Terhune Claire E, Hylander William L, Vinyard Christopher J, Taylor Andrea B
Department of Orthopaedic Surgery, Duke University School of Medicine, Durham, NC, USA; Department of Anthropology, University of Arkansas, Fayetteville, AR, USA.
Department of Evolutionary Anthropology, Duke University, Durham, NC, USA.
J Hum Evol. 2015 May;82:145-58. doi: 10.1016/j.jhevol.2015.02.006. Epub 2015 Apr 7.
Maximum jaw gape is a performance variable related to feeding and non-feeding oral behaviors, such as canine gape displays, and is influenced by several factors including jaw-muscle fiber architecture, muscle position on the skull, and jaw morphology. Maximum gape, jaw length, and canine height are strongly correlated across catarrhine primates, but relationships between gape and other aspects of masticatory apparatus morphology are less clear. We examine the effects of jaw-adductor fiber architecture, jaw-muscle leverage, and jaw form on gape in an intraspecific sample of sexually dimorphic crab-eating macaques (Macaca fascicularis). As M. fascicularis males have relatively larger maximum gapes than females, we predict that males will have muscle and jaw morphologies that facilitate large gape, but these morphologies may come at some expense to bite force. Male crab-eating macaques have relatively longer jaw-muscle fibers, masseters with decreased leverage, and temporomandibular joint morphologies that facilitate the production of wide gapes. Because relative canine height is correlated with maximum gape in catarrhines, and males have relatively longer canines than females, these results support the hypothesis that male M. fascicularis have experienced selection to increase maximum gape. The sexes do not differ in relative masseter physiologic cross-sectional area (PCSA), but males compensate for a potential trade-off between muscle excursion versus muscle force with increased temporalis weight and PCSA. This musculoskeletal configuration is likely functionally significant for behaviors involving aggressive canine biting and displays in male M. fascicularis and provides additional evidence supporting the multifactorial nature of the catarrhine masticatory apparatus. Our results have implications for the evolution of craniofacial morphology in catarrhine primates and reinforce the importance of evaluating additional factors other than feeding behavior and diet in analyses of masticatory apparatus form, function, and evolution.
最大张口度是一个与进食及非进食口腔行为（如犬齿张开展示）相关的表现变量，并且受到多种因素影响，包括颌肌纤维结构、肌肉在颅骨上的位置以及颌骨形态。在狭鼻猴类灵长动物中，最大张口度、颌骨长度和犬齿高度密切相关，但张口度与咀嚼器官形态其他方面之间的关系尚不清楚。我们在食蟹猕猴（Macaca fascicularis）这个具有性别二态性的种内样本中，研究了颌内收肌纤维结构、颌肌杠杆作用和颌骨形态对张口度的影响。由于雄性食蟹猕猴的最大张口度相对大于雌性，我们预测雄性会具有有助于张大嘴巴的肌肉和颌骨形态，但这些形态可能会在一定程度上牺牲咬合力。雄性食蟹猕猴具有相对较长的颌肌纤维、杠杆作用降低的咬肌，以及有助于张大嘴巴的颞下颌关节形态。因为在狭鼻猴中，相对犬齿高度与最大张口度相关，且雄性的犬齿相对比雌性更长，这些结果支持了雄性食蟹猕猴经历了增加最大张口度的选择这一假设。两性在相对咬肌生理横截面积（PCSA）上没有差异，但雄性通过增加颞肌重量和PCSA来弥补肌肉行程与肌肉力量之间的潜在权衡。这种肌肉骨骼结构对于雄性食蟹猕猴涉及攻击性犬齿撕咬和展示的行为可能具有重要功能意义，并提供了额外证据支持狭鼻猴咀嚼器官的多因素性质。我们的结果对狭鼻猴类灵长动物颅面形态的进化具有启示意义，并强化了在咀嚼器官形态、功能和进化分析中评估除进食行为和饮食之外的其他因素的重要性。
