63. 日本産化石馬に就いて

Fossil equid remains are very rare in the Japanese Islands, probably owing to the particular land condition that prevailed during the later Cenozoic, whic-ch is adverse to the life of equids and on the contray favourable to that of Proboscidea. In Middle Pleistocene, some Manchurian or North Chinese elements evid-ently migrated into the land, as such remains are found in the Upper Kuzuii bed-s of Totigi prefecture, the sand and gravel bed of the Inland sea, and the Tuki-noki asphalt bed of Akita prefecture. The last mentioned deposit, yielded the equine tooth now under consideration; other mammalian remains previously describe-d from the same deposit are Palaecloxodon namadicus yabei (MATSUMOTO), Sus nipp-onicus nipponicus MATSUMOTO, Cerrus (Sika) ezoensis HEUDE, and Canis sp. This occurrence, the writer thinks, indicate that some steppe animals might have invad-ed into the Japanese Islands in association with the other Manchurian elements. The very fragmental equine tooth from the asphalt bed, about 22mm long, 23mm wide and 31mm high, probably belonged to a median-sided equid; it has a flat protocone as in E. przewalskii POLIAKOFF or E. caballus LINNE, and relatively weak en-amel plication, weaker than in E. sanmeniensis TEILHARD and PIVETEAU or in E. leptostylus MATSUMOTO. The fossil remain may represent a species perhaps allied w-ith E. hemionus or other small sized equids. Another tooth, shown in Fig. 1 b i-s a left lower last molar, about 30mm long, 12mm wide and 43mm high; it is quit-e similar to the corresponding one of E. caballus. It was found lying on the sa-ndy shore near Hitati-mati, Ibaraki prefecture; it may be a fossil or subfossil, or even its being aquite recent one is by no means excluded. In connection of the respective antiquity and sequence of E. sanmeniensis, E. przewalskii and E. caballus, it is questioned whether the equine tooth from Honan described under the name of E. leptostylus MATSUMOTO is not referrable to E. przewalskii, becaus-e the correspondent tooth of the latter species differs not much from the forme-r in dimensions and enamel plication. Which of the various names-E.(E.) caballus fossilis CUVIER, E.(E.) caballus leptostylus MATSUMOTO, E.(E.) caballus przewa-lskii (POLIAKOFF) and E.(E.) przewalskii POLIAKOFF should properly be applied t-o the Anyan equid which is sometimes regarded to be a domestic form, is a quest-ion difficult to answer. At present wide divergence of opinion exists between t-he American and oriental authors as to the geological age of the Hipparion bed of the Siwalik series; the present writer rather tends to the view held by PILGR-IM or TEILHARD de CHARDIN, as the Americans seems to him to be too arbitrary in regarding the New World as the native land of Hipparion. For intercontinental c-orrelation of fauna, the use of certrain single group of animals instead of the whole fauna may prove to be of considerable value, though sometimes quite dange-rous. Beside the two specimens cited above, there are some others which have pr-eviously been reported by Dr. TOKUNAGA, namely several specimens of E. caballus from Keisei, Tyosen, and Kuroi village in Hyogo prefecture; farther there are s-everal remains from Neolithic sites reported by Dr. HASEBE, especially of Kyush-u, which specially attracted his attention to the small size of them. Hence one can at least safely express that some small sized horses lived in Japan from th-e Middle Pleistocene of the Neolithic age, contemporaneous with Sus nipponicus MATSUMOTO. The small size may be interpreted cither as its specific character or as due to island life.