Doctoral Dissertation Research: Skull Growth and Biomechanical Constraints on Molar Emergence in Primates

人类的生活史在现存的灵长类动物中是独一无二的。人类生长缓慢，寿命长，再加上出生间隔短，导致繁殖率很快。在灵长类动物中，生活史与第一颗恒磨牙出现在口腔中的年龄之间存在着密切的关系。古人类学家利用这种关系来探索独特的人类生活史的古老轮廓，但究竟为什么磨牙的出现会发生变化，并与生活史密切相关，目前尚不清楚。这项研究将研究磨牙出现作为一个发展中的，功能集成的咀嚼系统的一部分，为灵长类动物中磨牙出现时间的背景变化提供一个模型。这也将有助于理解磨牙出现和生活史之间的密切联系。该项目将产生一个丰富的3D灵长类头骨生长的公共数据库，与颅面生长和磨牙阻生的研究相关，并支持STEM领域的公共科学推广和研究生和本科生的培训。磨牙与下巴和咀嚼肌肉一起工作，分解食物。咀嚼系统这些部分之间的发育协调对一生的食物摄取至关重要。在成年灵长类动物中，咀嚼系统的配置限制了磨牙的位置，以避免在咀嚼过程中对颞颌关节造成损害。使用来自灵长类头骨(n=18个物种；1,182个标本)横断面个体发育样本的3D坐标数据，本研究将确定磨牙出现的位置是否以同样的方式受到限制，从而调节磨牙出现的时间。这项研究将研究咀嚼系统结构的个体发育变化如何驱动灵长类动物磨牙出现时间的变化，并可能表明生活史通过影响面部生长速度与磨牙出现年龄密切相关。这将进一步表明，在导致人类的谱系中，选择较短的脸和较长的生长时间表将会伴随着推迟磨牙出现的效果。

Human life history is unique among living primates. Humans grow slowly and have long lifespans coupled with short inter-birth intervals, resulting in fast reproductive rates. Among primates, there is a strong relationship between life history and the age at which the first permanent molar emerges into the mouth. Paleoanthropologists use this relationship to probe the antiquity of the unique human life history profile, but exactly why molar emergence varies and is closely associated with life history remains unclear. This study will examine molar emergence as part of a developing, functionally integrated chewing system, to provide a model for contextualizing variation in the timing of molar emergence among primates. It will also contribute to understanding the close association between molar emergence and life history. The project will yield a rich public database of 3D primate skull growth with relevance to the study of craniofacial growth and molar impaction, and support public science outreach and training of graduate and undergraduate students in a STEM field. Molars function with the jaws and chewing muscles to break down food. Developmental coordination among these parts of the chewing system is critical for food ingestion throughout life. In adult primates, the configuration of the chewing system constrains the position of molars to avoid damage to the temporomandibular joint during chewing. Using 3D coordinate data from cross-sectional ontogenetic samples of primate skulls (n = 18 species; 1,182 specimens) this study will determine if the position of molar emergence is constrained in the same manner, thereby regulating the timing of molar emergence. This research will examine how ontogenetic changes in the configuration of the chewing system drive variation in molar emergence schedules among primates, and may suggest that life history is closely associated with molar emergence ages through its influence on facial growth rates. It will further suggest that selection for shorter faces and a prolonged growth schedule in the lineage leading to humans would have had the concomitant effect of delaying molar emergence.