Craniofacial Biomechanics of Primates

最近，人们对确定灵长类和其他哺乳动物下颌骨联合融合的功能和适应意义重新产生了兴趣。这种兴趣在一定程度上是因为联合融合被认为在哺乳动物特别是灵长类进化的各种适应情景中发挥着重要作用。这项研究检验了一种假说，即颌部肌肉力量招募和发射模式在链状动物物种之间存在差异，这取决于它们联合的硬度和强度。这一假说预测，那些链鼻目动物物种，如粘虫，具有更坚硬、更强壮且往往部分融合的联合体，具有类似于在现生类人猿中发现的衍生条件的颌肌放电模式，即“愿望骨”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性的联合体的链猴，如环尾狐猴和厚尾Galagos，没有这种模式。相反，它们拥有原始哺乳动物的运动模式，这也在北美负鼠和树懒中发现。这一假设将通过分析咬肌、内侧翼猴和颞肌的力量招募和发射模式来验证，方法是使用肌电技术在(1)环尾狐猴(狐猴)、(2)温和或竹子狐猴(Hapalemur Griseus)、(3)sifakas(Propithecus Verreauxi)和(4)ae-ayes(Daubentonia Madagascariensis)中进行验证。据预测，环尾狐猴和野猴的肌电模式将更类似于厚尾Galago的模式，竹狐猴和西法卡的肌电模式将更类似于类人猿的模式。如果竹狐猴和西法卡的预测得到证实，这就构成了对关于联合融合的个体发育计时假说的反驳，因为表现出晚期部分和/或完全融合的链状狐猴被假设没有类人猿的“愿望骨”模式。此外，这些数据还表明，类人猿的“愿望骨”模式在灵长类动物中进化了不止一次，如果是这样的话，它可能在不同的灵长类动物谱系中独立进化了几次。总而言之，这个项目的主要目的是通过分析各种链鼻鱼物种的颌肌力招募和发射模式来进一步探讨这些问题，这些物种具有完全或部分未融合的联合，但联合的僵硬和强度的数量却不同。

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