This paper described crown morphology and sexual dimorphism of the canines in four species of the Great apes; Pongo pygmaeus, Gorilla gorilla, Pan trogrodytes, and Pan paniscus. At lingual view, the contours of maxillary canines in the males had an isosceles triangles with long mesial and distal incisal crests, while those of the females had an equilateral ones. On the other hand, the mandibular canines of both sexes showed a quadrilateral form. In the four species, the mesial shoulder situated closer to the cervical line in the maxillary canine than in the mandibular one. The mesial lingual ridge of maxillary canines runs longitudinally from the cusp tip to the center of cervical ridge, while in the mandibular canines a well-developed distal lingual ridge runs from the cusp tip toward the distal lingual direction in the both sexes. Among the four species, Pongo pygmaeus was characterized by wrinkles on crown surface and a smooth transition between crown and root in males. In Gorilla gorilla, the cervical ridge of the maxillary canine less developed in males, and the notch between the mesial marginal ridge and cervical ridge much developed in the mandibular canine. In the two species of Pan, the distal shoulder of the maxillary canine was situated equal to the mesial shoulder, or closer to the cusp tip than the mesial shoulder in both sexes. In addition, in maxillary canine of Pan paniscus a well-developed distal lingual ridge merged with the cervical ridge, making a L-shaped ridge in both sexes. The sexual dimorphism is significant, not only in size but also in shape and structure of the canine in the four species. The females were characterized as follows: 1) smaller in all sizes, 2) the crown relief were less developed, which gave a blunt and roundish appearance, 3) the mesial shoulder of the mandibular canine was relatively higher, 4) the cervical ridge was more developed. Odontmetrically, the whole canine size was the greatest in Gorilla gorilla, followed by Pongo pygmaeus, Pan troglodytes, and Pan paniscus was the smallest. Male canines were significantly larger than female canines in the basal crown size as well as crown height in both jaws, especially the distance from the cusp tip to the mesial shoulder (CMSD). On the other hand, the enamel bulge of cervical portion in females was, absolutely and relatively, significantly stronger. The canines in four species of the Great apes reveals a definite sexual dimorphism in size and shape, which may reflect social structure.

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Prehistoric Jomon hunter-gatherers are distinct from majority of the Iron Age Yayoi and later populations of Japan in showing distally elongated intra-limb proportion. Intra-limb proportion in modern humans is often linked to ecogeographic rule of Allen, and is considered to reflect local temperature. If this is correct, considerably large intra-limb proportion of Jomon suggests their adaptation to tropical climate, and contradicts with the fact that they had lived on the temperate/subarctic Japanese archipelago for more than 10000 years. However, the original Allen’s rule denotes size proportion between trunk and appendages, and this proportion better associates with climate in humans rather than intra-limb proportion. In this study, we investigate relative limb lengths compared to trunk size in Jomon, “immigrant” Yayoi, and early-modern Edo populations of Japan. The ratios of Jomon and Yayoi are similar to each other, and are comparable to those for temperate/subarctic populations of Europe. Therefore, the body shape of Jomon is not a tropical type in view of thermoregulation. This finding does not exclusively support but is at least consistent with the recent hypothesis that Jomon originated from a Paleolithic population inhabited in Northeast Asia. However, the low ratios found in the sample of short-statured Edo people suggest that intra-limb proportion is sometimes affected by environmental factors other than climate. On the other hand, principal component analyses based on bi-iliac breadth and limb bone lengths indicate significant differences in overall body form between Jomon and Yayoi, particularly in males. Such differences probably reflect different genealogical backgrounds of these two populations.

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[in Japanese]

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