Craniofacial Biomechanics of Primates

最近，人们对确定灵长类动物和其他哺乳动物下颌骨联合融合的功能和适应性意义重新产生了兴趣。这种兴趣的部分原因是，联合骨融合被认为在哺乳动物尤其是灵长类动物进化的各种适应情景中起着重要作用。这项研究验证了一个假设，即不同种类的链霉菌的颚肌力量募集和发射模式是不同的，这取决于它们联合的刚度和强度。这一假说预测，那些链球菌属的物种，如印度河人，有着更硬、更强壮、经常部分融合的联合，有一种颌肌发射模式，类似于在现存的类人猿身上发现的衍生条件，即“许愿”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联合的链霉素，如环尾狐猴和厚尾加拉戈斯，没有这种模式。相反，它们具有原始哺乳动物的运动模式，这种模式在北美负鼠和树鼩身上也有发现。这一假设将通过使用肌电图技术分析咬肌、内侧翼状肌和颞肌的力量恢复和放电模式来验证(1)环尾狐猴（Lemur catta），(2)温柔或竹狐猴（Hapalemur griseus），(3)狐猴（Propithecus verreauxi）和(4)眼猴（Daubentonia madagascar）。预计环尾狐猴和眼尾狐猴的肌电信号模式将与厚尾加拉戈斯的肌电信号模式更为相似，竹尾狐猴和狐猴的肌电信号模式将与类人猿的肌电信号模式更为相似。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生时间假说的反驳，因为表现出部分和/或完全融合的链霉菌被假设为没有类人猿的“许愿”模式。此外，这些数据还表明，类人猿的“许愿”模式在灵长类动物中不止一次进化，如果是这样的话，也许它在不同的灵长类动物谱系中独立进化了好几次。综上所述，本项目的主要目的是通过分析具有完全或部分不融合联合，但在联合刚度和强度上存在差异的各种链球菌物种的颚肌力量募集和发射模式来进一步研究这些问题

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