Sexual dimorphism has been widely documented in primates, however craniodental sexual dimorphism among hylobatids has not been well researched. In this study, I investigate interspecific differences in the presence and pattern of craniodental sexual dimorphism among gibbons and siamang using data taken from eight species representing all four hylobatid genera (Hoolock leuconedys, Hylobates agilis, Hy. klossi, Hy. lar, Hy. muelleri, Hy. pileatus, Nomascus gabriellae, and Symphalangus syndactylus). I sampled 17-30 cranial specimens for each species. I quantified craniofacial and upper canine crown height dimorphism using morphometric data taken from 3D surface models and directly from dry specimens to examine the presence and pattern of craniodental sexual dimorphism among hylobatids. Hoolock leuconedys shows statistically significant sex differences across all craniofacial shape and form measures investigated. Although Hy. lar, Ho. leuconedys, and S. syndactylus all show statistically significant cranial form dimorphism, there are interspecific differences in how this dimorphism is expressed. Hoolock leuconedys, Hy. lar, and S. syndactylus are unique in showing upper canine crown height dimorphism, and Ho. leuconedys show a high level of browridge dimorphism in which white fur highlights this region in males, in contrast to their black body and facial pelage. The finding of male-biased sexual dimorphism in only some hylobatid taxa suggests that although male craniofacial morphology of some gibbon and siamang species may be associated with sex-specific agonistic interactions, this effect is not ubiquitous among hylobatids. Further research is required to understand these findings in the context of the socioecology of individual hylobatid taxa.

灵长类动物的性二态性已被广泛记录，但长尾猿的颅牙性二态性尚未得到很好的研究。在这项研究中，我使用来自代表所有四个长臂猿属（Hoolock leuconedys、Hylobates agilis、Hy. klossi、Hy. lar、Hy. muelleri）的八个物种的数据调查了长臂猿和长臂猿之间颅牙两性异形的存在和模式的种间差异, Hy.pileatus , Nomascus gabriellae和Symphalangus syndactylus）。我为每个物种采集了 17-30 个颅骨标本。我使用从 3D 表面模型和直接从干标本中获取的形态测量数据量化了颅面和上犬牙冠高度二态性，以检查长尾猿之间颅牙性二态性的存在和模式。Hoolock leuconedys在所有被调查的颅面形状和形态测量中显示出统计学上显着的性别差异。虽然海。拉，何。leuconedys和S. syndactylus都显示出统计学上显着的颅型二态性，这种二态性的表达方式存在种间差异。Hoolock leuconedys，Hy。lar和S. syndactylus在显示上犬牙冠高度二形性方面是独一无二的，Ho。leuconedys表现出高度的眉脊二态性，其中白色皮毛突出了雄性的这一区域，与黑色的身体和面部皮毛形成鲜明对比。仅在一些长臂猿类群中发现雄性偏向的性别二态性表明，虽然一些长臂猿和长臂猿物种的雄性颅面形态可能与性别特异性激动相互作用有关，但这种影响在长臂猿中并不普遍。需要进一步研究以在个体长尾猿类群的社会生态学背景下理解这些发现。