A New Subspecies of Microtus montanus fromMontana and Comments on Microtuscanicaudus Miller

BY

E. RAYMOND HALL and KEITH R. KELSON

University of Kansas PublicationsMuseum of Natural HistoryVolume 5, No. 7, pp. 73-79October 1, 1951

University of KansasLAWRENCE1951

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Edward H. Taylor, Robert W. Wilson

Volume 5, No. 7, pp. 73-79October 1, 1951

UNIVERSITY OF KANSASLawrence, Kansas

PRINTED BYFERD VOILAND, JR. , STATE PRINTERTOPEKA, KANSAS1951

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A New Subspecies of Microtus montanus from Montana and Comments onMicrotus canicaudus Miller

BY

E. RAYMOND HALL AND KEITH R. KELSON

In 1949, for the Museum of Natural History of the University of Kansas, Mr. John A. White collected two specimens of the species _Microtusmontanus_ in the Bitterroot Valley of Montana, that did not fit thedescription of any named subspecies. These were laid aside until wecould examine the additional specimens from Montana in the BiologicalSurveys collection in the United States National Museum, some of whichpreviously had been reported by Bailey (N. Amer. Fauna, 17:31, June 6, 1900) under the name _Microtus nanus canescens_ Bailey [=_Microtusmontanus canescens_]. Our examination reveals that the animals from theBitterroot and Flathead valleys belong to an heretofore unrecognizedsubspecies which is named and described below. 

 Microtus montanus pratincolus new subspecies

 _Type. _--Female, adult, skull and skin, No. 34004, Univ. Kansas, Mus. Nat. Hist. ; from 6 mi. E Hamilton, 3700 ft. , Ravalli County, Montana; obtained on August 14, 1949, by John A. White; original number 477. 

 _Geographic distribution. _--Flathead and Bitterroot valleys of western Montana. 

 _Diagnosis. _--Size small for the species (see measurements). Color: Essentially as in _Microtus montanus nanus_. Skull: Small, slender, and comparatively smooth; rostrum moderately depressed distally; nasals moderately inflated distally and extending posteriorly not quite to tips of premaxillary tongues; nasals usually truncate posteriorly, but rounded in some individuals; premaxillary tongues terminating posteriorly in a short medial spine; zygomatic arches lightly constructed and usually more widely spreading posteriorly than anteriorly; interparietal comparatively long and terminating in a small, but distinct, medial spine, otherwise approximately rectangular in shape; exposed parts of upper incisors short and, for the species, only slightly procumbent; molar dentition weak and, in most specimens, especially so posteriorly; tympanic bullae large and well inflated, especially ventrolaterally; basioccipital narrow owing to the encroachment of the tympanic bullae. 

 _Comparison. _--Among named forms, _Microtus montanus pratincolus_ most closely resembles _Microtus montanus nanus_. The geographic range of _M. M. Nanus_ adjoins that of _M. M. Pratincolus_ on three sides; there is no conspecific subspecies adjoining the range of _M. M. Pratincolus_ on the north. From _M. M. Nanus_, _M. M. Pratincolus_ differs as follows (measurements are all of males, those of _M. M. Nanus_ being of nine topotypes and near topotypes from central Idaho): size smaller (149 mm. As opposed to 165), tail shorter (37 as opposed to 39), hind foot shorter (19 as opposed to 20), upper molar series shorter (expressed as a percentage of basilar length, 25. 5 as opposed to 26. 3), mastoidal region broader (expressed as a percentage of basilar length, 48. 6 as opposed to 46. 7), braincase slightly more vaulted (depth of braincase expressed as a percentage of basilar length, 31. 3 as opposed to 30. 4) and more inflated laterally; tympanic bullae more inflated, this inflation being the most conspicuous difference between the two subspecies. The tympanic bullae of _M. M. Pratincolus_ have approximately a fourth more volume than those of _M. M. Nanus_. 

_Remarks. _--Northwardly in the Bitterroot Valley, specimens of _M. M. Pratincolus_ morphologically approach _M. M. Nanus_, especially in thereduced degree of inflation of the tympanic portion of the bullae. Ongeographic grounds we think that the geographic range of _M. M. Pratincolus_ extends southward to the southern end of the BitterrootValley; we have not seen specimens from that area. Although we have notexamined the specimen reported upon by Davis (Murrelet, 18:26, September4, 1937) from Canyon Creek, "a few miles west of Hamilton", Montana, wethink that it will be found to belong to _M. M. Pratincolus_. 

Our examination of specimens from localities in Montana east of therange here ascribed to _M. M. Pratincolus_ indicates that, among namedkinds of _Microtus_, those specimens are best referred to _M. M. Nanus_. These specimens are listed below under comparative materials. It shouldbe mentioned here that although Bailey (_loc. Cit. _) applied the name_Microtus nanus canescens_ to Montanan specimens from Flathead Lake andHot Springs Creek, the subspecies _M. Montanus canescens_ now is thoughtto be restricted to Washington and the adjoining part of BritishColumbia; _M. M. Canescens_ does not occur so far east as Montana. 

Grateful acknowledgment is made to those persons in charge of theBiological Surveys collection for permission to study the specimens inthat collection, and to the Kansas Endowment Association for support ofthe field work which yielded the specimens from six miles east ofHamilton, Montana. The study here reported upon was aided also by acontract between the Office of Naval Research, Department of the Navy, and the University of Kansas (NR 161-791). 

 _Measurements. _--The following measurements in millimeters are those of the holotype and the average, maximum, and minimum, respectively, of eleven adult males from various places in the range of the subspecies. Except as noted below, we are unable to detect significant morphological differences in the populations sampled and believe that pooling of the measurements is justifiable in this case. Measurements are: Total length, 129, 149 (156-141); length of tail-vertebrae, 27, 37 (39-31); length of hind foot, 18, 19 (20-18) (all preceding measurements are those of the collectors); basilar length, 22. 2, 24. 5 (25. 7-23. 4); greatest length of nasals, 6. 7, 6. 9 (7. 4-6. 4); zygomatic breadth, 14. 2, 14. 6 (14. 9-13. 9); mastoidal breadth, 11. 3, 11. 8 (12. 3-10. 8); alveolar length of upper molar series, 6. 0, 6. 2 (6. 5-5. 9); depth of braincase (shortest distance from ventral surface of basioccipito-basisphenoidal suture to the dorsal surface of the cranium, and not perpendicular to the long axis of the skull), 7. 7, 7. 7 (7. 9-7. 5); width of rostrum, 4. 7, 4. 8 (5. 0-4. 6); interorbital breadth, 3. 2, 3. 4 (3. 6-3. 2). Measurements of females, other than those of the holotype, are not given owing to the lack of sufficient material. Females, however, do not appear to differ appreciably in measurements from males. 

 _Specimens examined_ (in U. S. Nat. Mus. , Biol. Surv. Coll. , except as otherwise indicated). --Total, 26, all from Montana, as follows: _Sanders Co. _: Hot-springs Cr. , 4. _Lake Co. _: end of W arm Flathead Lake, 5; Ravalli, 8. _Ravalli Co. _: Florence, 2; 8 mi. NE Stevensville, 4000 ft. , 1; Corvallis, 4; 6 mi. E Hamilton, 3700 ft. , 2(K. U. ). 

 _Comparative materials_ (in U. S. Nat. Mus. , Biol. Surv. Coll. ). --_Microtus montanus nanus_: Total, 72, as follows: IDAHO: _Lewis Co. _: Nez Perce, 3. _Idaho Co. _: Seven Devils Mts. , 3550 ft. , 3. _Custer Co. _: Challis, 7; Pahsimeroi Mts. (9300 ft. , 8; 9700 ft. , 4), 12. _Butte Co. _: Lost River Mts. , 1. _Canyon Co. _: Nampa, 1; Bowmont, 1. _Ada Co. _: Boise, 1. _Blaine Co. _: Sawtooth Lake, 2; Alturas Lake, 3. _Owyhee Co. _: Three Cr. , 3. _Minidoka Co. _: Heyburn, 2. _Bannock Co. _: Pocatello, 4. _Bear Lake Co. _: Montpelier Cr. , 3. MONTANA: _Fergus Co. _: Big Snowy Mts. , 11. _Gallatin Co. _: West Fork of West Fork, Gallatin River, 1. _Park Co. _: Lamar River, 7000 ft. , 2; Gardiner, 1. _Sweetgrass Co. _: "near" head Big Timber Cr. , Crazy Mts. , 1; Big Timber Cr. , 5200 ft. , Crazy Mts. , 1; 14 mi. S Big Timber, 1; West Boulder Cr. , 18 mi. SE Livingston, 2; McLeod, 1. _Carbon Co. _: Beartooth Mts. , 2; Beartooth Lake, 1. WYOMING: _Park Co. _: N end Lake, Yellowstone Nat'l Park, 2. 

 Microtus montanus canicaudus Miller

 1897. _Microtus canicaudus_ Miller, Proc. Biol. Soc. Washington, 11:67, April 21, type from McCoy, Willamette Valley, Polk County, Oregon. 

In 1938 when one of us (Hall, Proc. Biol. Soc. Washington, 51:131-134, August 23, 1938) arranged several nominal species of _Microtus_ assubspecies of the species _Microtus montanus_, _Microtus canicaudus_ wasnot included because that writer had not examined representativespecimens. In the U. S. Biological Surveys collection in the U. S. National Museum we have examined specimens of _M. M. Canicaudus_, allfrom Oregon, as follows: Hood River (Catalogue Nos. 262583-262586);Canby (262577, 262578); Wapinitia (79985-79988); Sheridan (69779, 69780); McCoy (75834-75842, 77744); Salem (246736); Albany (161554); andCorvallis (242552). The four specimens from Wapinitia seem to be thosethat Bailey (N. Amer. Fauna, 17:29, June 6, 1900) listed as _Microtusmontanus_. The diagnostic characters mentioned by Miller in theoriginal description (Proc. Biol. Soc. Washington, 11:67, April 21, 1897) included the following: size approximately the same as in_Microtus [montanus] nanus_; upper parts yellowish; tail usually nearlyuniform grayish above and below; auditory bullae much inflated; lateralpits at posterior edge of bony palate unusually shallow. Because thetails of the original series were understuffed and variously rotated, they seemed to be less sharply bicolored than is the case, as shown bysubsequently collected specimens. Otherwise we find that the charactersmentioned above differentiate _canicaudus_ from its nearest relatives, _Microtus montanus canescens_ to the northward, _M. M. Nanus_ to theeastward, and _M. M. Montanus_ to the southward. In _canicaudus_ we havenoted one additional differential character; the interpterygoid space isacuminate anteriorly. In this feature and in each of the other featuresmentioned above, intergradation with _Microtus montanus nanus_ is seenin the specimens from Hood River and Wapinitia. In the specimens fromHood River the auditory bullae are only slightly less inflated than inthose topotypes of _canicaudus_ having the smallest bullae; there isappreciable variation in size of the bullae in the topotypes. Even so, the minimum size of bullae among the topotypes is larger than themaximum size in the specimens from Wapinitia. The four specimens fromWapinitia have the yellowish color of _canicaudus_ to a considerabledegree, and show intergradation between _canicaudus_ and _nanus_ indepth of the palatal pits and shape of interpterygoid space. Theslightly larger size of these specimens from Wapinitia suggestsintergradation with _M. M. Montanus_. The tympanic bullae in thespecimens from Wapinitia seem to be smaller than in specimens of_canicaudus_, _nanus_, or _montanus_. 

Because of the intergradation described above between _Microtus montanusnanus_ and _M. Canicaudus_, the latter should stand as _Microtusmontanus canicaudus_. 

 * * * * *

Bailey (N. Amer. Fauna, 55:206, August 29, 1936) recorded _canicaudus_from Warm Springs in the Deschutes Valley of Oregon and from the stateof Washington. Other authors also have recorded _canicaudus_ from thestate of Washington. Our examination of specimens leads us to conclude, as did Dalquest (Univ. Kansas Publ. , Mus. Nat. Hist. , 2:348, 349, April9, 1948), that _canicaudus_ does not occur in Washington. The reportedoccurrence of _M. Canicaudus_ at Warm Springs, Deschutes Valley, Oregon, seems to be the result of an error in identification. The specimensconcerned seem to be two _Microtus longicaudus mordax_ (Nos. 207060 and207082 U. S. N. M. ). They are labeled as collected at "Warm Springs (MillCr. --20 Mi. W of)". Bailey's (_op. Cit. _, fig. 46, p. 209) map showingthe distribution in Oregon of _Microtus mordax mordax_ [=_Microtuslongicaudus mordax_] has a locality-dot at Warm Springs itself. Baileyseems to have erred; he should have placed this dot 20 miles fartherwest, we think. When preparing his map (_op. Cit. _, fig. 43, p. 205)showing the geographic distribution of _Microtus canicaudus_, Baileyseems to have misidentified these same two specimens as _M. Canicaudus_, and for them placed a locality-dot on his map 20 miles east (instead ofwest) of Warm Springs. In brief, Bailey probably did not see anyspecimens of _canicaudus_ or specimens of any other subspecies of_Microtus montanus_ from Warm Springs. 

_Transmitted February 15, 1951. _

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