Fig. 41
Baculum: Stalk broad, greatest length (3.0 mm.) 1½ times greatest breadth, 4½ times greatest depth; three ossified processes, median one largest, deeper and more than twice as wide as curved, shorter, compressed lateral processes and more than2/5as long as stalk; base broad, in dorsal view posterior profile trilobate, basal tuberosities visible; basal tuberosities well developed, medially confluent; in end-view base wider ventrally than dorsally, dorsal concavity deeper than ventral concavity; medial constriction3/5of greatest depth; shaft broad, at mid-point more than twice as wide as high and1/3as wide as base of stalk, terminally rounded.
Specimens examined: Three, allM. t. townsendii; Fort Lewis, Pierce Co., Washington, 57998, subadult; Sec. 33, T. 11S, R. 5W, Benton Co., Oregon, 79186; Sec. 5, T. 12S, R. 4W, Benton Co., Oregon, 79188.
Fig. 44
Baculum: Stalk broad and flattened, greatest length (3.5 mm.) 12/3to 2 times greatest width, 4 to 5½ times greatest depth; three ossified processes, median one largest, lateral processes slender, relatively small; length of median process3/8length of stalk; median process decurved, dorsoventrally flattened insome specimens, widened at base; attachment of processes to shaft displaced ventrally; base of stalk widened, posterior profile in dorsal view usually trilobate, in a few cases rounded, median lobe forming posterior shelf, lateral lobes dorsally raised and forming margins of lateral tuberosities; in end-view thickness frequently more or less uniform throughout central part, broad depression dorsally, ventral concavity narrower and shallower (as figured); base, and occasionally shaft, flattened, width at mid-point of stalk 2 to 3 times depth, narrowest point posterior to terminal inflation of shaft in terminal1/3of shaft.
The baculum ofM. oeconomus(Old World) figured by Ognev (1950:257) resembles but exceeds that ofM. oeconomus(New World) in the relatively large median process and slender lateral processes, but differs noticeably in the presence of a deep median notch in the base of the stalk. A specimen from Hungary is intermediate between Ognev's specimen and those from the New World in both size of median process and size of lateral processes, and has an unnotched base resembling that in Figure 44.
Specimens examined: Ten, of three subspecies;M. oeconomus gilmorei, Umiat, Alaska, 51354, 51361, 51399, 51408; Lake Schrader, Brooks Range, Alaska, 51422;M. o. macfarlani, 5 mi. NNE Gulkana, Alaska, 43039, 43041; 20 mi. NE Anchorage, Alaska, 43044; Kelsall Lake, British Columbia, 43048;M. o. mehelyi, Kisbalatan, Hungary, 75159.
Figs. 35 and 36
Baculum: Stalk attenuate, greatest breadth relatively near proximal end; greatest length (3.1 to 3.4 mm.) more or less twice greatest breadth, 4 to 5 times greatest depth; usually a single process ossified; lateral processes relatively small, cartilaginous or (in three specimens, 63094, 69453, 68019) with small ossifications; median process relatively small, sometimes appressed to tip of shaft, in length less than ¼ length of stalk; posterior profile in dorsal view rounded, flattened posteriorly, or in some specimens trilobate with angular edges; in end-view relative depths of dorsal and ventral concavities variable, dorsal usually deeper than ventral; distal end of stalk frequently bowed dorsally; shaft slender distally, sometimes slightly inflated terminally, or (in one specimen, 63085) near tip small lateral projections that are perhaps fused lateral ossifications; lateral profile in dorsal view a gradual slope anteriorly from point of greatest width to slender tip.
Specimens examined: Thirteen, of four subspecies;Microtus mexicanus mexicanus, Las Vigas, Veracruz, 30692; Nevada de Toluca, México, 63101; Valle de Bravo, México, 63094;Microtus mexicanus mogollonensis, Mt. Taylor, Valencia Co., New Mexico, 63298, 76830; Park Well, Mesa Verde National Park, Montezuma Co., Colorado, 69448, 69453; Upper Nutria, McKinley Co., New Mexico, 69997, 70000;Microtus mexicanus phaeus, Sierra Patamba, 9000 ft., Michoacán, 63085;Microtus mexicanus subsimus, 2 mi. E Mesa de Tablas, Coahuila, 58916; 13 mi. E San Antonio de las Alazanas, Coahuila, 68019, 68021.
Fig. 37
Baculum: Stalk elongate, greatest length (3.0 mm.) 21/3times greatest breadth, 4½ times greatest depth; median process ossified, ¼ length of stalk, basally broadened, flattened and shallowly grooved ventrally to fit tip of shaft, to which the process is closely appressed; lateral processes cartilaginous; endsof stalk bowed upwardly; posterior profile of base of stalk rounded or slightly trilobate if posterolateral concavities form in tuberosities; moderate development of tuberosities, in end-view dorsal concavity slightly deeper and narrower than ventral concavity, both comparatively shallow, median constriction4/5greatest depth; shaft curved, more or less terete at mid-point of stalk, terminally inflated dorsally; lateral profile in dorsal view gradually curved from point of greatest width anteriorly onto shaft.
Specimens examined: Two, of two subspecies;Microtus californicus californicus, 1 mi. NE Berkeley, in Contra Costa Co., California, 76828;Microtus californicus mohavensis, ½ mi. SE Victorville, San Bernardino Co., California, 63745.
Figs. 14, 15, 16 and 17
Baculum: Stalk heavy, broad, greatest length (2.2 to 3.0 mm.) 11/3to 12/3times greatest breadth, up to 3¾ times greatest depth; three ossified processes, median one largest, usually not twice so deep as lateral ossifications; median process usually distinctly widened basally, in length approximately ½ length of stalk; base broad, frequently angular laterally and basally, sometimes bilobate; basal tuberosities well developed, medially confluent; in end-view more or less uniformly biconvex or ventral surface more flattened than dorsal surface, medial constriction ½ to2/3greatest depth; shaft relatively heavy, at mid-point stalk almost twice as wide as deep and1/3as wide as base of stalk; shaft terminally rounded and sometimes slightly inflated; lateral profile in dorsal view abruptly or gradually curved anterior to point of greatest width and then gradually curved anteriorly.
Specimens examined averaged slightly smaller and were more variable than those described by Hamilton (1946:382). The greater variation may be in part geographic, as five subspecies are represented. Lateral processes are the last to ossify. One specimen (75082) with well-ossified median process lacks any lateral ossification. Four bacula ofM. pennsylvanicus(locality not specified) studied by Dearden (1958:547) agree in general with the description above.
One specimen shows a break, perhaps resulting from injury, in the shaft (Fig. 14). One specimen has a posteromedian spine on the median digital ossification (Fig. 16). Comparison withM. agrestisis included with the description ofM. agrestis.
Specimens examined: Thirteen, of six subspecies;Microtus pennsylvanicus alcorni, 20 mi. NE Anchorage, Alaska, 43043;Microtus pennsylvanicus finitus, Laird, Yuma Co., Colorado, 68544;Microtus pennsylvanicus modestus, 5 mi. N, 26 mi. W Saguache, 9500 ft., Saguache Co., Colorado, 42306; 3 mi. N, 16 mi. W Saguache, 8500 ft., Saguache Co., Colorado, 42416, 42417, 42418; 1 mi. S, 2 mi. E Eagle Nest, 8100 ft., Colfax Co., New Mexico, 42430, 42439;Microtus pennsylvanicus pennsylvanicus, 2 mi. S, 3 mi. E Ft. Thompson, 1370 ft., Buffalo Co., South Dakota, 42379; Vermillion, Clay Co., South Dakota, 37070;Microtus pennsylvanicus pullatus, 12 mi. S, 5 mi. E Butte, Silver Bow Co., Montana, 57501, 57503;Microtus pennsylvanicus uligocola, Muir Springs, 2 mi. N, 2½mi. W Ft. Morgan, Morgan Co., Colorado, 75082.
Fig. 18
Baculum: Greatest length of stalk (2.9 mm.) twice greatest breadth, 4½ times greatest depth; stalk well developed, shaft not flattened dorsoventrally; large median ossified process, minute lateral ossifications in single specimenexamined; length of stalk 2½ times length of median ossification which is higher than wide, slightly decurved, sagittate in dorsal view, with three-cornered base; basal tuberosities of stalk moderately well developed, medially joined; posterior profile in dorsal view evenly rounded; ventral concavity broader than, but of comparable depth to, dorsal concavity in end-view, base of stalk wider ventrally, constriction ¾ greatest depth; at mid-point of stalk shaft is but slightly wider than high; pronounced terminal inflation of shaft; lateral profile in dorsal view sloping abruptly from widest point of stalk anteriorly onto stalk which then tapers more gradually to terminal inflation.
From the baculum of its New World counterpart, namelyMicrotus pennsylvanicus, my specimen ofMicrotus agrestisand the specimen figured by Didier (1954:239) differ in their minute lateral processes, relatively larger median processes, and more elongate, less dorsoventrally flattened shafts.
The specimen ofM. agrestisfigured by Ognev (1950:320), in dorsal view has lateral concavities producing a somewhat trilobate outline in the base of the stalk, and the lateral processes are well developed; the median process is larger and bulbous, wider distally than proximally. Without larger numbers of bacula ofM. agrestisI am unable to reconcile these differences. The differences betweenM. agrestisandM. pennsylvanicusseem comparable to the differences between some other species ofMicrotus.
Specimen examined: One, from Gryon, Switzerland, 67102.
Fig. 31
Baculum: Stalk broad, greatest length (3.2-4.0 mm.) 12/3to 2 times greatest breadth, 2½ to 4 times greatest depth; median process ossified, relatively small, less than3/10length of stalk; lateral processes arising from subterminal part of stalk, cartilaginous or with small ossifications; posterior profile in dorsal view broadly rounded or slightly angular, widest point of stalk1/6to ¼ the length of stalk from base; basal tuberosities well developed and medially confluent, in end-view dorsally convex, or at least less deeply concave than ventrally; shaft straight, base bent ventrally or more commonly dorsally; at mid-point of stalk wider than high, often twice as wide as high; viewed from above, lateral profile from point of greatest breadth to middle of shaft a gradual sigmoid curve; slight terminal inflation of shaft.
Specimens examined: Forty-one, of three subspecies;Microtus ochrogaster haydeni, Muir Springs, 2 mi. N, 2½ mi. W Ft. Morgan, Morgan Co., Colorado, 74995, 74998, 74999, 75002; 1 mi. W Laird, Yuma Co., Colorado, 57304, 76833; 2 mi. N, 2 mi. W Haigler, Dundy Co., Nebraska, 75016; 2 mi. S Franklin, Franklin Co., Nebraska, 75043, 75044; Atwood, Rawlins Co., Kansas, 75020, 75023, 75025, 75027, 75028; 1 mi. N, 2 mi. E Oberlin, Decatur Co., Kansas, 75030, 75032, 75034, 75035, 75036; 1½ mi. N, ¼ mi. E Norton, Norton Co., Kansas, 68327; 1 mi. SW Norton, Norton Co., Kansas, 75037; 2 mi. S, 1 mi. W Norton, Norton Co., Kansas, 75038;M. ochrogaster ochrogaster, Rydal, Republic Co., Kansas, 75047-75053, 75060, 75062, 75063, 75066, 75070, 75071, 75073; 1 mi. N, 1 mi. W Holton, Jackson Co., Kansas, 75077; 2 mi. W Court House, Lawrence, Douglas Co., Kansas, 76832; Univ. Kansas Natural History Reservation, Douglas Co., Kansas, 68536;M. ochrogaster taylori, Meade County State Park, Kansas, 68539, 68542.
Figs. 27 and 28
Baculum: Stalk broad, greatest length (2.5 to 2.7 mm.) 12/3times greatest breadth, 4 times greatest depth; median process ossified, size small,1/5length of stalk, higher than wide, having small anterodorsal prominence in both specimens examined; lateral processes cartilaginous, relatively small, displaced posteriorly, attenuate; posterior margin in dorsal view broadly rounded, or having blunt median apex, convex throughout; basal tuberosities moderately well developed, medially confluent, barely visible in dorsal view when mature; in end-view median constriction4/5greatest depth, ventral concavity deeper than dorsal concavity, both comparatively shallow; stalk at mid-point 1½ times as wide as deep; shaft relatively slender, bowed dorsally at tip, relatively straight otherwise; lateral profile in dorsal view a gradual concave slope from point of greatest width anteriorly to distal part of shaft.
Specimens examined: Two, from Douglas Co., Kansas, 76834 (2 mi. N Baldwin), 68545 (1 mi. NE Pleasant Grove).
Fig. 40
Baculum: Stalk broad, greatest length (2.4 mm. in specimen examined) 1¾ times greatest breadth, 4 times greatest depth; median process ossified, size small, less than ¼ length of stalk, wider than high, terminally flattened; lateral processes cartilaginous, relatively small, attenuate; posterior margin in dorsal view flattened, irregularly curved with concavities medially and laterally; basal tuberosities well developed, medially confluent; visible in dorsal view; in end-view median constriction2/3greatest depth, ventral concavity well-formed, no dorsal concavity; stalk at mid-point twice as wide as deep; shaft relatively slender, bowed dorsally toward tip; in dorsal view lateral profile a gradual concave slope from point of greatest width anteriorly to distal part of shaft; tip of shaft enlarged.
The baculum ofM. parvulusresembles that ofM. pinetorummore than it resembles the baculum of any other microtine studied, differing primarily in smaller size.
Specimen examined: One, from 1 mi. W Micanopy, Alachua Co., Florida, Univ. Florida No. 1508.
Figs. 29 and 30
Baculum: Stalk broad, greatest length (2.6-3.2 mm.) 11/3to 12/3times greatest breadth, 31/3to 32/3times greatest depth; median process ossified, with ventral depression, process ¼ to1/3length of stalk, appressed to tip of shaft, wider than high proximally, relatively broad terminally; lateral processes cartilaginous, small, attenuate; posterior profile of stalk in dorsal view broadly rounded, bilobate, or trilobate, median lobe formed by posterior projection of dorsal shelf between enlarged lateral tuberosities that form outer lobes, posterolateral faces of these tuberosities visible in dorsal view of stalk; in end-view dorsal surface slightly concave, ventral concavity broad and deep, median constriction½ greatest depth; shaft flattened except tip that is more terete, and bowed dorsally; at mid-point, stalk twice as wide as high; shaft relatively slender terminally, narrower than median ossification.
The baculum ofM. quasiateris the largest and has the best developed base and median process of the three American species of the subgenusPitymys. The three species closely resemble each other in basic form.
Specimens examined: Five, all from Veracruz; Teocelo, 4500 ft., 30709, 30711; 4 km. N Tlapacoyán, 1700 ft., 24466; 5 km. N Jalapa, 4500 ft., 19869, 19878.
Fig. 26
The baculum of a single specimen (KU 67103) ofM. fatioifrom Zermatt, Valais, Switzerland, was examined. The baculum is immature, as evidenced by its small size, slender stalk and absence of ossified processes, therefore no characterization is included.
The baculum of another Old World species of the subgenusPitymys,M. pyrenaicusfrom France, figured and described by Didier (1954:242-243), differs from all New WorldPitymysexamined in processing ossified lateral processes.
The status ofPitymys, as a genus or as a subgenus, is uncertain. Hall and Cockrum (1953:448) considered the North AmericanPitymysandPedomysas subgenera ofMicrotus. They did not state specifically the basis for this point of view, but mention the fact that these two subgenera (PitymysandPedomys) closely resemble each other cranially. These authors did not study nor comment upon the status of the Old WorldPitymys. It may be asked whether the Old World and New WorldPitymyshave developed as fossorialMicrotusindependently, or from an ancestor common to both groups and not common to any otherMicrotus. Matthey (1955:202) found 62 chromosomes (2N) in both the New WorldPitymys pinetorumand the Old WorldPitymys duodecimcostatus. This suggests, but does not prove, common ancestry.
Fig. 49
Baculum: Stalk massive, greatest length (4.7 mm.) 1¾ times greatest breadth, 4 times greatest depth; ossification in digitate processes variable; in one (KU 27123) of two specimens examined lateral processes ossified and median process unossified, as in two specimens examined by Hamilton (1946:379) from "southern Florida"; in my other specimen (KU 27268) that is possibly more mature, median process ossified although less deeply stained than lateral ossifications or stalk; posterior profile in probable dorsal view roughly rounded; in end-view probable dorsal concavity deep, ventral concavity broad but shallow, and with center convex; median constriction3/5greatest depth; shaft heavy, least depth2/3greatest depth of base; stalk, at mid-point, slightly wider than deep and more than1/3width of base; lateral profile in dorsal view sharply incurved distal to point of greatest breadth, shaft therefore relatively distinct from basal part of stalk; slight subterminal constriction; tip less reduced in the two specimens examined than in two figured by Hamilton. In preparation, the tissues that make it possible to distinguishwith certainty the dorsal and ventral surfaces of the baculum were removed in both specimens.
Specimens examined: Two, of the subspeciesNeofiber alleni alleni, 2 mi. S Gainesville, Alachua Co., Florida, 27268; 1 mi. E Courtenay, Merritt Island, Brevard Co., Florida, 27123.
Fig. 46
Baculum: Stalk slender, greatest length (2.5 mm.) 2 to 22/3times greatest breadth, 4 to 5 times greatest depth; three ossified processes; median one more than1/3length of stalk, curved dorsally toward tip, proximally flattened and having acute lateral angles in dorsal view, wider than deep except in distal half; lateral processes smaller than median one, slenderer, shorter, of approximately same depth, also curved dorsally; base of stalk well developed, basal tuberosities medially confluent, in part visible in dorsal view, in end-view wider ventrally than dorsally, dorsal and ventral concavities of equal depth and both wide, medial constriction ½ greatest depth; posterior profile in dorsal view broadly bilobate; lateral profile with abrupt transition from basal tuberosities to gradually converging, slightly curved sides of shaft; shaft terminally inflated.
Dearden (1958:543) described and figured the bacula of six subspecies ofLagurus curtatusand two Asiatic species,Lagurus lagurusandLagurus luteus. He examined at least 34 specimens ofL. curtatusand found geographic variation in size, breadth of shaft distally, and proportions of digital ossifications to each other and to the stalk. The description that I have given above pertains toL. c. levidensis.
The baculum of the AsiaticLagurus (Lagurus) lagurusfigured by Ognev (1950:554) agrees with that ofLagurus (Lemmiscus) curtatus, described here, in the relatively elongate shaft and slender stalk, the proportions of the processes, and the well-formed and moderately enlarged base of the stalk. The bacula of threeLagurus lagurusexamined by Dearden (1958:545) were of older individuals than the specimen that Ognev figures and differ from it and from bacula ofLagurus curtatus(all subspecies) in the unusual, almost heart shaped, median process, and in larger size.Lagurus luteusexamined by Dearden (1958:545) differs from bothLagurus lagurusandLagurus curtatusin lacking lateral digital ossifications and in having shorter median digital ossifications and wider base of stalk.
Specimens examined: SevenLagurus curtatus levidensisfrom Wyoming; 9 mi. S Robertson, Uinta Co., 26045, 26053; 8 mi. S, 2½ mi. E Robertson, Uinta Co., 26049; Farson, Sweetwater Co., 37906; 16 mi. S, 11 mi. W Waltman, Natrona Co., 42457; 32 mi. S, 22 mi. E Rock Springs, 42465, 42466.
The following key to the bacula in some adult North American Microtinae is intended to help point out some of the most important differences. It should be noted that not all species can be keyed out on the basis of the baculum. The most difficult group in this respect includes the species ofMicrotusthat have small or no ossified lateral processes, especially species of the subgeneraPedomysandPitymys, and the two speciesMicrotus californicusandMicrotus mexicanusof the subgenusMicrotus. Another complicating factor is the variability of bacula evident in some species even in the small samples available.It is to be expected that additional specimens will show variations not yet observed.
Owing to shortness of lower incisors and present geographic distribution of the species, Hinton (1926:35) considered the Tribe Lemmi (lemmings) to be more primitive than the Tribe Microti (voles). The surviving lemmings are specialized in many features and therefore are considered as advanced end-products of an evolutionary radiation of a primitive microtine stock, of which all earlier stages are extinct.
Hinton regardedDicrostonyxas the most primitive of the genera of lemmings on account of its more complex molar teeth (complexity was considered to be primitive), and on account of the presence of three primitive longitudinal rows of tubercles in unworn molars. The other three genera were arranged in order of increasing specialization as follows:Synaptomys,Myopus,Lemmus.
If the baculum tended to retain its primitive character while specializations in the external anatomy developed, and if the above arrangement is correct the most primitive bacula would be found inDicrostonyxand inSynaptomys. The baculum in these two genera in comparison to that inMyopus(as figured by Ognev, 1948:512)andLemmushas a slenderer stalk and smaller digital ossifications or none at all. The baculum in the genera of lemmings increases in robustness and the development of processes fromDicrostonyx, toSynaptomys, toMyopus, toLemmus—the same order outlined above for total of specialization. The two extremes in this series are near the extremes of variation in bacula to be found in all microtines. The baculum in lemmings as a group cannot then be considered more primitive than in voles as a group, although the voles are usually considered to be more advanced. The situation in the voles, as we shall see, casts a different light on the matter.
The voles, Tribe Microti, were considered by Hinton (1926:40) to be more advanced than the lemmings because the incisors of the voles are longer and the root of their last lower molar is lingual to the root of the incisor. Hinton thought also that the murine ancestors of microtines had shorter incisors and that the backward extension of the incisors in the voles is a more ancient feature than the hypsodonty of the molars. A trend in the molar teeth has been toward greater hypsodonty. The voles in which the molars are least hypsodont are thus considered primitive. These include the living generaClethrionomys,Phenacomys,Ondatra,Dolomys,Ellobius, andPrometheomys. Therefore, the baculum, in these assumedly primitive genera, would be expected to resemble the baculum in the lemmings or at least the most primitive lemmings. This is not the case.
The bacula that I have examined ofClethrionomysandPhenacomyshave well-developed digital ossifications. In this they resemble the baculum of the genusLemmus, the most advanced genus of lemmings according to Hinton. The baculum ofDolomyshas not been studied. The baculum inOndatra, and inPrometheomysas illustrated by Ognev (1948:552), also possesses well-developed processes. The baculum ofEllobiusis small and lacks processes (as figured by Ognev, 1950:662). No ossification was found in a single specimen ofEllobiusexamined by me although the entire glans penis was removed and cleared without dissection. So far as known then, with the exception ofEllobiusandPhenacomys longicaudus(Dearden, 1958:547), the primitive microtines having rooted molars possess bacula having three well-developed ossified processes.
Voles of the genusMicrotusvary in the structure of the baculum almost as much as do the lemmings. Within the single subgenusMicrotussome individuals ofMicrotus mexicanus, for example, have minute ossified lateral processes and other individuals lack theseprocesses;Microtus pennsylvanicusand some other species have proportionately large lateral ossifications. If the well-developed condition of the baculum in the microtines having rooted molars is primitive, then within the genusMicrotusthose species having well-developed bacula may be considered primitive.
The generaLagurusandNeofiberhave moderately developed or well-developed lateral processes.Neofiberexhibits a tendency, not prominent elsewhere, to have a proportionately smaller median process rather than reduced lateral processes.
American species ofMicrotus(genus and subgenus) that have moderately- to well-developed ossified lateral processes areM. townsendii,M. oeconomus,M. pennsylvanicus,M. montanus, andM. chrotorrhinus.Microtusof other subgenera having this type of baculum includeM. (Herpetomys) guatemalensis,M. (Chilotus) oregoni, andM. (Chionomys) longicaudus.
American species ofMicrotus(genus and subgenus) in which the lateral ossifications are weakly developed or absent (although cartilaginous lateral processes are present) includeM. mexicanusandM. californicus. In other subgenera, species ofMicrotushaving reduced lateral ossifications areM. (Pedomys) ochrogaster,M. (Pitymys) pinetorum,M. (Pitymys) parvulus,M. (Pitymys) quasiater,M. (Arvicola) richardsoni, andM. (Stenocranius) miurus.
The microtines are essentially holarctic in distribution. Both of the tribes, the lemmings and the voles, as well as primitive representatives of each tribe (not consideringEllobius) occur in both the Old World and New World. It is not certain on which continent (or continents) the Microtinae first differentiated. It is certain, however, that at various times, both early and late in the evolution of the subfamily, representatives have crossed from Eurasia to North America orvice versa. Each of 10 or more microtines in the New World is more closely related to some microtine in the Old World than to any other microtine in the New World.
The similarities or differences in the baculum in Old World and New World representatives placed in the same genus or subgenus, or thought to be "companion species" have been commented upon in accounts ofLemmus,Dicrostonyx,Clethrionomys,Lagurus,Arvicola,Stenocranius,Chilotus,Chionomys,Pitymys, and in accounts ofMicrotus agrestisas compared withM. pennsylvanicus, andMicrotus oeconomus(both Old World and New World).
The baculum in the Microtinae more closely resembles the baculum in the Cricetinae of the Old World than in the Murinae, or than in any other rodents known to me. This resemblance suggests relationship between Microtinae and Cricetinae.
28-774
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