Dichotomous Key to Mammals of Southwest Ohio 1a. Incisor teeth or holes from them are present in the upper jaw. Go to 2. 3a. (From 2a) Three incisors in each half of the upper jaw; length of skull is more than 228 mm (9 inches). Domestic animal; horse or mule. 3b. (From 2a) One or two incisors in each half of the upper jaw; length of skull is less than 152 mm (6 inches). Go to 4. 1b. Incisor teeth or holes from them are absent in the upper jaw. Go to 8. 4a. (From 3b) Two incisors in each half of the upper jaw, the smaller one directly behind the larger one; bony network on the side of the face is in front of the eye socket; 28 total teeth. Eastern cottontail rabbit (Sylvaligus floridanus). 2a. (From 1a) Space between upper incisors and molars is larger than the widest molar; upper canine teeth are often absent. Go to 3. 4b. (From 3b) One incisor in each half of the upper jaw; no bony network on the side of the face in front of the eye socket; 16-22 total teeth. Go to 9. 2b. (From 1a) Space between upper incisors and molars is smaller than the widest molar; upper canine teeth are present. Go to 5. 5a. (From 2b) First upper incisor is greatly enlarged. Short-tailed shrew (Blarina brevicauda). 1 of 6
5b. (From 2b) First upper incisor is not greatly enlarged. Go to 6. 6a. (From 5b) Five incisors in each half of the upper jaw. Opossum (Didelphis virginiana). 8a. (From 1b) Large space (15 mm [5/8 inch] or more in width) in front of the eye socket; antlers sometimes present. White-tailed deer (Odocoileus virginianus). Large space 8b. (From 1b) No or small space (less than 15 mm [5/8 inch] in width) in front of the eye socket. Farm animal; cow, goat, or sheep. 6b. (From 5b) Three incisors in each half of upper jaw. Go to 7. 7a. (From 6b) Upper canine teeth project outward when viewed from the front. Domestic animal; probably pig (Sus scrofa). 9a. (From 4b) 22 total teeth, 12 on top, 10 on bottom. Go to 10. 9b. (From 4b) Less than 22 total teeth. Go to 11. 10a. (From 9a) Skull less than 63 mm (2-1/2 inches) in length. Eastern gray squirrel (Sciurus carolinensis). 7b. (From 6b) Upper canine teeth project straight downward. Go to 16. Five cheek teeth 2 of 6
10b. (From 9a) Skull more than 73 mm (2-7/8 inches) in length. Woodchuck (Marmota monax). 13b. (From 12b) Length of skull is less than 63 mm (2-1/2 inches). Eastern Chipmunk (Tamias striatus). Five cheek teeth 11a. (From 9b) 20 total teeth, 10 on top, 10 on bottom. Go to 12. 14a. (From 11b) 18 Total teeth, 10 on top, 8 on bottom. Meadow jumping mouse (Zapus hudsonius). 11b. (From 9b) Less than 20 total teeth. Go to 14. 12a. (From 11a) Length of skull is 101 mm (4 inches) or more. Beaver (Castor canadensis). 14b. (From 11b) 16 total teeth. Go to 15. Four cheek teeth 15a. (From 14b) Length of skull is more than 38 mm (1-1/2 inches). Muskrat (Ondatra zibethicus). 12b. (From 11a) Length of skull is less than 101 mm (4 inches). Go to 13. Three cheek teeth 13a. (From 12b) Length of skull is 63 mm (2-1/2 inches) or more. Fox Squirrel (Sciurus niger). Four cheek teeth 15b. (From 14b) Length of skull is less than 38 mm (1-1/2 inches). Any of many species of rats, mice, voles, or lemmings. 3 of 6
16a. (From 8b) Length of skull is 254 mm (10 inches) or more. Black bear (Ursus americanus). 19b. (From 18b) Total teeth not 40. Go to 20. 20a. (From 19b) 42 total teeth, 20 on top, 22 on bottom. Go to 21. 20b. (From 19b) 34 total teeth, 16 on top, 18 on bottom. Go to 23. Premolars sometimes missing 16b. (From 8b) Length of skull is less than 254 mm (10 inches). Go to 17. 21a. (From 20b) Upper surface of skull has a prominent crest formed by paired ridges that converge in the midline. Coyote (Canis latrans) or domestic dog (Canis familiarus). 6 3/4 8 5/8 inches 171-219mm 17a. (From 16b) 28 total teeth, 14 on top, 14 on bottom. Bobcat (Lynx rufus). Short face and rounded forehead Postorbital process convex 17b. (From 16b) Total teeth not 28. Go to 18. 18a. (From 17b) 30 total teeth. Domestic cat (Felis domestica). 18b. (From 17b) Total teeth not 30. Go to 19. 19a. (From 18b) 40 total teeth, 20 on top, 20 on bottom. Raccoon (Procyon lotor). 21b. (From 20b) Upper surface of skull is smooth or has paired ridges that, if they converge, do so at rear of skull and do not form prominent crest. Go to 22. 22a. (From 21b) Length of skull is 133 mm (5-1/4 inches) or more. Red fox (Vulpes vulpes). 5 1/4 6 1/4 inches 133-158mm Prominent crest formed by converging paired ridges 4-1/4 5 inches 107-127mm 4 of 6 No notch
22b. (From 21b) Length of skull is less than 130 mm (5-1/8 inches). Gray fox (Urocyon cinereoargenteus). 4 3/4 5 1/8 inches 120-130mm 24a. (From 23b) Upper molars are triangular (for molar shape, see picture for 23b). Badger (Taxidea taxus). Prominent notch 23a. (From 20b) Hard palate (roof of mouth) does not extend beyond last upper molars. Striped skunk (Mephitis mephitis). 24b. (From 23b) Upper molars are dumbbell-shaped. Go to 25. Molar dumbbellshaped Well-rounded Hard palate extending beyond molars 25a. (From 24b) Length of skull is 50 mm (2 inches) or more. Mink (Mustela vison). 23b. (From 20b) Hard palate (roof of mouth) extends beyond last upper molars. Go to 24. 25b. (From 24b) Length of skull is less than 50 mm (2 inches). Go to 2. Molar triangular shaped Hard palate extending beyond molars 5 of 6
26a. (From 25b) Length of skull is 31-50 mm (1-1/4 to 2 inches). Long-tailed weasel (Mustela renata). 26b. (From 25b) Length of skull is less than 31 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 6 of 6