Canine crown morphology and sexual dimorphism in the <i>Pan paniscus</i>

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  • ボノボの犬歯形態と性的二型
  • ボノボ ノ ケンシ ケイタイ ト セイテキ ニガタ

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Abstract

Canine morphology has been regarded as being too simple to be used in phylogenetic analysis. However, the canine tooth appears to include some important morphological traits. In the present study, we describe crown morphology and canine variation between and among sexes of the Pan paniscus. The results indicate that sexual dimorphism is significant, not only in the size but also in the shape and structure of the canine tooth. In males, the crowns of the maxillary and mandibular canines were much larger than in females. In the maxillary canine, we made several observations: 1) The contour of the crown from the lingual aspect in males was an equilateral triangle with long mesial and distal incisal crests, while in females it was an isosceles triangle with short incisal crests. 2) The mesial shoulder was situated lower, one-fifth of the crown height from the deepest cervical line in males vs. one-third in females. 3) The lingual cervical line was slightly curved or straight. 4) The mesial incisal groove was fairly developed. 5) The central groove ran from the cusp tip to the cervical line. 6) The developed distal lingual ridge was connected with the distal cervical ridge, which gave the appearance of an “L” shape. In the mandibular canine, the following observations were made: 1) The mesial shoulder was ranged from one-third to two-thirds of the crown height from the deepest cervical line in both sexes. 2) The angle between the mesial crest and the mesial marginal ridge was about 110 degrees in males. 3) The main ridge (distal lingual ridge) in males was developed more than in females. 4) The distal lingual tubercle was more prominent in males than in females. 5) The cervical ridge swelled out in the lower portion of the crown base in males vs. the upper portion in females. 6) The distal lingual groove was deeper and “U” shaped at the bottom in both sexes. As a whole, surface relief features, such as grooves and ridges, were less developed in females than in males, which gave a roundish appearance to the female canine. Compared with other hominoids, the Pan paniscus canine revealed a definite sexual dimorphism in size, shape and structure, which may reflect an intimate social structure of the multi-male unit. The differences in the canine morphology between Pan paniscus and Homo sapiens were numerous not only in size but also in shape and structure.<br>

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