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，再加上生育间隔短，导致繁殖速度快。在灵长类动物中，生命史与第一颗恒磨牙长出口腔的年龄有着密切的关系。古人类学家利用这种关系来探索独特的人类生活史轮廓的古代，但究竟为什么臼齿的出现是不同的，并且与生活史密切相关，仍然不清楚。本研究将研究磨牙出现作为发育的一部分，功能整合咀嚼系统，为灵长类动物磨牙出现时间的背景变化提供模型。这也将有助于理解磨牙的出现与生活史之间的密切联系。该项目将产生丰富的3D灵长类颅骨生长的公共数据库，与颅面生长和磨牙嵌塞的研究相关，并支持STEM领域的公共科学推广和研究生和本科生的培训。磨牙与颌骨和咀嚼肌肉一起工作，分解食物。咀嚼系统的这些部分之间的发育协调对整个生命的食物摄取至关重要。在成年灵长类动物中，咀嚼系统的结构限制了磨牙的位置，以避免在咀嚼时损伤颞下颌关节。利用灵长类动物颅骨横断面个体发生样本（n = 18种，1182个标本）的三维坐标数据，本研究将确定臼齿出牙的位置是否以同样的方式受到约束，从而调节臼齿出牙的时间。本研究将探讨咀嚼系统结构的个体发生变化如何驱动灵长类动物磨牙出现时间表的变化，并可能表明生活史通过其对面部生长速度的影响与磨牙出现年龄密切相关。这将进一步表明，在进化为人类的谱系中，选择较短的脸和较长的生长时间表，可能会导致臼齿出现时间的推迟。

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.