Evolutionary Anthropology Lab, Department of Anthropology, University of Minnesota, Minneapolis, Minnesota.
Department of Pathology and Anatomical Sciences, University of Missouri, Columbia, Missouri.
Am J Phys Anthropol. 2020 Oct;173(2):322-336. doi: 10.1002/ajpa.24048. Epub 2020 Mar 13.
Variation in primate masticatory form and function has been extensively researched through both morphological and experimental studies. As a result, symphyseal fusion in different primate clades has been linked to either the recruitment of vertically directed balancing-side muscle force, the timing and recruitment of transversely directed forces, or both. This study investigates the relationship between jaw muscle activity patterns and morphology in extant primates to make inferences about masticatory function in extinct primates, with implications for understanding the evolution of symphyseal fusion.
Three-dimensional mandibular landmark data were collected for 31 extant primates and nine fossil anthropoids and subfossil lemur species. Published electromyography (EMG) data were available for nine of the extant primate species. Partial least squares analysis and phylogenetic partial least squares analysis were used to identify relationships between EMG and jaw shape data and evaluate variation in jaw morphology.
Primates with partial and complete symphyseal fusion exhibit shape-function patterns associated with the wishboning motor pattern and loading regime, in contrast to shape-function patterns of primates with unfused jaws. All fossil primates examined (except Apidium) exhibit jaw morphologies suggestive of the wishboning motor pattern demonstrated in living anthropoids and indriids.
Partial fusion in Catopithecus, similar to indriids and some subfossil lemurs, may be sufficient to resist, or transfer, some amounts of transversely directed balancing-side muscle force at the symphysis, representing a transition to greater reliance on transverse jaw movement during mastication. Furthermore, possible functional convergences in physiological patterns during chewing (i.e., Archaeolemur) are identified.
通过形态学和实验研究，广泛研究了灵长类动物咀嚼的形式和功能的变化。因此，不同灵长类分支的联合融合与垂直定向的平衡侧肌肉力的募集、横向力的时机和募集或两者都有关。本研究调查了现生灵长类动物的颌骨肌肉活动模式与形态之间的关系，以便对已灭绝灵长类动物的咀嚼功能进行推断，从而有助于理解联合融合的进化。
为 31 种现存灵长类动物和 9 种化石类人猿和亚化石狐猴物种收集了三维下颌骨地标数据。发表的肌电图（EMG）数据可用于 9 种现存的灵长类动物物种。使用偏最小二乘法分析和系统发育偏最小二乘法分析来识别 EMG 和颌骨形状数据之间的关系，并评估颌骨形态的变化。
部分和完全联合融合的灵长类动物表现出与“wishboning”运动模式和加载模式相关的形状-功能模式，与未融合的颌骨的形状-功能模式形成对比。检查的所有化石灵长类动物（除了 Apidium）都表现出与现存类人猿和大狐猴中展示的“wishboning”运动模式相似的颌骨形态。
类似于大狐猴和一些亚化石狐猴的 Catopithecus 的部分融合可能足以抵抗或传递联合处的一些横向平衡侧肌肉力，代表在咀嚼过程中对横向颌运动的更大依赖的转变。此外，还确定了咀嚼过程中生理模式的可能功能趋同（即 Archaeolemur）。
