, face, and feet not distinctively colored: Mustela vison
24. Venter white to sulphur-yellow in summer; condylobasal length less than 35 mm: Mustela erminea
24'. Venter orangish brown in summer; condylobasal length more than 40 mm: Mustela frenata
Key slightly modified from Findley (1987).
Last Update: 4 Jan 2007