Max Planck Weizmann Center for Integrative Archaeology and Anthropology Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
Centre for Anatomical and Human Sciences Hull York Medical School, York, United Kingdom.
Am J Phys Anthropol. 2018 Oct;167(2):291-310. doi: 10.1002/ajpa.23628. Epub 2018 Aug 31.
Changes to soft- and hard-tissue components of the masticatory complex during development can impact functional performance by altering muscle excursion potential, maximum muscle forces, and the efficiency of force transfer to specific bitepoints. Within Macaca fascicularis, older individuals exploit larger, more mechanically resistant food items and more frequently utilize wide-gape jaw postures. We therefore predict that key architectural and biomechanical variables will scale during ontogeny to maximize bite force and gape potential within older, larger-bodied individuals.
We analyzed 26 specimens of M. fascicularis, representing a full developmental spectrum. The temporalis, superficial masseter, and deep masseter were dissected to determine muscle mass, fiber length, and physiologic cross-sectional area (PCSA). Lever-arm lengths were also measured for each muscle, alongside the height of the temporomandibular joint (TMJ) and basicranial length. These variables were scaled against two biomechanical variables (jaw length and condyle-molar length) to determine relative developmental changes within these parameters.
During ontogeny, muscle mass, fiber length, and PCSA scaled with positive allometry relative to jaw length and condyle-molar length within all muscles. TMJ height also scaled with positive allometry, while muscle lever arms scaled with isometry relative to jaw length and with positive allometry (temporalis) or isometry (superficial and deep masseter) relative to condyle-molar length.
Larger individuals demonstrate adaptations during development towards maximizing gape potential and bite force potential at both an anterior and posterior bitepoint. These data provide anatomical evidence to support field observations of dietary and behavioral differences between juvenile and adult M. fascicularis.
咀嚼复合体的软、硬组织结构在发育过程中的变化，可能通过改变肌肉的运动潜能、最大肌肉力以及力向特定咬合点传递的效率，从而影响功能表现。在猕猴属中，较年长的个体利用更大、更具机械抗性的食物，并更频繁地采用大张口姿势。因此，我们预测关键的结构和生物力学变量将在个体发育过程中进行缩放，以最大限度地提高年长、体型较大个体的咬合力和张口潜能。
我们分析了 26 只猕猴属标本，代表了完整的发育谱。颞肌、浅咬肌和深咬肌被解剖出来以确定肌肉质量、纤维长度和生理横截面积（PCSA）。还测量了每个肌肉的杠杆臂长度，以及颞下颌关节（TMJ）和颅底长度的高度。这些变量与两个生物力学变量（下颌长度和髁突-磨牙长度）进行了缩放，以确定这些参数内的相对发育变化。
在发育过程中，所有肌肉的肌肉质量、纤维长度和 PCSA 与下颌长度和髁突-磨牙长度呈正异速生长关系。TMJ 高度也呈正异速生长关系，而肌肉杠杆臂长度与下颌长度呈等距生长，与髁突-磨牙长度呈正异速生长（颞肌）或等距生长（浅咬肌和深咬肌）。
较大的个体在发育过程中表现出适应性，以最大限度地提高前牙和后牙咬合点的张口潜能和咬合力潜能。这些数据为猕猴属在幼年和成年个体之间饮食和行为差异的野外观察提供了解剖学证据。
