From 1967 to 1974 a number of human cranial and postcranial remains were unearthed with many animal bones from limestone fissure deposits at the Minatogawa quarry near the southern coast of Okinawa Island, Japan. The mammalian fauna from this site includes two extinct species of deer, Cervus astylodon and Muntjacinae, gen. et. sp. indet. (Hasegawa, 1980). However, the fissure deposits, as is usually the case, have yielded no signs of human occupation nor typologically well-defined artifacts. In such an instance, chemical changes in some organic or inorganic elements in phosphatic skeletal material sometimes provide chronological information (Oakley, 1969; Matsu'ura, 1978; and others). Fluorine, which accumulates in buried bone over a period of time, has received the most attention, and the fluorine dating method (Oakley, 1951) has been applied to many fossil hominids to clarify their stratigraphical ages (e.g. Bergman and Karsten, 1952; Oakley, 1954; Tanabe, 1966). This report is an assessment of the relative antiquity of Minatogawa Man deduced through fluorine determination.

MATERIALS AND METHOD

Samples from crania I, II, IV, mandible A, and four other postcranial bones of the Minatogawa man were submitted to fluorine determination. A series of boar fossils (Sus leucomystax taivanus ?) and deer fossils (Cervus astylodon and Muntjacinae, gen. et sp. indet.) was used for comparison. Two samples of Holocene human remains (approximately 2,000 years B.P.; Suzuki, H., personal communication) from the Chibana quarry near Minatogawa were also taken for comparison.

A small piece of a transverse section of Substantia compacta cut from each specimen was thoroughly scraped to remove surface dirt, and then pulverized in an agate mortar. Approximately 15 mg of the bone powder was weighed to ±0.05 mg and dissolved in 10 ml 1M HCl. Then the ionic strength of the sample solution was fixed by adding 30 ml of a buffer which was prepared according to TISAB IV (see Orion Inc., 1977) with modulation for this assay. The buffered system has final concentrations of 0.5 M HCl, lM TRIS and 0.5 M NaTartrate. Fluorine concentration was determined using a fluoride electrode by reference to a standard curve calibrated with several NaF standards of the same ionic strength and pH as the sample solution. A known addition was used to verify the direct measurement result. Details and discussions of the analytical method are given by Matsu'ura (1981).

RESULTS AND COMMENTS

Listed in Table 6. 1 are the resulting data for fluorine analysis. The wild boar specimens show varying fluorine content, from 0.57% to 1.52%. The fluorine measurements of deer fossils, on the other hand, locate in a range comparable to the upper half of that for boar. The difference between the two groups is highly significant (p<0.001) by Mann-Whitney U-test. The dispersion of fluorine in the boar specimens implies that they are of a wide age range.

As Fig. 6. 1 shows, the boar bones from the upper deposit (Level 1-4) are grouped around 0.8% F, whereas those from the lower deposit (Level 5-8) appear to be in two separate groups. It is worth noting that the six boar specimens with high fluorine content from the lower deposit are found to have a light color on the surface, and the other boar specimens are dark grey or brown. This finding together with the fluorine analysis results may indicate that three of the nine fossils which were found at the lower deposit are probably intruders from an upper horizon.

The above results would introduce a hypothetical but plausible classification of the mammalian fauna into two phases :
Phase a, wild boar and two extinct species of deer;
Phase b, wild boar (deer nonexistent).

As to the hominid specimens, seven out of the eight measurements fall within the range of deer fossils (Fig. 6. 1); this suggests that the Minatogawa man is to be referred to Phase a and possibly even to the transitional phase from a to b, presumably dating back to Late or End Pleistocene.

The provisional conclusion that the Minatogawa man lived in the Pleistocene seems to be supported by its high. fluorine content, which contrasts with that of the Holocene human remains from Chibana; however, it must be acknowledged that the effect of such important circumstances as prevailing hydrological conditions has not been taken into account. Charcoal fragments from the lower deposit of the Minatogawa site have yielded radiocarbon dates of 18,250±650 yr B.P. (TK-99) and 16,600±300 yr B.P. (TK-142), but future research must yet establish their time-relation to human fossils.

Further studies on the chronology for the Minatogawa man and other Pleistocene man in the Okinawa District should be conducted using various techniques. The amino acid racemization dating (Bada and Schroeder, 1975; Bada et al., 1979; Matsu'ura and Ueta, 1980 a, b; and others) would be particularly promising for this region with its mean annual temperatures above 20°C.

ACKNOWLEDGEMENTS

The author is much indebted to Professor H. Suzuki for suggesting this investigation as well as for preparing the samples of human bones from Minatogawa and Chibana, and to Professor Y. Hasegawa and Messrs. K. Ono and H. Nogariya for supplying and identifying the animal specimens for the study. Thanks are also due to Miss A. Nakatsuka for the drafting of Fig. 6. 1.

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