Key to the Long-tailed Shrews of the US and Canada

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This key to the long-tailed shrews (genus Sorex) of the United States and Canada is based on Junge and Hoffman (1981). It was modified by Laura Steger to accommodate recent taxonomic revisions.

Junge, J.A. and Hoffman, R.S., 1981. An annotated key to the long-tailed shrews (Genus Sorex) of the United States and Canada with notes on middle American Sorex. Occasional Papers of the Museum of Natural History, The University of Kansas, Lawrence Kansas. Number 94; Pages 1-48. Link

1

Usually no post-mandibular foramen (Fig. 1a); or if present, small and often only on one mandible. Unicuspids with a ridge, usually pigmented, on the face, running from apex to cingulum, sometimes ending in a pigmented cusplet (Fig. 2a) . . . . . subgenus Otiosorex

Usually a well-developed post-mandibular foramen (Fig. 1b). No pigmented ridge on lingual face of the unicuspids (Fig. 2b) . . . . . subgenera Sorex and incertae sedis

Figure 1. Arrow points to the location of the post-mandibular canal. Modified from Junge and Hoffman (1981).
Figure 2. Ventro-lateral view of rostrum, showing occlusal surface of unicuspid teeth; a) with pigmented ridge, and b) lack of pigmented ridge. Borrowed from Junge and Hoffman (1981).

2

Return to couplet #1

Unicuspid toothrow "crowded", only three unicupsids easily visible in lateral (buccal) view; U3 tiny, disc-like; U4 of normal size and shape; U5 minute. Accessory medial tine (projection resembling a prong) on the anterior surface of first upper incisor (I1) is relatively large and long. Condylobasal (CB) length 12.7–15.8 mm. Distribution boreal and montane. . . . . . 4

Four or five unicuspids visible from side; U3 equal to or larger than U4, or if smaller, of normal shape rather than disc-like. Medial tine, if present, not as above. . . . . . 3

3

Return to couplet #2

U3 and U4 usually equal in size, or if different U3 slightly smaller; anterior edges of zygomatic plate posterior to plane separating M1 and M2; rostrum unusually long and narrow. Unicuspids widely spaced, relatively narrow; ridge on lingual face of unicuspids often lacking pigment.... Sorex dispar

Not as above. . . . . . 5

4

Return to couplet #2

Distribution: Sorex hoyi was split in 2020 by Hope et al. Western populations of S. hoyi are now referred to as S. eximius.....Sorex eximius

Unicuspids of Sorex eximius
Upper incisors of Sorex eximius
Range of Sorex eximius

Distribution: Eastern US and Canada.....Sorex hoyi

Unicuspids of Sorex hoyi. Note that this is an old individual and the teeth are worn.
Upper incisors of Sorex hoyi.
Range of Sorex hoyi

5

Return to couplet #3

U3 usually distinctly smaller than U4, sometimes subequal. . . . . . 6

U3 usually larger than U4, sometimes subequal. Sorex fumeus and Sorex cinereus group. . . . . . 14

6

Return to couplet #5

Skull large, condylobasal (CB) length usually more than 19.0 mm. . . . . . 7

Skull medium to small, condylobasal (CB) length usually less than 19.0 mm. . . . . . 9

7

Return to couplet #6

Largest North American Sorex, CB length 20.8–23.8 mm; skull and teeth robust; rostrum relatively long, broad, distinctly downcurved; medial tine may be large, placed high on face of I1, pigmented; pigmented area of incisor may curve up to meet that of tine. Distribution, northwest Pacific coast....Sorex bendirii
Medial tine absent or, if present, small and placed low on medial face of I1; somewhat smaller, CB length 19.0–22.8 mm; skull and teeth not so robust, rostrum not downcurved. . . . . . 8

8

Return to couplet #7

Small medial tines present on I1; unicuspids longer than wide in ventral view. Distribution, boreo-montane. . . . . . 26

No medial tines present on I1; unicuspids wider than long to approximately quadrate in ventral view. Distribution, Pacific coast....Sorex pacificus

9

Return to couplet #6

Medial tine begins above main pigmented area of first incisors. . . . . . 10

Medial tine contained entirely within pigmented area of first incisor. . . . . . 11

No medial tine on first incisors....Sorex sonomae

10

Return to couplet #9

Skull larger, CB length 15.5–17.5 mm. Usually distinct unpigmented gap between upper pigmented area of first incisor and pigmented medial tine. Rostrum relatively long and narrow, cranium relatively inflated. Unicuspids quadrate or longer than wide; U1 and U2 more robust, bulbous; U3 definitely smaller than U4. Distribution western North America....Sorex vagrans

Skull smaller, CB length 13.8–15.6 mm (except S. l. fisheri, 15.4–16.4 mm). Usually no definite gap between pigmented areas of incisor and medial tine. Rostrum relatively short and broad, cranium relatively flat. Unicuspids wider than long; U1 and U2 less robust, not bulbous; U3 and U4 sometimes subequal. Distribution, southeastern North America....Sorex longirostris

11

Return to couplet #9

CB length 15.4 mm or more; in ventral view, U3 usually distinctly smaller than U4. . . . . . 12

CB length 15.3 mm or less; U3 and U4 may sometimes appear subequal in ventral view. . . . . . 13

12

Return to couplet #11

Condylobasal length 16.1–19.2 mm; cranium relatively inflated. Unicuspids become appressed posteriorly, U5 against P4, with no noticeable gap between U5 and P4 along medial edge. Distribution, northwestern montane and boreal North America (mostly north and east of S. ornatus). . . . . . 27 (Sorex monticolus or Sorex obscurus)

Condylobasal length 15.4–17.0 mm; cranium relatively flat. Unicuspid toothrow less appressed posteriorly, so that there is a distinct triangular gap between U5 and P4 along the medial edge. Distribution, California, south from the San Francisco Bay area, west of the crest of the Sierra Nevada, Santa Catalina Island, and Baja California (mostly south and west of S. monticolus)....Sorex ornatus

13

Return to couplet #11

Condylobasal length 13.8–14.8 mm; cranium extremely flat. Distribution, discontinuous, mostly montane, in Rocky Mountains, Colorado Plateau, and western Great Plains....Sorex nanus

Condylobasal length 14.5–15.3 mm; cranium less flat. Distribution, southern Great Basin....Sorex tenellus

14

Return to couplet #5

Skull large, CB length 17.8–19.0 mm; palate broad; maxillary breadth greater than 4.6 mm; cranium usually flattened to some degree, sometimes extremely so. Unicuspids wider than long; ridge on lingual face of unicuspid often lacking pigment. Small post-mandibular foramen sometimes present, at least on one mandible. Distribution, northeastern United States and southeastern Canada....Sorex fumeus

Skull small to moderate, CB length 13.8–17.0 mm, the larger species with inflated braincase. Maxillary breadth less than 4.6 mm; unicuspids relatively narrow, quadrate to longer than wide. . . . . . 15

15

Return to couplet #14

Extremely small, CB length 13.8–14.6 mm, skull relatively flat. Unicuspid teeth closely appressed, rostrum relatively short. When sympatric with S. cinereus and S. haydeni, this is the smaller shrew. Distribution, Columbia plateau to western Great Plains....Sorex preblei

Usually larger, CB length usually 14.6–17.0 mm (but to 14.1 mm in some populations); unicuspids well-spaced; rostrum relatively more elongate. . . . . . 16

16

Return to couplet #15

Found only on islands in the Bering Strait or Sea. . . . . . 17

Not as above. . . . . . 18

17

Return to couplet #16

Known only from St. Paul, Pribilof Islands....Sorex pribilofensis

Known only from St. Lawrence Island....Sorex jacksoni

18

Return to couplet #16

Usually smaller, CB length 14.1–15.6 mm; unicuspid toothrow relatively shorter, M2-M2 width relatively larger; ratio of length of unicuspid toothrow to M2-M2 width usually less than 0.6. . . . . . 19

Usually larger, CB length 14.6–17.0 mm; unicuspid toothrow relatively longer, width of M2-M2 relatively smaller; ratio of unicuspid toothrow length to M2-M2 width usually greater than 0.6. . . . . . 20

19

Return to couplet #18

Restricted to northern Great Plains area, south of 55 degrees N Latitude....Sorex haydeni

Restricted to tundra of extreme northwestern North America, north of 58 degrees N Latitude....Sorex cinereus (in part)

20

Return to couplet #18

CB length 14.6–15.2 mm; cranium relatively flat; rostrum broad, and unicuspid toothrow slightly shorter. Distribution, southern Pennsylvania, Delaware, Maryland, northeastern Virginia....Sorex fontinalis

CB length 15.0–17.0 mm; cranium inflated; rostrum narrow, and unicuspid toothrow slightly longer. . . . . . 21

21

Return to couplet #20

Found only in central Sierra Nevada....Sorex lyelli

Found throughout much of northern and middle latitudes of North America....Sorex cinereus (in part)

22

Return to couplet #1

U3 usually smaller than U4. Small medial tine high on anterior face of I1. Distribution, Pacific Coast....Sorex trowbridgii

Unicuspids of Sorex trowbridgii
Upper incisors of Sorex trowbridgii
Range of Sorex trowbridgii

U3 usually larger than U4. . . . . . 23

23

Return to couplet #22

No medial tine on anterior face of I1. Palate unusually broad; CB length 15.0–16.6 mm. Distribution, Columbia Plateau and Great Basin to western Great Plains....Sorex merriami

Unicuspids of Sorex merriami, modified from Diersing & Hoffmeister (1977).
Upper incisors of Sorex merriami. Borrowed from Diersing & Hoffmeister (1977).
Range of Sorex merriami.

Medial tine on anterior face of I1; palate not usually broad. . . . . . 24

24

Return to couplet #23

CB length 16.5 or less, maxillary toothrow 6.0–6.4 mm. Described only from mountains of Arizona, New Mexico, and adjacent Mexico....Sorex arizonae

Upper incisors of Sorex arizonae.
Unicuspids of Sorex arizonae. Borrowed from Diersing & Hoffmeister (1977). The third upper unicuspid is equal to or larger than the fourth.
Range of Sorex arizonae

Skull length 17.0 mm or more; maxillary toothrow 6.0–7.8 mm. Found in upper Great Lakes, northeastern Great Plains, Canada, and Alaska. . . . . . 25

25

Return to couplet #24

CB length 18.3–20.3 mm; maxillary toothrow 6.8–7.8 mm. Unicuspid row appears uncrowded; unicuspids robust and appear bulbous in ventral view. Distribution, upper Great Lakes, northeastern Great Plains, and Canada, except NW Yukon and extreme NW British Columbia....Sorex arcticus

Upper incisors of Sorex arcticus, scale is 1 mm
Upper unicuspids of Sorex arcticus, scale is 1 mm
Range of Sorex arcticus

CB length 17.0–18.5 mm; maxillary toothrow 6.0–6.9 mm. Unicuspids appear crowded, less robust, not bulbous. Distribution, Alaska, Yukon, and extreme NW British Columbia....Sorex tundrensis tundrensis