Comments on
the Taxonomy and Geographic Distribution
of North American Microtines

BY

E. RAYMOND HALL AND E. LENDELL COCKRUM

University of Kansas Publications
Museum of Natural History
Volume 5, No. 23, pp. 293-312
November 17, 1952

University of Kansas
LAWRENCE
1952

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. 23, pp. 293-312
November 17, 1952

University of Kansas
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS 1952

Comments on
the Taxonomy and Geographic Distribution
of North American Microtines

BY

E. RAYMOND HALL and E. LENDELL COCKRUM

In preparing maps showing the geographic distribution of North American microtines, conflicting statements in the literature and identifications that, if accepted, would result in improbable geographic ranges have led to the examination of pertinent specimens with the results given below. The studies here reported upon were aided by a contract between the Office of Naval Research, Department of the Navy, and the University of Kansas (Nr 161-791), by funds provided by the University of Kansas from its Research Appropriation, and by grants for out-of-state field work from the Kansas University Endowment Association. Grateful acknowledgment is made to persons in charge of the collections at each of the following institutions for permission to use the collections under their charge: Biological Surveys Collection, United States National Museum (herein abbreviated USBS); California Museum of Vertebrate Zoology (MVZ); Chicago Natural History Museum (CNHM); University of Kansas Museum of Natural History (KU); Museum of Comparative Zoology (MCZ); United States National Museum (USNM); Department of Economic Zoology, University of Wisconsin (UWDEZ); and Zoological Museum, University of Wisconsin (UWZM).

When Bole and Moulthrop named Synaptomys cooperi saturatus, with type locality in Illinois, they, in effect, divided the geographic range of Synaptomys cooperi stonei into two parts (see A. B. Howell, N. Amer. Fauna, 50:10 (fig. 2), August 5, 1927) since Bole and Moulthrop (op. cit.) did not assign to any subspecies the specimens from southern Wisconsin that Howell (op. cit.) had identified as S. c. stonei. Bole and Moulthrop's inclusion in their newly named subspecies of a specimen from as far west as East Columbia, Missouri, left in doubt the subspecific identity of specimens from Iowa and a specimen from Arkansas. Howell (op. cit.) had assigned this material from Iowa and Arkansas to S. c. gossii.

Howell recognized that the one individual (168266 USBS) from Lake City, Arkansas, was too young to be identified to subspecies with certainty and assigned the specimen to S. c. gossii "upon geographical grounds" (op. cit.:19). Keith R. Kelson and one of us (Hall) compared this specimen with pertinent materials. As a result of this comparison we refer the specimen, on the same grounds employed by Howell, to Synaptomys cooperi saturatus.

Specimens from approximately the southern half of Wisconsin (from Kelly Lake southward) were referred to S. c. stonei by Howell (op. cit.:16). Now that S. c. saturatus has been recognized, these specimens from southern Wisconsin would be expected to be referable to S. c. saturatus. When these specimens were examined and compared (by Hall and Kelson) with other specimens in the United States National Museum the skulls were found to be much larger than in S. c. cooperi, smaller than in S. c. gossii, and nearly the size of those of Synaptomys cooperi saturatus, to which subspecies we refer the specimens in question.

Howell (op. cit.:16) referred a specimen from Cassopolis, Michigan, a locality that might be presumed to fall within the range of the more recently named S. c. saturatus, to S. c. stonei. Bole and Moulthrop did not mention this specimen when they described and named S. c. saturatus (1942). Neither did Burt, but Cassopolis is within the geographic range ascribed to S. c. cooperi on his map (The Mammals of Michigan, Univ. Michigan Press, p. 213, 1946). Examination (by Kelson and Hall) of the specimen (41777 MCZ) reveals that it resembles S. c. cooperi in shortness of hind foot (18 mm.), shortness of tail (18 mm.), narrowness across zygomata (16 mm.), and grayish pelage. In the long braincase, heavy rostrum, greater condylobasilar length, greater lambdoidal breadth, long rostrum, and longer incisive foramina, it agrees closely with specimens of S. c. saturatus, to which subspecies we refer the specimen.

Necker and Hatfield (Bull. Chicago Acad. Sci., 6:54, 1941) referred specimens from Rosiclaire, Illinois, to S. c. gossii. These specimens were not mentioned by Bole and Moulthrop (op. cit.) when they named S. c. saturatus although the specimens presumably would be referred to the newly-named subspecies. We have examined the pertinent specimens (Nos. 15781-15786 and 16049-16054 CNHM) and find that on the basis of dark color, long and slender skull, heavy incisors, and small cheek-teeth, they are referable to S. c. saturatus Bole and Moulthrop. None, however, has a tail so short as the type of S. c. saturatus. For that matter, the average length of the tail of six near topotypes (5 mi. W, 2½ mi. S Monticello, Piatt County, Illinois, Nos. 32037-32042 KU) exceeds that of the type (17.4 mm., range 12-20, as compared to 14 mm. for the type).

In view of the taxonomic treatment accorded by Bole and Moulthrop (Sci. Publs. Cleveland Mus. Nat. Hist, 5:149-151, September 11, 1942) to the lemming mice of the species Synaptomys cooperi, as explained in the preceding account, it has seemed desirable to examine Iowan specimens of this species. Hall and Kelson examined the necessary material and made the following conclusions. An adult male from Hillsboro (168453 USBS) has the lighter color and large skull of S. c. gossii to which Howell (N. Amer. Fauna, 50:19, August 5, 1927) referred the specimen. The more western specimen from Knoxville, a young male (190358 USNM), is almost exactly the same age as a male of S. c. saturatus from Bascom, Indiana (143701 USNM), and is but slightly older than a male S. c. gossii from Ft. Leavenworth, Kansas (91583 USBS). The upper molariform tooth-row is the same length in the specimens from Kansas and Iowa, but is longer in that from Indiana. The fact that the specimen from Knoxville closely resembles the Kansan specimen in other dimensions of the skull, which is larger than in the specimen