Mictomys borealis
Hope et al. (2023) provided "multiple lines of evidence that define systematic relationships, and support firm recognition of northern bog lemmings as Mictomys borealis, distinct at the generic level from Synaptomys."
Northern Bog Lemming
(Mictomys borealis) | |
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Range | |
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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) |
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 |
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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
From Howell (1927): "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 the subgenus Synaptomys in the absence of an outer triangle from each tooth, and in having the buccal borders crenulate, with outer reentrant angles barely indicated, except in the third molar, where one is slightly developed. 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 the subgenus Synaptomys. The lower incisors are very long, slender, and exceedingly sharply pointed."

Similar species
Differences between Synaptomys cooperi and Mictomys borealis (formerly S. borealis) are given in the key below, which is based on Linzey (1983) and Naughton (2012). The new name for Synamptomys borealis is Mictomys borealis, based on Hope et al. (2023).
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
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.