Functional Analysis of the Skull in South American Capuchin Monkeys

本研究通过对成年黑帽卷尾猴眶间、身体和下颌骨联合的测量器进行活体分析，对其在剧烈咬咬和咀嚼坚硬食物时的骨张力进行分析，将直接评估高等灵长类动物眼眶周围区域和下颌联合的功能形态，因为它与咀嚼复合体有关。卷尾猴与其他灵长类动物不同，它们经常使用门牙和臼齿来处理坚硬的食物。本研究旨在探讨在同一动物中，在门牙强力咬合和咀嚼期间，对联合肌和眉脊形式的负荷制度的相对影响。关于颅形和功能的两种假设将被测试：高等灵长类动物的联合骨融合与大量使用门牙时所经历的压力有关，尼安德特人和其他类人猿的眉脊形成是由于更大的门牙负荷。如果在有力的切牙咬合和咬合过程中，联合处的最大应变水平明显更高，那么就有可能将垂直切牙和切牙负荷与高等灵长类动物联合融合的进化联系起来。在评估切牙负荷对眉骨形成的相对影响时，下颌和眶间应变水平将与颅应变梯度测试进行比较。对于被认为是一种消除咀嚼应力的功能适应的环眶结构，不应观察到眶间和下颌应变水平之间的差异。或者，应变梯度的存在表明加载制度对眉脊形成的次要影响。在这种情况下，环眼眶形状的遗传和表观遗传控制将被视为相对独立于影响下颌形状的因素。这也支持了沿上面部的骨骼保护特殊感觉器官免受创伤的说法。

Using an in vivo analysis of bone strain during vigorous biting and chewing of tough foods from gages affixed to the interorbit, body, and symphysis of the mandible in adult black-capped capuchin monkeys, this research will directly evaluate the functional morphology of the area around the eye orbit and mandibular symphysis in higher primates as it relates to the masticatory complex. Capuchins, unlike many other primates, often use the incisors as well as molars to process tough foods. This study is designed to investigate the relative effects on symphyseal and browridge form of loading regimes during forceful biting with the incisors and during chewing in the same animal. Two hypotheses regarding cranial form and function will be tested: symphyseal fusion in higher primates is linked to stresses experienced during heavy use of the incisors, and browridge formation in neandertals and other hominoids is due to greater incisal loading. If maximal strain levels at the symphysis are significantly higher during powerful incisor biting and clenching, then it will be possible to link vertical incisors and incisal loading to the evolution of symphyseal fusion in higher primates. In assessing the relative influence of incisor loading on browridge formation, mandibular and interorbital strain levels will be compared to test for a cranial strain gradient. For a circumorbital structure to be considered a functional adaptation to dissipate masicatory stress, no difference should be observed between interorbital and mandibular strain levels. Alternatively, the presence of a strain gradient would suggest a secondary effect of a loading regime on browridge formation. In this case, genetic and epigenetic controls of circumorbital form would be viewed as relatively independent of factors affecting jaw form. This would also support the claim that bone along the upper face serves to protect the special sense organs from traumatic forces.