大型類人猿4種の犬歯形態と性的二型  [in Japanese] Canine crown morphology and sexual dimorphism in the Great apes  [in Japanese]

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Abstract

大型類人猿における犬歯形態と性的二型を明らかにすることを目的に研究を行った。資料は各博物館・研究所に所蔵されている大型類人猿(オランウータン,ゴリラ,チンパンジー,ボノボ)の頭蓋骨に植立している犬歯の超硬石膏模型である。大型類人猿の犬歯の歯冠サイズはオスが大きく,メスは小さい。舌側面からみた歯冠概形は4種とも上顎がオスで底辺の広い二等辺三角形,メスで正三角形を,下顎は雌雄とも不正四辺形を呈す。雌雄とも近心shoulderの位置は上顎のほうが下顎よりも歯頸寄りに,また浮彫像では上顎犬歯で近心半部に近心舌側隆線が,下顎では遠心舌側へ遠心舌側面隆線が走行する。4種で比較すると,オランウータンはオスで歯表面に皺が多いこと,また歯冠と歯根がスムーズに移行し,歯頸部にくびれがないことが特徴的である。ゴリラではオスの上顎犬歯の歯頸隆線の発達が弱いこと,および下顎犬歯の近心舌側面窩にある切痕が強いことが特徴であり,<i>Pan</i>属の2種で雌雄とも上顎犬歯の遠心shoulderが近心shoulderの位置と同等か,それより尖頭寄りにあること,ボノボでは雌雄とも上顎犬歯の遠心舌側面隆線が歯頸隆線と合流してL字状の形態を呈すことが特徴的である。大型類人猿4種では犬歯の性差は大きさだけでなく,歯の形態や歯冠構造でも明らかである。メスの犬歯は以下の特徴でそれぞれの種のオスの犬歯と違いがみられた:1)全体的に小さい,2)表面の浮彫は発達が弱く,全体的に丸みを帯びた形態をしている,3)下顎犬歯の近心shoulderは相対的に尖頭寄りにある,4)歯頸隆線は発達が良い。歯冠の計測値ではゴリラが最も大きく,次いでオランウータン,チンパンジーが続き,ボノボが最も小さい。オスの方が歯冠高を含め歯冠サイズは大きい。とくに尖頭と近心shoulder間距離が最も性差が強い。一方,歯頸部エナメル質の膨らみ具合はメスの方が絶対的にも相対的にも値が高い。類人猿の社会構造との比較では,単独生活者のオランウータンと単雄複雌群のゴリラは強い性的二型を,複雄複雌群のチンパンジーやボノボではサイズはこれよりもやゝ弱い性的二型が認められた。

This paper described crown morphology and sexual dimorphism of the canines in four species of the Great apes; <i>Pongo pygmaeus</i>, <i>Gorilla gorilla</i>, <i>Pan trogrodytes</i>, and <i>Pan paniscus</i>. 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, <i>Pongo pygmaeus</i> was characterized by wrinkles on crown surface and a smooth transition between crown and root in males. In <i>Gorilla gorilla</i>, 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 <i>Pan</i>, 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 <i>Pan paniscus</i> 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 <i>Gorilla gorilla</i>, followed by <i>Pongo pygmaeus</i>, <i>Pan troglodytes</i>, and <i>Pan paniscus </i>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.

Journal

  • Anthropological Science (Japanese Series)

    Anthropological Science (Japanese Series) 123(2), 93-109, 2015

    The Anthropological Society of Nippon

Codes

  • NII Article ID (NAID)
    130005113975
  • NII NACSIS-CAT ID (NCID)
    AA11307827
  • Text Lang
    JPN
  • ISSN
    1344-3992
  • NDL Article ID
    027046814
  • NDL Call No.
    Z19-11
  • Data Source
    NDL  J-STAGE 
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