Craniofacial Biomechanics of Primates

最近有新的兴趣，在确定的功能和适应意义的联合融合的灵长类动物和其他哺乳动物的下颌骨。 这种兴趣的一部分是因为联合融合被认为在哺乳动物，特别是灵长类动物evolution.This研究测试的假设，下颌肌肉力量招聘和发射模式不同物种的strepsirrhines，根据刚度和强度的联合发挥了重要作用。 这一假说预测，那些链鼻类物种，如indriids，具有更硬，更强，并且通常部分融合的联合，具有类似于在活的japonids中发现的衍生条件的下颌肌肉放电模式，即，“wishboning”模式。 此外，这一假说还预测，那些具有完全不融合和高度移动的联合的链鼻猴，如环尾狐猴和厚尾加拉戈斯，不具有这种模式。 相反，它们具有原始哺乳动物的运动模式，这在北美负鼠和树鼩中也有发现。这一假设将通过使用EMG技术分析环尾狐猴的咬肌、内侧翼肌和颞肌的肌力募集和放电模式来验证。（2）温和或竹狐猴（Hapalemur griseus），（3）狐猴（Propithecus verreauxi），和（4）狐猴（Dauplonia madagascariensis）。 据预测，环尾狐猴和aye-ayes的肌电图模式将更类似于厚尾加拉戈斯发现的模式，竹狐猴和狐猴的肌电图模式将更类似于那些模式中发现的狐猴。如果对竹狐猴和狐猴的预测得到证实，这就构成了对关于联合融合的个体发育时间假说的反驳，因为链鼻猴表现出晚期部分和/或完全融合的假设是没有“wishboning”模式的狐猴。 此外，这些数据还表明，“叉骨”模式的灵长类动物进化不止一次，如果是这样的话，也许它独立地在不同的灵长类动物谱系中进化了几次。 总之，本项目的主要目的是通过分析各种链鼻动物的下颌肌肉力量招募和放电模式来进一步研究这些问题，这些动物具有完全或部分未融合的联合，但联合刚度和强度不同

Recently there has been renewed interest in determining the functional and adaptive significance of symphyseal fusion of the mandible in primates and other mammals. This interest is in part because symphyseal fusion is thought to play an important role in various adaptive scenarios of mammalian and especially primate evolution.This study tests the hypothesis that jaw muscle force recruitment and firing patterns vary between species of strepsirrhines, depending on the stiffness and strength of their symphyses. This hypothesis predicts that those strepsirrhine species such as the indriids, with their stiffer, stronger, and often partially-fused symphyses, have a jaw-muscle firing pattern that is similar to the derived condition found in living anthropoids, i.e., the "wishboning" pattern. Furthermore, this hypothesis also predicts that those strepsirrhines with a completely unfused and highly mobile symphysis, such as ring-tailed lemurs and thick-tailed galagos, do not have this pattern. Instead, they have the primitive mammalian motor pattern, which is also found in North American opossums and tree shrews.This hypothesis will be tested by analyzing masseter, medial pterygoid and temporalis muscle force recruitment and firing patterns using EMG techniques in (1) ring-tailed lemurs (Lemur catta), (2) gentle or bamboo lemurs (Hapalemur griseus), (3) sifakas (Propithecus verreauxi), and (4) aye-ayes (Daubentonia madagascariensis). It is predicted that EMG patterns in ring-tailed lemurs and aye-ayes will be more similar to patterns found in thick-tailed galagos, and that EMG patterns in bamboo lemurs and sifakas will be more similar to those patterns found in anthropoids. If the predictions for bamboo lemurs and sifakas are confirmed, this constitutes a refutation of the ontogenetic timing hypothesis regarding symphyseal fusion simply because strepsirrhines that exhibit late partial and/or complete fusion are hypothesized to not have the "wishboning" pattern of anthropoids. Furthermore, these data would also indicate that the "wishboning" pattern of anthropoids evolved more than once within primates, and if so, perhaps it evolved independently several times in various primate lineages. In summary, the main purpose of this project is to pursue these matters further by analyzing jaw-muscle force recruitment and firing patterns in various strepsirrhine species that have completely or partially unfused symphyses, but yet vary in the amount of symphyseal stiffness and strength