Doctoral Dissertation Improvement: Temporomandibular Joint Variation in Anthropoid Primates: Inferences from Phylogeny, Function, and Allometry

体质人类学的两个主要目标是重建现存和灭绝类群之间的系统发育关系，并调查形态对饮食的适应。颞下颌关节（TMJ），作为咀嚼器官的关键部分，并作为唯一的点，下颌骨直接接触颅骨，有可能提供有关饮食适应的信息。此外，由于TMJ上和周围的字符经常用于系统发育分析，了解这种形态的变化是至关重要的，了解类群之间的关系。然而，目前很少有数据是关于颞下颌关节在灵长类动物中的变化;此外，这种结构的变化如何反映进化关系或咀嚼功能的差异尚不清楚。为了解决这种缺乏数据的问题，本项目将通过测试一系列假设来评估TMJ的系统发育和功能意义，这些假设旨在研究一系列可能影响TMJ形状的因素，包括发育、饮食和与大小相关的分类群之间的形状差异。这些假设将使用头骨的三维地标数据和几何形态测量学进行测试，这是一种强大的定量方法，可以总结和比较个体和群体之间的形状差异。这种方法是特别有用的量化的颞下颌关节，其复杂性阻碍了以前的分析。将收集广泛的灵长类物种的数据。将检查灵长类动物颞下颌关节形状和分子关系之间的一致性，将通过具有不同饮食的密切相关物种之间的多个成对比较来评估与饮食差异相关的颞下颌关节变化，并将使用遗传学上广泛的种间方法对体型影响进行分析。这项研究将包括对颅骨解剖学中一个知之甚少的区域进行量化，该区域经常用于化石和活灵长类动物的研究;因此，这项研究有几个好处。首先，这种方法可以揭示重要的差异，TMJ形状之间的类群，以前没有被确定。其次，将这种变异与已知的进化、饮食或分类群之间的大小差异联系起来，将为未来的研究人员提供有关该区域功能和进化意义的详细知识，这对于理解人类和灵长类动物颅骨形状的进化至关重要。这项研究也将对解释灭绝灵长类动物的进化历史和饮食适应产生影响，因为它将有助于描述灵长类动物变异的三维数据集的不断增长。最后，拟议的研究可能有重要意义的临床分析的骨反应的颞下颌关节功能障碍相关的治疗。

Two major goals in physical anthropology are reconstructing phylogenetic relationships among living and extinct taxa and investigating morphological adaptations to diet. The temporomandibular joint (TMJ), as a critical portion of the masticatory apparatus and as the only point at which the mandible directly contacts the cranium, has the potential to provide information regarding dietary adaptations. Furthermore, since characters on and around the TMJ are frequently used in phylogenetic analyses, understanding variation in this morphology is crucial for understanding relationships among taxa. However, few data are currently available regarding how the TMJ varies within primates; furthermore, how variation in this structure reflects differences in evolutionary relationships or masticatory function is unclear. To address this lack of data, this project will assess the phylogenetic and functional significance of the TMJ by testing a series of hypotheses designed to examine a range of factors that may govern TMJ shape, including phylogeny, diet, and size related shape differences among taxa. These hypotheses will be tested using three-dimensional landmark data of the skull and geometric morphometrics, a powerful quantitative method by which differences in shape among individuals and groups can be summarized and compared. This methodology is particularly useful for quantification of the TMJ, the complexity of which has hindered previous analyses. Data will be collected for a wide cross-section of primate species. The congruence between TMJ shape and molecular relationships in primates will be examined, TMJ variation in relation to dietary differences will be assessed via multiple pairwise comparisons between closely related species with distinct diets, and analyses of the influence of body size will be conducted using a phylogenetically broad, interspecific approach. This study will include the quantification of a poorly understood region of cranial anatomy that is frequently used in studies of fossil and living primates; as a result, there are several benefits to this research. First, this approach can reveal important differences in TMJ shape among taxa that have previously been unidentified. Second, linking this variation to known evolutionary, dietary, or size differences between taxa will provide future researchers with detailed knowledge regarding the functional and evolutionary significance of this region, which is crucial for understanding the evolution of human and primate cranial shape. This research will also have implications for interpreting the evolutionary history and dietary adaptations of extinct primates, because it will contribute to the growing set of three-dimensional data describing primate variation. Finally, the proposed research may have important implications for clinical analyses of the bony response of the TMJ to treatments associated with TMJ dysfunction.