Symphyseal Placsticity Properties and Performance in Primate and Non-Primate Mammals

研究骨骼功能的生物人类学家通常从骨骼的大小和形状来推断行为和表现。这种近似已经形成了灵长类动物骨骼与它们的生长和生活方式之间关系的基本概念。然而，当检查形状怪异、生长模式不同或组织组成不同的结构时，从骨骼形状估计性能变得困难。灵长类动物的下颌联合就是这样一个关节，无法用简单的模型来描述它的表现。联合骨节解剖学的范围从原始哺乳动物的光滑、相对的左右颌骨，由纤维组织、纤维软骨和一些韧带松散连接，到紧密结合的关节，其缝合线更复杂，由互锁的骨皱襞和许多钙化的韧带组成，再到人类和各种其他灵长类动物的更独特的骨化关节。人们对这种显著变化的行为和力学相关性知之甚少。事实上，如果不能把节骨节的形式与关节的完整性联系起来，就会削弱我们对灵长类动物化石摄食器官的功能和进化以及行为重建的认识。第一个目标是量化灵长类动物和非灵长类哺乳动物在模拟加载期间的联合强度。关节性能的测量将与关节比例、生物矿化和内部解剖的数据相结合。第二个目标是检查联合组织的可塑性和特性。为了获得关节负荷的变化，基因相似的兔子将在不同浓度的食物上饲养。通过量化物种内和物种间的关节完整性，本实验研究将关节形状与抗载荷特性和性能联系起来，解决了涉及联合的主要问题，并为未来关节功能的研究提供了模型。这项研究的一个更广泛的影响是它扩展了生物人类学家和工程师之间正在进行的多学科合作关系。它的教育价值在于，学生和教师，特别是代表性不足的群体，将通过长期的学徒制、跨学科培训和推广受益。对社会的好处包括为未来的关节负荷、组织反应和性能的进化和临床项目提供关键的基础数据。

Bioanthropologists studying skeletal function typically infer behavior and performance from bony size and shape. This approximation has fostered a basic notion of how primate skeletons relate to their growth and lifestyles. However, estimating performance from skeletal shape becomes difficult when one examines structures that are oddly-shaped, differ in growth patterns, or vary in tissue composition. The primate mandibular symphysis is one such joint that defies simplistic modeling of its performance. Symphyseal anatomy ranges from the primitive mammalian condition of smooth, opposing right and left jaws loosely connected by fibrous tissue, fibrocartilage and some ligaments to a tightly bound joint with greater sutural complexity consisting of interlocking bony rugosities and numerous calcified ligaments to the more unique condition of an ossified joint seen in humans and various other primates. The behavioral and mechanical correlates of this remarkable variation are poorly understood. Indeed, failure to relate symphyseal form to joint integrity undermines our knowledge of the function and evolution of the feeding apparatus and behavioral reconstructions of fossil primates. The first objective is to quantify symphyseal strength during simulated loading regimes in primate and non-primate mammals. Measures of joint performance will be integrated with data on joint proportions, biomineralization and internal anatomy. The second goal is to examine the plasticity and properties of symphyseal tissues. To obtain variation in joint loads, cohorts of genetically similar rabbits will be raised on foods of different consistencies. By quantifying joint integrity within and across species, this experimental study links load-resisting properties and performance to joint shape, addresses major issues involving the symphysis, and serves as a model for future work on joint function. A broader impact of this study is its expansion of an ongoing multidisciplinary partnership between bioanthropologists and engineers. Its educational merit is that students and teachers, especially under-represented groups, will benefit via long-term apprenticeship, interdisciplinary training, and outreach. The benefit to society includes providing key basic data for future evolutionary and clinical projects on joint loading, tissue responses, and performance.