Collaborative Research: Integrative Investigation of the Evolution and Biomechanics of Mandibular Form in Hominids

关于人类起源的基本问题之一是我们的古人类祖先如何生活。这项研究使用了多学科的方法（古生物学，古生态学，比较解剖学，实验生物学）来询问有关灭绝的人类种群如何在自然景观中表现的问题。具体来说，研究人员将分析下颌骨（下颌骨），这是早期人类化石记录中最常见的骨骼部分，现代类人猿和两种早期灭绝的人类（南方古猿），以了解下颌骨的结构如何与进食行为和饮食的变化有关。这项研究将提供新的数据，说明饮食和喂养行为的变化如何随着时间的推移改变我们的解剖结构，从而更有力地解释我们成为人类的过程。更广泛的影响将包括对本科生、研究生和博士后进行化石分析最新分析技术方面的培训;利用旨在加强人类起源教学的实践经验和网络内容，向中小学科学教师和学生开展外联活动;以及制作一套独特的现代猿类和稀有化石标本的3D数据集，供科学界使用。下颌骨是人类化石记录中牙齿之后最常见的元素;它们被用来诊断物种，测试系统发育假说，推断进食行为和饮食。然而，对现存灵长类动物的大量理论和实验工作还没有阐明下颌骨形状的哪些方面的变化与牙排，下颌肌肉和下颌关节的位置变化有关，这些变化与下颌骨对内力的抵抗有关，以及这些变化如何与摄食行为和饮食有关。此外，在上新世更新世人类的牙颌形态和饮食之间的关系的经典共识-适应加工机械阻力的食物-已受到挑战，最近的推论，从饮食同位素，咬合微磨损，有限元建模，不收敛于早期人类的饮食和喂养行为的共同观点。鉴于南方古猿anamensis-A的下颌骨化石记录丰富，这种缺乏共识的情况尤其明显。afarensis谱系（4.2-3.0 Ma），记录了随着时间的推移，牙颌形态和碳同位素特征的明显变化。拟议的研究的主要重点是如何在现存的原始人（类人猿和人类）和早期南方古猿的饮食和喂养行为的轨迹变化的下颌骨形状的空间和机械的决定因素的综合调查。 本研究有三个具体目标：1。量化和比较现存（人属，庞戈，潘和大猩猩）和化石（A。anamensis、阿那木A.通过计算机断层扫描和几何形态测量学研究阿法人种; 2.通过有限元模型测试有关原始人类下颌骨形态变化的生物力学意义的特定假设; 3.评估咀嚼系统组成部分（牙列，颌关节和肌肉附着点）的空间定位在多大程度上解释了现存原始人和早期南方古猿下颌骨形态的变化。该项目将提供有关早期人类下颌骨形态的结构和功能决定因素的新数据，以帮助确定驱动这些形态变化的因素，并允许测试有关该属早期进化的适应性假设。

Among the fundamental questions about human origins is how our hominin ancestors lived. This study uses a multidisciplinary approach (paleontology, paleoecology, comparative anatomy, experimental biology) to ask questions about how extinct populations of hominins behaved on their natural landscapes. Specifically, the investigators will analyze lower jaws (mandibles), among the most commonly represented parts of the skeleton in the early human fossil record, of modern great apes and two early species of extinct hominins (Autralopithecus), to understand how the structure of the mandible is related to changes in feeding behavior and diet. The research will provide new data about how changes in diet and feeding behavior transformed our anatomy across time, permitting more robust explanations of the processes by which we became human. Broader impacts will include undergraduate, graduate and postdoctoral training in the latest analytical techniques for fossil analyses; outreach to primary and secondary school science teachers and students using hands-on experiences and web-based content designed to enhance teaching and learning about human origins; and the production of a unique collection 3D data for modern apes and rare fossil specimens that will be available to the scientific community.Mandibles are the most common element in the hominin fossil record after teeth; they are used to diagnose species, test phylogenetic hypotheses, and infer feeding behavior and diet. However, extensive theoretical and experimental work on extant primates has not clarified which aspects of variation in mandibular form are related to variation in the positions of the tooth row, jaw muscles and jaw joint, which are related to the mandible's resistance to internal forces, and how these relate to feeding behavior and diet. Furthermore, the classical consensus on the relationship between dentognathic morphology and diet in Plio-Pleistocene hominins - adaptation to processing mechanically resistant foods - has been challenged by recent inferences from dietary isotopes, occlusal microwear, and finite element modeling, which do not converge on a shared view of early hominin diets and feeding behavior. This lack of consensus is especially glaring in light of the rich fossil record of mandibles for the Australopithecus anamensis-A. afarensis lineage (4.2-3.0 Ma), which documents clear changes in dentognathic morphology and carbon-isotope signatures over time. The primary focus of the proposed research is an integrative investigation of how spatial and mechanical determinants of mandibular form track change in diet and feeding behavior in extant hominids (great apes and humans) and early Australopithecus. The research is organized under three specific aims: 1. Quantifying and comparing the location, magnitude and nature of external and internal morphological variation in mandibles of extant (Homo, Pongo, Pan, and Gorilla) and fossil (A. anamensis, A. afarensis) hominids via computed tomography and geometric morphometrics; 2. Testing specific hypotheses about the biomechanical significance of variation in hominid mandibular morphology via finite-element models; and 3. Evaluating the extent to which spatial positioning of masticatory system components (tooth row, jaw joint, and muscle attachment points) explain variation in mandibular morphology across extant hominids and early Australopithecus. The project will provide new data on the structural and functional determinants of early hominin mandibular morphology, to help identify the factors that drove these morphological changes and allow tests of adaptive hypotheses about the early evolution of the genus.