Minatogawa Research Articles

Relative chronology of the Minatogawa and the Upper Minatogawa series of human remains from Okinawa Island, Japan

A series of human fossils, the so-called ‘Minatogawa Man’ material, unearthed from the fissure site at the Minatogawa limestone quarry on Okinawa Island, is well known as the best preserved Pleistocene human remains in Japan. Another series of ‘Upper Minatogawa’ human remains was also recovered from the same fissure site. Although the Upper Minatogawa series was supposed to be derived from higher horizons than the Minatogawa series, and this supposition was provisionally supported by the fluorine dating of bones, the chronological and/or stratigraphical relationships of individual human specimens have nevertheless not been clarified. Here we report newly obtained data on the relative chronology of the Minatogawa and the Upper Minatogawa series by additional element analyses (strontium and barium) of bones, and draw the following inferences: (1) the Upper Minatogawa human remains are younger than the Minatogawa human remains (i.e. ‘Minatogawa Man’) as a group; (2) however, a wider age range is implied for the ‘Minatogawa Man’ series, and some of the specimens such as Minatogawa IV and maybe Minatogawa II are comparable in age to the Upper Minatogawa series. Thus, the ‘Minatogawa Man’ series may not comprise a single chronological group, although they may be of one morphological group. We also discuss the geological age of the Minatogawa fossil assemblages, and address preliminary palaeoanthropological implications concerning the population history of the Japanese archipelago in the Late Pleistocene.

The origin of Homo floresiensis and its relation to evolutionary processes under isolation

Since its first description in 2004, Homo floresiensis has been attributed to a species of its own, a descendant of H. erectus or another early hominid, a pathological form of H. sapiens, or a dwarfed H. sapiens related to the Neolithic inhabitants of Flores. In this contribution, we apply a geometric morphometric analysis to the skull of H. floresiensis (LB1) and compare it with skulls of normal H. sapiens, insular H. sapiens (Minatogawa Man and Neolithic skulls from Flores), pathological H. sapiens (microcephalics), Asian H. erectus (Sangiran 17), H. habilis (KNM ER 1813), and Australopithecus africanus (Sts 5). Our analysis includes specimens that were highlighted by other authors to prove their conclusions. The geometric morphometric analysis separates H. floresiensis from all H. sapiens, including the pathological and insular forms. It is not possible to separate H. floresiensis from H. erectus. Australopithecus falls separately from all other skulls. The Neolithic skulls from Flores fall within the range of modern humans and are not related to LB1. The microcephalic skulls fall within the range of modern humans, as well as the skulls of the Neolithic small people of Flores. The cranial shape of H. floresiensis is close to that of H. erectus and not to that of any H. sapiens. Apart from cranial shape, some features of H. floresiensis are not unique but are shared with other insular taxa, such as the relatively large teeth (shared with Early Neolithic humans of Sardinia), and changed limb proportions (shared with Minatogawa Man).

Inconsistency of the maxilla and mandible in the Minatogawa Man No. 1 hominid fossil evaluated from dental occlusion

The Minatogawa man hominid fossils are human fossils from Japan and the oldest from the Late Pleistocene period. Of the Minatogawa skeletal remains, Minatogawa Man No. 1 is best preserved and is accompanied by the mandible. When the maxillary and mandibular dentitions of Minatogawa Man No. 1 were occluded, the dentitions did not align with one another. The attrition pattern of the maxillary teeth was of an inclined type, which tilted from the buccal to lingual side, whereas that of the mandibular dentition was of a horizontal type. Moreover, both left maxillary and mandibular third molars exhibited attrition on the distal portion of the occlusal surface. The occlusal surfaces did not complement each other in the range of mandibular movement without temporomandibular joint dislocation and the curve of Spee produced by the left maxillary and mandibular occlusal planes did not match. These findings suggest that the maxilla and mandible of Minatogawa Man No. 1 are, in fact, from different individuals.

Physical Adaptation of the Minatogawa People to Island Environments

港川人骨は故・大山感保氏によって1970 年に沖縄県具志頭村港川採石場で発見された4 体分+α の化石骨格である。時代は17,000 年ほど前であり，アジアの新人化石として最も保存が良い。以下，代表として1 号男性について述べる。 脳頭蓋は低く広く頑丈であり，骨壁が厚いので，外見のわりには頭蓋腔容積は小さい(1,390ml) 。顔面も低く広く造りがごつい。眉聞が出っぱり，鼻根はくぽむが鼻梁は高く立体的である。顎の骨の歯槽部が厚く，歯の唆耗は激しい。口元は引き締まっていて，顎先(オトガイ)はしゃくれた感じはしなかった。側頭筋のはいる側頭窩が非常に深く，頬骨が強く張りだすので，側頭筋や唆筋の発達は極めて良かったはずである。下顎底は弓状で，いわゆる「揺り椅子」状態。 四肢躯幹骨は小柄である(推定身長は153 em) 。特に鎖骨と上腕骨が華脊であり，肩や腕は弱かったといえる。しかし，手は大きいので鍾カはかなり強かったらしい。下肢の骨の頑丈さは体のサイズに合っている。足は大きいので，山野を歩き走るには適していたようである。 港川人のこのような特徴は，食物の大部分が硬く粗雑で，あまり栄養状態の良くない，遊動性の採集狩猟生活に対する適応，すなわち具体的には島嶼環境への適応と理解するのが適当である。 同時代の東アジアの化石である山頂洞人や柳江人そして縄文時代人は，脳頭蓋や顔面の特徴においては港川人と共通する部分があるが，日且鴫筋の発達程度は弱い。ただし，四肢躯幹骨の特徴では，彼らと港川人は全く異なっている。山頂洞人・柳江人・縄文人とも，大腿骨後面の粗線が発達して付柱状になるなど，全身の筋肉の発達が伺える。つまり，彼らは比較的良好な栄養状態のもとで，筋肉が発達するような適度な労働をしていたといえよう。定住(多寡はあるが)を含んだ広く多様な活動をしていたことだろう。 さて，港川人は縄文人の直接の祖先なのだろうか。脳頭蓋と顔面の特徴では，港川人は縄文人とよく似ているので，祖先である可能性は高い。四肢躯幹骨の特徴は全く違うが，それに関しては港川人の島嶼適応という特殊な状況のためとも考えられるので，否定材料としては完全ではない。ちなみに，港川人と同じ時代の本土の断片的な化石四肢骨は，縄文人と同様の特徴を示す。 なお，現代南西諸島人の起源が問題である。港川人から縄文人をへて現代南西諸島人へと変化したのか，それとも周辺からの大量の移住があったのだろうか。埴原和郎の二重構造モデルでは，南西諸島人は港川人・縄文人の直系の子孫と考えられた。一方，高宮広土は，狭い南西諸島で集団を維持してゆくのは困難であり，何度かの絶滅と移住が繰りされた可能性を示唆している。 確かに，最近の人類学的研究では，現代南西諸島人は縄文人やその直系子孫であるアイヌとは異なり，むしろ本土日本人と似ているとの結果が出ている。そうだとすると，縄文時代以降連綿と，南西諸島は日本本土あるいは中国·台湾との聞にかなり頻繁な移住·交流があったと見なす方がよさそうである。

陸橋とヒトと生物の渡来 琉球弧の第四紀古地理

Compilation of seismic reflection profiles, rock sample analyses and manned and non manned diving observations revealed that land bridges, connecting the Ryukyu Arc to the Chinese continent, have appeared in two stages since the late Pliocene. The first stage occurred before the deposition of Pleistocene Ryukyu Limestone and ceased in the early stages of deposition, while the second was apparent during the middle and late stages of the Ryukyu Limestone. The land bridge in the first stage may have appeared between 2.0-1.0 Ma and is well identified by the unconformity between Shimajiri and Ryukyu Groups before the deposition of Ryukyu Limestone. The land bridges may have appeared two or three times in the second stage during or after deposition of Ryukyu Limestone between 0.4-0.02 Ma. The last land bridge may have appeared during the Wurm glacial stage in the late Pleistocene, connecting the Chinese continent through Taiwan, Okinawa and Amami-Oshima to the Kyushu main land. This supports the hypothesis that the Minatogawa Man migrated to Nansei-shoto Islands passing through the land bridge in the Late Pleistocene.

On the Cross Section of Lower Limb Long Bones in Minatogawa Man from Okinawa

The geometric properties of the mid-length cross section of the lower limb bones in Minatogawa man were measured by means of the X-ray non-destructive method to determine their mechanical robustness. The Minatogawa bones were not significantly different from those of recent Japanese, but were not as robust as those of Jomon man of the Middle to Latest period nor as of many fossil man. In Minatogawa man, the No.III female bones had relatively large amount of bone substance and in their shape distance by Penrose were rather similar to some ancient bones.

Morphological Investigation of Innominate Bones from Pleistocene in Japan with Special Reference to the Akashi Man

All the human male innominate bones seemingly from the Pleistocene age were morphologically investigated based on the recent advances in knowledge. New measurement methods were applied to these innominates as well as the available fossil innomimate casts and Recent Japanese innominates for comparison. For this measurement and observation new casts were made from all the fossils and restored so as to presume the whole form of the ilium. Some of the multivariate analyses were used for the objective comparison. The results indicate that the Akashi man is comparable neither to Erectus nor to Neanderthal nor to Pleistocene Sapiens but to modern Sapiens, whereas the Minatogawa man and the Mikkabi man are in many respects archaic and seem certain to be the Pleistocene Sapiens.

りゅう球列島の後期更新世〜完新世のせきつい動物

The mammalian fauna of Okinawa in the period from Late Pleistoceneto Recent is discussed. The Ryukyu Islands are known for abundant occurrence of deer fossils of Miocene type. The Yamashita-cho site of fossil man, 32, 100±1, 000y.B.P. (TK-78) in age, yields deer fossils and no other mammals. On the other hand, at the site of the Minatogawa man, 18, 250±650y.B.P. (TK-99) to 16, 600±300y.B.P. (TK-142) in age, deer fossils become few while boar fossils increase remarkably. This indicates that the Ryukyu boar gained ground taking the place of deer.Wild boars are living in such islands as Amami Oshima, Okinawa, Ishigaki and Iriomote, and many shell-mounds reveal the existence of boar. In all probability, migration of Sus must have taken place since the time of the Minatogawa man, that is, during the Wurm maximum. Geologically the Ryukyu Islands are supposed to have been already separated from the continent at that time, but the occurrence of Sus suggests that the islands were partly connected with the continent even in the Wurm maximum.