Dichotomous Key to Mammals of Southwest Ohio

1a. Incisor teeth or holes from them arepresent in the upper jaw. Go to 2.

1b. Incisor teeth or holes from them areabsent in the upper jaw. Go to 8.

2a. (From 1a) Space between upperincisors and molars is larger than thewidest molar; upper canine teeth areoften absent. Go to 3.

2b. (From 1a) Space between upperincisors and molars is smaller than thewidest molar; upper canine teeth arepresent. Go to 5.

3a. (From 2a) Three incisors in each half ofthe upper jaw; length of skull is morethan 228 mm (9 inches). Domesticanimal; horse or mule.

3b. (From 2a) One or two incisors in eachhalf of the upper jaw; length of skull isless than 152 mm (6 inches). Go to 4.

4a. (From 3b) Two incisors in each half ofthe upper jaw, the smaller one directlybehind the larger one; bony network onthe side of the face is in front of the eyesocket; 28 total teeth. Easterncottontail rabbit (Sylvaligusfloridanus).

4b. (From 3b) One incisor in each half ofthe upper jaw; no bony network on theside of the face in front of the eyesocket; 16-22 total teeth. Go to 9.

5a. (From 2b) First upper incisor is greatlyenlarged. Short-tailed shrew (Blarinabrevicauda).

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5b. (From 2b) First upper incisor is notgreatly enlarged. Go to 6.

6a. (From 5b) Five incisors in each half ofthe upper jaw. Opossum (Didelphisvirginiana).

6b. (From 5b) Three incisors in each half ofupper jaw. Go to 7.

7a. (From 6b) Upper canine teeth projectoutward when viewed from the front.Domestic animal; probably pig (Susscrofa).

7b. (From 6b) Upper canine teeth projectstraight downward. Go to 16.

8a. (From 1b) Large space (15 mm [5/8inch] or more in width) in front of theeye socket; antlers sometimes present.White-tailed deer (Odocoileusvirginianus).

8b. (From 1b) No or small space (less than15 mm [5/8 inch] in width) in front ofthe eye socket. Farm animal; cow,goat, or sheep.

9a. (From 4b) 22 total teeth, 12 on top, 10on bottom. Go to 10.

9b. (From 4b) Less than 22 total teeth. Goto 11.

10a. (From 9a) Skull less than 63 mm (2-1/2inches) in length. Eastern graysquirrel (Sciurus carolinensis).

Large space

Five cheek teeth

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10b. (From 9a) Skull more than 73 mm (2-7/8 inches) in length. Woodchuck(Marmota monax).

11a. (From 9b) 20 total teeth, 10 on top, 10on bottom. Go to 12.

11b. (From 9b) Less than 20 total teeth. Goto 14.

12a. (From 11a) Length of skull is 101 mm(4 inches) or more. Beaver (Castorcanadensis).

12b. (From 11a) Length of skull is less than101 mm (4 inches). Go to 13.

13a. (From 12b) Length of skull is 63 mm(2-1/2 inches) or more. Fox Squirrel(Sciurus niger).

13b. (From 12b) Length of skull is less than63 mm (2-1/2 inches). EasternChipmunk (Tamias striatus).

14a. (From 11b) 18 Total teeth, 10 on top, 8on bottom. Meadow jumping mouse(Zapus hudsonius).

14b. (From 11b) 16 total teeth. Go to 15.

15a. (From 14b) Length of skull is morethan 38 mm (1-1/2 inches). Muskrat(Ondatra zibethicus).

15b. (From 14b) Length of skull is less than38 mm (1-1/2 inches). Any of manyspecies of rats, mice, voles, orlemmings.

Five cheek teeth

Four cheek teeth

Four cheek teeth

Three cheek teeth

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16a. (From 8b) Length of skull is 254 mm(10 inches) or more. Black bear (Ursusamericanus).

16b. (From 8b) Length of skull is less than254 mm (10 inches). Go to 17.

17a. (From 16b) 28 total teeth, 14 on top, 14on bottom. Bobcat (Lynx rufus).

17b. (From 16b) Total teeth not 28. Go to18.

18a. (From 17b) 30 total teeth. Domestic cat(Felis domestica).

18b. (From 17b) Total teeth not 30. Go to19.

19a. (From 18b) 40 total teeth, 20 on top, 20on bottom. Raccoon (Procyon lotor).

19b. (From 18b) Total teeth not 40. Go to20.

20a. (From 19b) 42 total teeth, 20 on top, 22on bottom. Go to 21.

20b. (From 19b) 34 total teeth, 16 on top, 18on bottom. Go to 23.

21a. (From 20b) Upper surface of skull has aprominent crest formed by paired ridgesthat converge in the midline. Coyote(Canis latrans) or domestic dog (Canisfamiliarus).

21b. (From 20b) Upper surface of skull issmooth or has paired ridges that, if theyconverge, do so at rear of skull and donot form prominent crest. Go to 22.

22a. (From 21b) Length of skull is 133 mm(5-1/4 inches) or more. Red fox (Vulpesvulpes).

Premolarssometimesmissing

Short face and rounded forehead

4-1/4 – 5 inches 107-127mm

6 3/4 –8 5/8 inches 171-219mm

Postorbital process convex

Prominent crestformed by convergingpaired ridges

5 1/4 –6 1/4 inches 133-158mm

No notch

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22b. (From 21b) Length of skull is less than130 mm (5-1/8 inches). Gray fox(Urocyon cinereoargenteus).

23a. (From 20b) Hard palate (roof of mouth)does not extend beyond last uppermolars. Striped skunk (Mephitismephitis).

23b. (From 20b) Hard palate (roof of mouth)extends beyond last upper molars. Goto 24.

24a. (From 23b) Upper molars are triangular(for molar shape, see picture for 23b).Badger (Taxidea taxus).

24b. (From 23b) Upper molars aredumbbell-shaped. Go to 25.

25a. (From 24b) Length of skull is 50 mm (2inches) or more. Mink (Mustela vison).

25b. (From 24b) Length of skull is less than50 mm (2 inches). Go to 2.

Well-rounded

Molartriangularshaped

Hard palate extendingbeyond molars

Molar dumbbell-shaped

Hard palate extendingbeyond molars

Prominent notch

4 3/4 –5 1/8 inches 120-130mm

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26a. (From 25b) Length of skull is 31-50mm (1-1/4 to 2 inches). Long-tailedweasel (Mustela renata).

26b. (From 25b) Length of skull is less than31 mm (1-1/4 inches). Least weasel(Mustela nivalis).

Source for skull drawings:

Ohio Department of Natural Resources Division of Wildlife’s Life History Notes

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