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原始人祖先是如何生活的。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)来询问灭绝的原始人种群在其自然景观中的行为。具体地说，研究人员将分析现代类人猿和两种早期灭绝的古人类(Autralopithecus)的下颌骨(下颌骨)，以了解下颌骨的结构如何与进食行为和饮食的变化有关。下颌骨是早期人类化石记录中最常见的骨骼部分。这项研究将提供有关饮食和进食行为的变化如何随着时间的推移改变我们的解剖结构的新数据，从而能够更有力地解释我们成为人类的过程。更广泛的影响将包括本科生、研究生和博士后在化石分析的最新分析技术方面的培训；利用实践经验和旨在加强关于人类起源的教学和学习的网络内容，向中小学科学教师和学生宣传；制作独特的现代类人猿和稀有化石标本的3D数据集，供科学界使用。下颌骨是人类化石记录中最常见的元素，仅次于牙齿；它们被用于诊断物种、测试系统发育假说，以及推断进食行为和饮食。然而，关于现存灵长类动物的大量理论和实验工作并没有阐明下颌形态的哪些方面与牙排、颌肌和颌关节位置的变化有关，这些位置与下颌对内力的抵抗力有关，以及它们如何与摄食行为和饮食有关。此外，关于上更新世人类牙齿形态与饮食之间关系的经典共识--适应加工机械抵抗食物--已受到来自饮食同位素、咬合微磨损和有限元模拟的最新推断的挑战，这些推断不能收敛于早期人饮食和摄食行为的共同观点。鉴于南方古猿-A的下颌骨化石记录丰富，这种缺乏共识的情况尤为明显。阿法斯谱系(4.2-3.0 Ma)，它记录了牙齿形态和碳同位素特征随时间的明显变化。这项研究的主要重点是对现存的原始人(类人猿和人类)和早期南方古猿的下颌形态的空间和力学决定因素如何跟踪饮食和摄食行为的变化进行综合研究。这项研究有三个具体的目标：1.通过计算机断层扫描和几何形态计量学，量化和比较现存的原始人类(人、庞戈、潘和大猩猩)和化石(远古古猿、阿法尔古猿)下颌骨外部和内部形态变异的位置、大小和性质；2.通过有限元模型检验关于原始人类下颌形态变异的生物力学意义的具体假设；3.评估咀嚼系统组件(牙排、颌关节和肌肉附着点)的空间位置在多大程度上解释现存的原始人类和早期南方古猿之间的下颌形态变异。该项目将提供关于早期人下颌形态结构和功能决定因素的新数据，以帮助识别驱动这些形态变化的因素，并允许测试关于该属早期进化的适应性假说。

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.