第 四 紀 研 究(The Quaternary Research) 43 (3) p. 169-180 June 2004 A New Specimen of Palaeoloxodon naumanni from Hokkaido and its Significance Keiichi Takahashi*1, Yuji Soeda*2, Masami Izuho*3, Kaori Aoki*4, Goro Yamada*2 and Mono Akamatsu*2 This paper describes a new-discovered upper right second molar of Palaeoloxodon naumanni from Yubetsu, Hokkaido, that was found in August 1998, and suggests that alternating migration of two kinds of proboscidean, Mammuthus primigenius and Palaeoloxodon naumanni, took place there in relation to climate change. 14C dating of the root of the molar gives an age of 30,480±220yrs BP(measured 14C age). Although the fossil molar was found loose, geological investigations suggest strongly that it derives from a peaty silt bed distributed around ravine in which the fossil was found. This bed includes the Ds-Oh (Daisetsu-Ohachidaira) volcanic ash of 30ka. Judging from the ages and vegetations of the formations from which P. naumanni or M. primigenius remains have been found in Hokkaido, vegetation change controlled by global climate change seems to have affected the migration of the two kinds of proboscidean into Hokkaido. The discovery of P. naumanni remains of 30ka in Hokkaido suggests the possibility of a northward re-migration of P. naumanni from Honshu during the MIS 3. Keywords: Mammuthus primigenius, Palaeoloxodon naumanni, climate change, MIS 3, Hokkaido, Late Pleistocene thus primigenius. I. Introduction In this paper, the Yubetsu specimen is de- In August, 1998, after heavy rains, brothers scribed, and alternating replacement of two Hiroshi and Yasushi Yokoyama were walking kinds of proboscidean, MMprimigenius and P. in a forest in Higashi-baro, Yubetsu, Hokkaido, naumanni, in the northern part of the Japanese looking for edible wild plants. During their Islands is discussed in relation to climatic fluc- search, they found a proboscidean molar in a tuations in the Late Pleistocene. brook (Fig. 1). Thereafter, H. Yokoyama do- II. A note on stratigraphy nated the specimen to the Yubetsu-cho Board of Education. Subsequent studies of the speci- Stratigraphical description of the site of men and a geological survey at the site have occurrence: revealed that the molar fossil is assignable to The Yubetsu specimen was found in a small Palaeoloxodon naumanni and its age is about 30 lying in a small ravine about 150m long (Fig. 1, ka. This specimen is much younger than finds Loc. a). Almost no rock outcrop is present in or of P. naumanni previously reported in Hok- along side the brook, where the land surface is kaido, being within the age range of Mammu- covered with vegetation and talus deposits. On Received July 9, 2003. Accepted February 21, 2004. *1 Lake Biwa Museum . 1091 Oroshimo, Kusatsu, 525-0001, Japan. E-mail: *2 Historical Museum of Hokkaido . 53-2 Konopporo, Atsubetsu, Atsubetsu-ku, Sapporo, 004-0006, Japan. *3 Sapporo Buried Cultural Property Center . Minami 22, Nishi 13, Chuo-ku, Sapporo, 064-0922, Japan. *4 Geological Survey of Japan , AIST. Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan. 170 Takahashi, K., Soeda, Y., Izuho, M., Aoki, K., Yamada, G. and Akamatsu, M. June 2004 the sidewall of the ravine through which the gravel layer, a primary fall unit of fine volcan- brook runs, about 10m downstream from the ic ash layer (Ash 1), a peaty silt layer, and a fossil locality (Fig. 1, Loc. b), the strata are par- rounded gravel layer (Fig. 2, Column b). Par- tially visible. The outcrop section at Loc. b ticularly, the volcanic ash layer is an important (Fig. 1) reveals several sedimentary units, marker for understanding the stratigraphic listed in ascending order: a subangular small- correlation and for determining the age deter- mination of the deposits in and around the occurrence point of this fossil molar. Fig. 1 Locality map of the Yubetsu specimen Topographic maps are from 1:50,000 maps of "Engaru" by Geographical Survey Institute of Japan. Fig. 2 Columnar sections of Locs. a and b (Fig. 1) 2004年6月 Palaeoloxodon naumanni from Hokkaido and Its Significance 171 An artificial outcrop was excavated near the as Aoki and Arai (2000). fossil molar locality (Fig. 1, Loc. a) to clarify Characteristics of tephra: the strata from which it might have been de- Ash 1 is a well-sorted, crystal-rich ash. The rived. The outcrop is about 2m wide and about maximal length of pumice particles contained 3m high, and the strata were similar to those at in it is about 2-3mm, and that of heavy min- Loc. b (Fig. 1),10m downstream. The sequence erals is 1-2mm. The mineral content is as fol- starts from a basement rock of shale corre- lows: light minerals 69%, orthopyroxene 14 sponding to the Yubetsu Group of Cretaceous %, and amphibole 7%. Volcanic glass shards to Paleogene strata (Tajika and Yahata, 1991), comprising 10% of the content are composed of through a subangular small-gravel bed with white and well-bubbled pumice. The refractive thin, peaty silt layers and a peaty silt bed, to an indices of the minerals are as follows: glass (n) angular gravel bed at the top (Fig. 2, Column a). 1.494-1.505, orthopyroxene (γ) 1.705-1.711, and A thin lens of fine volcanic ash, which has a amphibole (n2) 1.673-1.680. close resemblance to the tephra at Loc. b (Fig. Ash 2 is present as a thin lens. It consists of 1), is recognized in the peaty silt bed (Ash 2). well sorted, fine and crystal-rich ash; volcanic Analysis method of tephra: glass shards are very rare because of weather- The procedure for preparation of samples of ing. The refractive indices of its component tephra was as follows: 1) washing by ultra- minerals are as follows: glass (n) 1.498-1.501. sonic cleaner, 2) grain separation by sieving, orthopyroxene (γ) 1.705-1.710, and amphibole and 3) observation of minerals under a stereo- (n2) 1.672-1.679. These petrographic charac- microscope. Volcanic glass type, glass color, ters resemble those of Ash 1. Therefore, both and mineral composition of Ash 1 were identi- ash layers seem to belong to the same tephra. fied under the stereomicroscope. Correlation of tephra: The refractive indices of volcanic glass There are four marker-tephra layers of Late shards and heavy minerals were measured by Pleistocene age in the study area: Daisetsu- RIMS-2000 as described by Yokoyama and Ya- Ohachidaira (Ds-Oh: Nakamura and Hirakawa, mashita (1986) and Danhara et al. (1992). Major 2000), Shikotsu pumice fall 1 (Spfa-1: Katsui, chemical components of the volcanic glass was 1958), Kussharo-Shoro (Kc-sr: Arai et al., 1986) measured with an electron probe micro-ana- and Toetoko(Tsk: Okumura, 1991). The major lyzer (EPMA), following the same procedures volcanic glass of Ash 1 is characterized by high Table 1 Major element composition of glass shard from Loc. b and Pleistocene marker-tephra samples in the coastal area of the Sea of Okhotsk, eastern Hokkaido 172 Takahashi, K., Soeda, Y., Izuho, M., Aoki, K., Yamada, G. and Akamatsu, M. June 2004 K2O content and low Na2O, TiO2, and FeO* con- remains. Age determination of the Ds-Oh tent (Table 1). These chemical characters most tephra will be a subject for future research, but closely resemble Ds-Oh among the four mark- we can safely conclude that there are some er-tephras. Furthermore, Ash 1 differs from strata of the latest Pleistocene sediments there, both Kc-Sr and Spfa-1 in mineral composition roughly corresponding to MIS 3. and the refractive indices of its minerals. The age of the fossil molar was measured to Discussion of age of sediments: be 30, 520±220yrs BP (Table 2). This age was The Ds-Oh tephra, a marker of late Pleisto- measured by the AMS method on the basis of cene age, was confirmed around the fossil local- collagen extracted from the tooth root, and we ity. In addition, wood fragments and seeds believe that contamination from modern car- from above and below the Ds-Oh bed at both bon dioxide was avoided. Because the fossil loci were measured by AIMS or by a radiomet- molar was found floating on the surface of the ric method (Table 2), and all materials indicate brook, it is difficult to identify correctly the more than 44,000yrs BP, beyond the measur- original strata in which the fossil was pre- able boundary. served; nonetheless, we assume that the fossil Although the Ds-Oh tephra has been re- molar derived from the peaty silt bed or angu- ported to be as old as about 30ka (Katsui et al., lar gravel bed in the vicinity of the fossil local- 1979; Nakamura et al., 1999; Nakamura and ity. Hirakawa, 2000), all ages of wood fragments III. Description of molar and seeds just above and below both ashes (Ds-Oh tephra) are much older than this. The Proboscidea Illiger, 1881 identification of the Ds-Oh tephra seems to be Elephantidae Gray, 1821 correct, and we cannot explain well this dis- Elephantinae Gray, 1821 cordance of age. It may be that the wood Palaeoloxodon Matsumoto, 1924 fragments were derived from older sediments, Palaeoloxodon naumanni (Makiyama, 1924) such as the lower subangular small-gravel bed Material: Right upper second molar, kept at Loc. a (Fig. 1). by Yubetsu-cho Board of Education, Abashiri- Recently, Machida and Arai (2003) revised shicho, Hokkaido (Fig. 3). the age of Ds-Oh as >30ka, and the age of the Locality: Retrieved from a brook in Hi- just underlying marker tephra, Spfa-1, as 40 to gashi-baro, Yubetsu-cho, Abashiri-shicho, Hok- 45ka.