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Sorex obscurus

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Northern Montane Shrew
(Sorex obscurus)
Range
Taxonomic classification
Order:Eulipotyphla
Suborder:Erinaceota
Family:Soricidae
Subfamily:Soricinae
Tribe:Soricini
Genus:Sorex
Subgenus:Otisorex
Species group:Sorex monticolus group
Binomial details
Sorex obscurus Merriam, 1895

From Woodman (2018): "Phylogenetic analysis of the mitochondrial cytochrome b gene indicated that S. monticola, as considered by Alexander (1996), is not monophyletic but includes three genetically divergent clades (Demboski and Cook, 2001; Shafer and Stewart, 2007)." According to Demboski & Cook (2001), the “northern continental clade" belongs to Sorex obscurus, and the “southern continental clade” belongs to the Southern Montane Shrew (Sorex monticolus), and the "coastal clade" belongs to the Pacific Shrew (Sorex pacificus). Further studies will be needed to fully understand new species boundaries and morphological variation.

Description

A formal species description for this taxon as delineated by Demboski & Cook (2001) does not currently exist. The following descriptions are provided for portions of the range of Sorex monticolus that Demboski & Cook (2001) subsumed under this taxon.

From Verts & Carraway (1998), describing two geographic variants that were described under S. monticolus, but are now presumed to be S. obscurus based on molecular studies by Demboski & Cook (2001): "[in northwestern Oregon] is blackish brown on the dorsum and light brown on the venter; the bases of the hairs are neutral very dark-gray. The tail is distinctly bicolored, blackish brown above, pinkish gray below; the flank glands are covered with pale brown bristles. The dorsal pelage of S. m. obscurus [northeastern part of the state] has yellow overtones—medium brown to medium yellowish-brown; the venter is white. The tail is indistinctly bicolored, medium brown above grading to white below; the flank glands have white bristles (Carraway, 1990)."

From Naughton (2012) for Canada: "very dark grey or greyish brown to brown (often with reddish or yellowish overtones) on their back and sides (sides may be slightly paler), with a somewhat lighter belly of silver to smoky grey to buffy brown. Interior populations in British Columbia tend to be brownish, but coastal populations may be almost black on the upper surfaces, especially in winter when the pelage is darker and greyer than in summer. Their long tail is bicoloured, dark brown above with a pinkish-grey or pale brown underside, and does not have a black tip. The upper surfaces of the feet are pale brown or grey brown."

External measurements

Length measurements are in millimeters (mm) and weight measurements are in grams (g), unless stated otherwise. If available, the sample size (n=) is provided. If a range is not provided and n= is not given, then the listed measurement represents an average.

Part of range Reference Total length Tail length Hindfoot length Ear length Mass
Canada Naughton (2012) 93–140 35–68 10–18 4–10 3.7–13.0 (avg 6–7)
Canada Wilson & Ruff (editors, 1999) 95–139 30–62 4.4–10.2
Oregon (eastern) Verts & Carraway (1998) 85–127 35–45 10–13 2.4–6.1
Oregon (Hood River Co.) Verts & Carraway (1998) 105–127 41–55 12–16 3.6–9.4


Color variation

This section shows some of the color variation present in Sorex obscurus. The location is provided for reference only. The individual shown does not necessarily represent the only color variant within the local population.

Skull characters

Sorex obscurus skull characters
units in mm
Skull
Condylobasal length:16.1–17.7 (Hennings & Hoffman, 1977); 16.1–19.2 (Junge & Hoffman, 1981)
Postmandibular canal:Absent
Shape:Skull somewhat slightly flattened
Dental
Upper unicuspids:5
Unicuspid notes:U3<U4
Tines present:Yes
Tine size:Small-medium
Tine position:Below upper limit of pigment on upper incisors
Shape upper incisors:Diverging

  • Lateral view of the skull of Sorex obscurus. Lower jaw is not shown. Long scale bar represents 1 cm; short scale bar represents 1 mm.
  • Unicuspids of Sorex obscurus, scale is 1 mm.
  • Upper incisors of Sorex obscurus, Denali Borough, Alaska, scale is 1 mm.
  • Upper incisors of Sorex obscurus, Denali Borough, Alaska, scale is 1 mm.

Similar species

Distinguishing between the Southern Montane Shrew (Sorex monticolus) and Sorex obscurus in the field may require genetic testing. Currently, the boundaries of Sorex monticolus and Sorex obscurus are not well understood in eastern Idaho, southeastern Wyoming, and northwestern Colorado. Further studies are needed to fully understand species boundaries and morphological variation.

  • Distribution of Southern Montane Shrew (Sorex monticolus) as defined by Demboski & Cook (2001).
  • Distribution of Sorex obscurus as defined by Demboski & Cook (2001).

References

Alexander LF. 1996. A morphometric analysis of geographic variation within Sorex monticolus. University of Kansas Natural History Museum Miscellaneous Publication (88): 1-54.

Carraway LN. 1990. A morphologic and morphometric analysis of the "Sorex vagrans species complex" in the Pacific Coast region. Special Publications, The Museum, Texas Tech University 32:1-76.

Demboski JR, Cook JA. 2001. Phylogeography of the dusky shrew, Sorex monticolus (Insectivora, Soricidae): insight into deep and shallow history in northwestern North America. Molecular Ecology 10(5): 1227-1240.

Hennings D. 1970. Systematics of the Sorex vagrans-obscurus complex revisited. Graduate Student Theses, Dissertations, & Professional Papers. 6564. https://scholarworks.umt.edu/etd/656

Hennings D, Hoffmann RS. 1977. A review of the taxonomy of the Sorex vagrans species complex from western North America. Occasional Papers of the Museum of Natural History, University of Kansas 68:1-35.

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

Naughton D. 2012. The natural history of Canadian mammals. Toronto (ON, CA): University of Toronto Press.

Verts BJ, Carraway LN. 1998. Land mammals of Oregon. Berkeley (CA, USA): University of California Press.

Wilson DE, Ruff S, editors. 1999. The Smithsonian Book of North American Mammals. Washington D.C. (USA): Smithsonian Institution Scholarly Press.

Woodman N. 2012. Taxonomic status and relationships of Sorex obscurus parvidens, from California. Journal of Mammalogy 93(3): 826-838.

Woodman N. 2018. American Recent Eulipotyphla: nesophontids, solenodons, moles, and shrews in the New World. Washington D.C. (USA): Smithsonian Institution Scholarly Press. https://doi.org/10.5479/si.1943-6696.650.

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