Abstract
We aimed to describe crown morphology and sexual dimorphism of the canine in the Hylobates lar. As have been reported in the previous studies, the canines of male and female Hylobates lar were nearly the same in morphology as well as in size. Viewed from the buccal aspect, the contours of maxillary canines of both sexes had a saber-like form, while those of the mandibular canines had a quadrilateral form. However, the results in the present study indicated that sexual dimorphism in the canines of Hylobates lar was slightly but definitely found, not only in the size but also in the shape and structure of the canine teeth. Compared with the male canines, the female canines were characterized as follows: 1) smaller in whole size, 2) the crown reliefs, such as grooves and ridges, were less developed, which gave blunt and roundish appearance, 3) the mesial shoulder of mandibular canine was located relatively higher toward the cusp tip, 4) the cervical ridge was more developed. Odontmetrically, male canines were significantly larger in the basal crown size and higher in crown height. Crown heights in upper and lower jaws, especially the distance from the cusp tip to the mesial shoulder were also greater in males than females. On the other hand, the enamel bulge of cervical portion relative to maximum diameter of the mandibular canine crown was significantly stronger in female. Moreover, the mesial shoulder in female located as high as middle of the crown height; the average relative distance between mesial shoulder and cervical line in male was 32.8% of the crown height, while 48.1% in female. The degree of canine sexual dimorphism in Hylobates suggests that sexual differences are present even in the paired-social group, which may suggest male male competition in Hylobates lar.
