Mictomys borealis
Until recently, Mictomys borealis was considered a species in the genus Synaptomys. Hope et al. (2023) provides multiple lines of evidence that supports the recognition of northern bog lemmings as Mictomys borealis, distinct at the generic level from Synaptomys.
| Northern Bog Lemming
(Mictomys borealis) | |
|---|---|
| Range | |
 | |
| Taxonomic classification | |
| Order: | Rodentia |
| Suborder: | Supramyomorpha |
| Infraorder: | Myomorphi |
| Superfamily: | Muroidea |
| Family: | Cricetidae |
| Subfamily: | Arvicolinae |
| Tribe: | Lemmini |
| Genus: | Mictomys |
| Binomial details | |
| Mictomys borealis (J. Richardson, 1828) | |
| Other resources | |
| Full taxonomic details at MDD | |
Description
From Howell (1927) for the Athabaska-Mackenzie region of Canada from Great Bear Lake south to near Edmonton, and eastward (provisionally) to Lake Winnipeg: "The dorsal coloration is very rich and dark, close to the Argus brown of Ridgway, and plentifully mixed with black-tipped hairs. This richness of color is most pronounced on the rump, the anterior portion of the body often being duller, slightly grizzled, and a trifle paler. The plumbeous of the under surface of the specimens at hand is rather dark and without appreciable tinge of buff. That tail is distinctly bicolor and the feet vary from grayish to almost black."
From Howell (1927) for the Hudsonian Zone in Alaska and south to central British Columbia to the eastward of the coast district: "In the case of Yukon animals, the dorsal coloration is close to the Brussels brown of Ridgway, with the usual admixture of blackish hairs. Tail, quite sharply bicolor."
From Howell (1927) for the coastal strip in the Canadian Zone from the Alexander Archipelago southward to the northern border of the United States: "In coloration, ranging from skins that are a perfect match for the brightest, brownest dalli, to others that can not be told from gray and grizzled specimens of chapmani, but the warmer tone of color seems to be somewhat the more prevalent and to be more typical of the unworn condition of pelage."
From Howell (1927) for the Canadian Zone in the northern New England states from the type locality north to include New Brunswick and the portion of Quebec east and south of the St. Lawrence River: "Dorsal coloration close to the Prout brown of Ridgway, which is most intense upon the rump; anteriorly duller, grayer, and more grizzled. Tail, distinctly bicolor."
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) | 102–150 | 15–30 | 14–22 | 11–15 | 21.7–48.0 |
| Minnesota | Hazard (1982) | 110–122 (n=3) | 18–37 (n=3) | 18–19 (n=3) | 13 (n=1) |
Skull
The mandibular molars are formed entirely of transverse, wedge-shaped loops, four in the first (including anterior "trefoil"), and three in the second and third. These differ in pattern from Synaptomys in the absence of an outer closed triangle on each mandibular molar. Howell (1927) noted that "the incisors are pale in color, especially upon the outer edges, relatively light, and the grooves of the upper ones are not so close to the outer borders" as in Synaptomys. Howell (1927) also noted that "the lower incisors are very long, slender, and exceedingly sharply pointed."
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Lateral view of the skull of Mictomys borealis. -
Dorsal view of the skull of Mictomys borealis. -
Ventral view of the skull of Mictomys borealis. -
The upper incisors of Mictomys borealis are grooved. -
Upper molars of Mictomys borealis. -
Lower molars of Mictomys borealis. The third lower molar (m3) has 3 closed loops. The mandibular molars lack closed triangles on the lingual side (Naughton, 2012). -
Enamel pattern of the upper (top) and lower (bottom) molars of Mictomys borealis. Borrowed from Howell (1927).
Similar species
Differences between Synaptomys cooperi and Mictomys borealis are given in the key below, which is based on Linzey (1983) and Naughton (2012).
Mammae six; each mandibular (lower jaw) molar has a closed triangle on the labial (outer) side; the third mandibular molar (m3) has 4 closed triangles; mandibular incisors heavy; palate ending posteriorly with a broad blunt median projection...................... Southern Bog Lemming (Synaptomys cooperi)
Mammae eight; each mandibular (lower jaw) molar lacks a closed triangle on the labial (outer) side; the third mandibular molar (m3) has 3 closed loops; mandibular incisors relatively slender; palate ending posteriorly with a sharply pointed median projection... Mictomys borealis
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Dorsal view of the skull of Synaptomys cooperi. -
Dorsal view of the skull of Mictomys borealis. -
Lower molars of Synaptomys cooperi. Each mandibular molar has a small closed triangle (black arrows) on the labial side and the third mandibular molar (m3) has 4 closed triangles, one of which is much smaller (labial side; Naughton, 2012). -
Lower molars of Mictomys borealis. The third lower molar (m3) has 3 closed loops, not 4. The mandibular molars lack closed triangles on the lingual side (Naughton, 2012). -
In Synaptomys cooperi, the posterior edge of the palate ends with a broad blunt median projection or what looks like two poorly developed processes. -
In Mictomys borealis, the posterior edge of the palate has a well developed spinous process (Naughton, 2012). -
Lower incisors of Synaptomys cooperi. Linzey (1983) noted that the mandibular incisors are "heavy". -
Lower incisors of Mictomys borealis. Howell (1927) noted that "the lower incisors are very long, slender, and exceedingly sharply pointed."
References
Hazard EB. 1982. The mammals of Minnesota. Minneapolis (MN, USA): University of Minnesota Press.
Howell AB. 1927. Revision of the American lemming mice (genus Synaptomys) (No. 50). US Government Printing Office.
Hope AG, Headlee KM, Olson ZH, Wiens BJ. 2023. Systematics, biogeography and phylogenomics of northern bog lemmings (Cricetidae), cold-temperate rodents of conservation concern under global change. Systematics and Biodiversity 21:1:2237050. https://doi.org/10.1080/14772000.2023.2237050
Naughton D. 2012. The natural history of Canadian mammals. Toronto (ON, CA): University of Toronto Press.
Richardson J. 1828-04. Short characters of a few quadrupeds procured on Capt. Franklin's late expedition. Zoological Journal 3(12):516-520.