Comments On The Taxonomy And Geographic Distribution Of North American Part 1

Comments on the Taxonomy and Geographic Distribution of North American Microtines.

by E. Raymond Hall and E. Lendell c.o.c.krum.

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 a.s.sociation. Grateful acknowledgment is made to persons in charge of the collections at each of the following inst.i.tutions 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).

Synaptomys cooperi saturatus Bole and Moulthrop

1942. _Synaptomys cooperi saturatus_ Bole and Moulthrop, Sci.

Publs. Cleveland Mus. Nat. Hist., 5:149, September 11, type from Bloomington, McLean County, Illinois.

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 a.s.sign 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 ident.i.ty of specimens from Iowa and a specimen from Arkansas. Howell (_op. cit._) had a.s.signed 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 a.s.signed 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 Ca.s.sopolis, 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 Ca.s.sopolis 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, 2-1/2 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).

Synaptomys cooperi gossii (Coues)

1877. _Arvicola (Synaptomys) gossii_ Coues, Monogr. N. Amer.

Rodentia, p. 235 (published as a synonym of _Synaptomys cooperi_, but name stated to apply to Kansan specimens of which description and measurements are on p. 236), type from Neosho Falls, Woodson County, Kansas.

1897. _Synaptomys cooperi gossii_, Rhoads, Proc. Acad. Nat. Sci.

Philadelphia, 49:307, June.

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 from Indiana, gives a basis for applying the name _Synaptomys cooperi gossii_ to the specimen from Knoxville. This is the same name recently used by Fichter and Hansen (Bull. Univ. Nebraska State Mus., 3(2):2, September, 1947) for the Iowan specimens, although they seemingly applied the name without being aware of Bole and Moulthrop's earlier naming of _S. c. saturatus_ (Sci. Publs. Cleveland Mus. Nat. Hist., 5:149, September 11, 1942).

Synaptomys borealis sphagnicola Preble

1899. _Synaptomys (Mictomys) sphagnicola_ Preble, Proc. Biol. Soc.

Was.h.i.+ngton, 13:43, May 29, type from Fabyans, Coos County, New Hamps.h.i.+re.

1927. _Synaptomys borealis sphagnicola_, A. B. Howell, N. Amer.

Fauna, 50:30, August 5.

Howell (N. Amer. Fauna, 50:30-31, August 5, 1927) had only eight specimens of this subspecies available when he revised the genus _Synaptomys_. Of these eight (Maine: Mount Katahdin, 2; New Brunswick: Near Bathurst, 1; New Hamps.h.i.+re: Fabyans, 1, the type; Quebec: St.

Rose, 4), only the type and one of the specimens from St. Rose are adults. Concerning the others, Howell wrote (_op. cit._:31): "The example from near Bathurst is not adult and has a damaged skull, so is identified provisionally. All other specimens are too young for positive diagnosis."

Since Howell's revision only one additional specimen has been reported.

Anderson (Ann. Rept. Provancher Soc. for 1939, p. 71, 1940) reported it from Table Mountain, 3888 ft., Gaspe County, Quebec.

In the collection of the University of Kansas Museum of Natural History there is still another specimen. It is an adult male topotype (No. 6483 KU, formerly No. 72 in the collection of Alfred E. Preble) obtained on August 21, 1905, at Fabyans, New Hamps.h.i.+re. The measurements of this specimen are as follows (measurements in parenthesis are those of the type as given by Howell, _op. cit._): Total length, 135 (132); tail, 26 (24); hind foot, 22 (20); condylobasilar length, 25.1 (25.8); rostral length, 6.5 (6.8); rostral breadth, 4.7 (4.9); interorbital breadth, 3.3 (2.8); zygomatic breadth, 15.4 (16.0); lambdoidal breadth, 12.1 (12.4); incisive foramina, 5.9 (5.7); height of skull, 9.1 (9.3).

Howell (_op. cit._:30) characterized _S. b. sphagnicola_ as: "Large and high [skull] with narrow interorbital sharply ridged, the ridges of the type being joined for a distance of 4 millimeters; interparietal narrow and rectangular. The rostrum is long, tapering very little, and the nasals, slightly constricted medially are quite narrow posteriorly. The incisive foramina are long and wide." Howell further stated (_op.

cit._:30-31) that: "It is hard to predict what will be found to const.i.tute the most valuable cranial characters in distinguis.h.i.+ng this race from adult _medioximus_. The discernible differences now are in the shape of the interparietals, rostral characters, and interorbital differences that will probably not hold good when animals of the same age are compared."

As can be seen from a comparison of the measurements given above for the type and the topotype, some of the characteristics given by Howell are not found in the topotype: The interorbital region is not narrow (in fact it is wider than it ordinarily is in some other subspecies of _Synaptomys borealis_) and the incisive foramina are not longer than in other subspecies of _Synaptomys borealis_.

As far as present material permits us to judge, _Synaptomys borealis sphagnicola_ is characterized, cranially, by: Skull large; interorbital region sharply ridged (the ridges being joined for a distance of 4 mm.

in the type and of 4.5 mm. in the topotype); rostrum long, tapering relatively little; nasals slightly constricted medially and unusually narrow posteriorly; interparietal narrow and rectangular.

Clethrionomys occidentalis caurinus (Bailey)

1898. _Evotomys caurinus_ Bailey, Proc. Biol. Soc. Was.h.i.+ngton, 12:21, January 27, type from Lund, east sh.o.r.e Malaspina Inlet, British Columbia.

1935. _Clethrionomys gapperi caurinus_, Racey and Cowan, Rept.

British Columbia Prov. Mus. for 1935, p. H 25.

Prior to 1935 _caurinus_ was considered to be a monotypic species. In 1935 Racey and Cowan (Rept. British Columbia Provincial Museum for 1935, pp. H 25-H 26) examined material from southwestern British Columbia of _C. caurinus_, including a series of 24 specimens from Alta Lake, and compared it with _Clethrionomys gapperi occidentalis_ and _C. g. saturatus_. They found _caurinus_ to be distinct from _C. g.

saturatus_ but were "not convinced that _occidentalis_ and _caurinus_ both merit systematic recognition; should they prove to be indistinguishable, as the little available material indicates, _occidentalis_ will take precedence on grounds of priority. It is our opinion that further study of the distribution of the genus in British Columbia will lead to the recognition of _occidentalis_ as the form inhabiting coast-line and _saturatus_ the interior of British Columbia"

p. H 26. In the face of these opinions Racey and Cowan nevertheless recognized _caurinus_ under the name _Clethrionomys gapperi caurinus_ (Bailey).

In spite of the treatment by Racey and Cowan (_op. cit._) of _occidentalis_ and _caurinus_ as subspecies of _C. gapperi_, later authors arranged _occidentalis_ as a member of the "_californicus_"

group although they retained _caurinus_ in the _gapperi_ group. For example, Davis (The Recent Mammals of Idaho, The Caxton Printers, pp.

307-308, 1939) a.s.signed _C. caurinus_ to the _gapperi_ group, although he regarded _C. caurinus_ as a species (not a subspecies). He regarded also _C. occidentalis_ as a species (not a subspecies) but a.s.signed it to the _californicus_ group. Dalquest (Univ. Kansas Publ., Mus.

Nat. Hist., 2:344, April 9, 1948) considered _occidentalis_ to be conspecific with _Clethrionomys californicus_ and wrote (_op.

cit._:101): "The _californicus_ group, I feel, contains only the races of _Clethrionomys californicus_, while the _gapperi_ group contains _C.

gapperi_ and its races, including _caurinus_, and possible other species." Dalquest gave no indication that he had examined any specimens of _caurinus_.

When Dalquest (_op. cit._:344) arranged _occidentalis_ and _californicus_ as subspecies of the same species, he used the name combination _Clethrionomys californicus occidentalis_ because he ignored, or was unaware of, the page priority of _occidentalis_ over _californicus_. We regard the anterior position of _occidentalis_ as nomenclatural priority and therefore employ _occidentalis_ rather than _californicus_ as the specific name.

Differences between the _gapperi_ group and the _occidentalis_ group include: postpalatal bridge (complete in both groups) truncate posteriorly in the _gapperi_ group and with a median, posteriorly directed, spine in the _occidentalis_ group (this character is not evident in all specimens; some _gapperi_ have a spine, and some _occidentalis_ have the spine much reduced); dent.i.tion of the _occidentalis_ group is heavier; enamel pattern of M3 and m1 in _occidentalis_ more simplified--the number of salient and re-entrant angles tends to be reduced in adults of the _occidentalis_ group.

An examination of specimens of _caurinus_ (British Columbia: Mt.

Seymour, 2 KU; Lund, Malaspina Inlet, 2 USBS; and Inverness, mouth Skeena River, 1 USBS), reveals that, in the presence of the median postpalatal spine and in the characters of the molars, _caurinus_ agrees with the _occidentalis_ group.

Clethrionomys occidentalis nivarius (Bailey)

1897. _Evotomys nivarius_ Bailey, Proc. Biol. Soc. Was.h.i.+ngton, 11:136, May 13, type from northwest slope of Mount Ellinor, 4000 ft., Olympic Mts., Mason County, Was.h.i.+ngton.