再び本州中部山地の鼠類に就て Clethrionomys rufocanus andersoni (THOMAS)と其分類の考察

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  • Supplementary Notes on Muridae in the Highlands of Central Japan: On Clethrionomys rufocanus andersoni (THOMAS) and its Taxonomical Status

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While engaged in investigating the ecological distribution of small mammales on the lofty mountains in Central Japan, in August 1937, I made some good collections of Clethrionomys in the timber zone (alt. 1900 m to 2400 m) and the herbaceous zone (2400 m to near the summit) of Mt. Yatsugatake (2899.2 m). The detailed measurements of external bodies and craniums are shwon in Table 1. These specimens are identified externally as Clethrionomys rufocanus niigatae, in having very long tails and light brown mantles, but in studying the many skulls, I suddenly impinged upon the fact that some skulls were almost indentical with those of the Clethrionomys rufocanus andersoni, though some of rest were allied to C.r. niigatae. Such a difference is probably due to the different ages of the species. Therfore, to ascertain this I took up two skulls which were most nearly like the types of C.r. andersoni and C.r. niigatae, in condylo-basal length-No. 149 skull (condylo-basal length 26.1 mm) for the type of C.r. andersoni (25.7 mm); No. 144 skull (25. mm) for the type of C.r. niigatae (25.4 mm)-and compared them with the photographs of types in HINTON'S monograph^<1)>. The No. 149, shown in the plate, nearly agrees with the type of Clethrionomys rufocanus andersoni in having rather longer skull, longer rostrum, longer and parallel interorbital region and relatively longer and rectangular brain case than in the type of C.r. niigatae. On the other hand, No. 144 closely resembles the type of C.r. niigatae in having rather short but wider skull, shorter but wider rostrum, wider and less parallel interobital region, and less angular brain case-these characteristics were described by ANDERSON as the distinctive points of C.r. niigatae from C.r. andersoni. The differences between No. 149 and No. 144, in shape and structure of skull and cheek teeth, are due to the differences of the age and nothing else, for both skulls were picked up in the same uniform series of specimens which have a similar external character. According to the original descriptions, there are some external differences between C.r. andersoni and C.r. niigatae, i. e., in colour, size, and length of tail. But as to colour, I find namy variations not only individually but also of the age. The large body and short tail of THOMAS' C.r. andersoni may also be an individual variation, because the specimen which can be strictly identified as C.r. andersoni has not yet been found in any part of Japan except a type and a specimen described by THOMAS in 1905. So that these external differences do not give the slightest support to distinguish them one from the other. Consequently, C.r. andersoni and C.r. niigatae are one and the same and as the latter was predated by the former, C.r. niigatae becomes the synonym of C.r. andersoni^<2)>. C.r. andersoni (=C.r. niigatae) differs from C.r. smithii and C.r. bedfordiae in the following respects: 1) Comparing the same-sized skulls of each subspecies one by one, C.r. andersoni is apparently lightly built in the structure of skull, but shows more developed angular appearance than C.r. bedfordiae. But it is more strongly built than C.r. smithii, having larger, more round and less angular brain case, more robust but less extended zygomatic arcs, and shows a relatively juvenile appearance. It is also conspicuous that the auditory bullae of C.r. andersoni are moderately larger and more round than others. As for the molars, C.r. andersoni has median size between C.r. smithii and C.r. bedfordiae with more sharp salient angles than C.r. smithii but less sharp than C.r. bedfordiae. 2) In the external character, the long tail of C.r. andersoni, on the whole, may-become a distinguishing point as shown in Fig. 3. 3) These three forms are distributed respectively in different parts of Japan, i. e., C.r. bedfordiae in Saghalien and Hokkaido, C.r. andersoni in the northern part of N. 36° in Hondo and C.r. smithii in the remaining regions of Japan proper.

収録刊行物

  • 動物学雑誌

    動物学雑誌 49 (12), 429-436, 1937-12-15

    東京動物學會

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