Key to Lower Jaws in Owl Pellets in the Pacific Northwest

1. A.	Relatively large (and uncommon), length from back to tip of incisors over 35 mm, no coronoid process, angle of jaw rounded, (Fig. 7), cheek tooth row about 10 mm	Sylvilagus floridanus
B.	Jaw smaller, under 35 mm in length, coronoid process present (but small in some), cheek tooth row less that 8 mm.	Go to 2.

2. A.	With a distinct gap, diasthema, between a single large, curved incisor tooth and 3 or 4 cheek teeth (Fig. 8)	Go to 3.
B.	Without a large gap between teeth, first incisor not greatly larger that other teeth or, if larger, not an arc (Fig. 9).	Go to 8.

3. A.	With three cheek teeth, tooth pattern complex.	Go to 4.
B.	With 4 cheek teeth, pattern 1 or 2 ovals (Fig. 8, 10).	Northern Pocket Gopher Thomomys talpoides And related species.

4. A.	Jaw length, including incisor, over 22 mm, about 7 mm from base of incisor to base of 1^st cheek tooth	Rattus sp.
B.	Jaw under 21 mm (18 without incisor), about 5 mm or less from base of incisor to 1^st cheek tooth.	Go to 5.

5. A.	Cheek teeth flat crowned with a series of loops and triangles (Fig. 5, 6).	Go to 6.
B.	Cheek teeth either with obvious cones or with unevenly worn surface.	Go to 7.

6. A.	Cheek tooth row about 6 mm in length.	Microtus townsendii
B.	Cheek tooth row about 5 mm in length.	Microtus oregoni

7. A.	Coronoid process well developed, extending back over 1 mm; cheek tooth row about 4 mm in length; angular process broad at the back, over 3 mm wide with distinct lateral projection.	Jumping Mouse, Zapus sp.
B.	Coronoid process reduced, projecting upward rather than backward (Fig. 12).	Go to 8.

8. A.	Cheek tooth row length about 3.5 mm, 12-14 mm from base of incisors to rear of jaw.	Deer Mouse, Peromyscus maniculatus
B.	Cheek tooth row about 3 mm in length, about 11 mm from base of incisors to rear of jaw.	House Mouse, Mus musculus

9. A.	Without distinctly enlarged canine teeth, (Fig. 3).	Go to 10.
B.	With distinctly enlarged canine teeth or “fangs” (Fig. 8).	Go to 14.

10. A.	Teeth reddish brown at tips, 1^st incisor, if present, elongated with several rounded cones, nearly as long as rest of tooth row, directed forward and thus like an extension of the jaw.	Shrews, genus Sorex Go to 11.
B.	Teeth white or gray but not reddish at tips, 1^st incisor like other teeth in size.	Moles, genus Scapanus Go to 12.

11. A.	Total length of lower jaw about 7 mm with 1^st incisor, 1^st incisor 2-3 mm in length.	Wandering Shrew, Sorex vagrans
B.	Total length of lower jaw about 12-13 mm, 1^st incisor 3-4 mm in length.	Pacific Water Shrew, Sorex bendirii

12. A.	Total length about 14 mm, tooth row about 9 mm.	Shrew mole, Neurotrichus gibbsii
B.	Total length over 20 mm.	Go to 13.

13. A.	Total length about 23 mm, tooth row about 13 mm.	Coast Mole, Scapanus orarius
B.	Total length about 23 mm, tooth row about 17 mm.	Townsend’s Mole, Scapanus townsendii

14. A.	Last cheek tooth very small, less than 50% of previous tooth, 2^nd to last the largest, very elongated, about the length of the 3 preceding cheek teeth, with outer surface smooth.	Weasels, genus Mustela
B.	Last cheek tooth at least 50% of preceding tooth, 2^nd to last may be the largest but still about the size of the others next to it, its outer surface with grooves.	Bats, genera Myotis, Eptesicus, or Plecotus