Collaborative Research: Comparative morphological analysis of the hand and wrist in Ardipithecus ramidus and Miocene hominoids

440万年前的始祖地猿（Ardipithecus ramidus）可能代表了最古老的人类祖先之一，它对人类和黑猩猩从最后一个共同祖先开始的进化分歧具有潜在的关键见解。建立这种差异的原始条件（或“起点”）将对人类起源和进化生物学研究的几乎每个方面产生革命性的影响。出乎意料的是，雷姆达斯猿的骨骼被描述为与现存猿类的不同之处，超出了此前的预测——相反，它与中新世早期的更原始的猿类相似。特别是，一些人认为，手和手腕保留了与谨慎攀爬和掌部运动（使用伸展的手腕和负重的手掌，适应在树枝上移动）有关的特征。然而，大部分的解剖结构还没有在严格的、定量的背景下进行检验，与中新世猿的比较也很有限。该项目将使用三维形态计量学分析始祖和现存灵长类动物和化石物种的广泛比较样本，以验证以下假设：1)始祖使用手的方式与现代猿类使用的高级垂直攀爬、悬浮和/或指关节行走的方式不一致；2)始祖猿是一种古人类（即，与黑猩猩相比，与人类的关系更近）。如果这些假设成立，那么古人类起源的模型就不能假设一个高度悬吊或指关节行走的祖先，或者一个从事剧烈垂直攀登的祖先。因此，对许多人类适应的解释将不得不被彻底修改。大多数标本的所有度量数据和生成的3D数字模型将通过公共在线数据库或提供给保存原始材料的博物馆。重要的是，这些3D模型构成了来自多个国内外机构的不可替代的化石和骨骼材料的记录。该奖项支持早期职业科学家，包括一名亚裔美国首席研究员（PI），其中一名联合首席研究员将促进美国和西班牙研究人员之间的合作。最后，该项目为学生提供了学习解剖学成像和计算机建模技能的重要机会，这些技能在基础科学和生物医学中是不可或缺的。

The 4.4 million year old fossil species Ardipithecus ramidus may represent one of the oldest human ancestors, and it holds potentially critical insights into the initial evolutionary divergence of humans and chimpanzees from their last common ancestor. Establishing the primitive condition (or 'starting point') for that divergence would have transformative implications for nearly every aspect of research on human origins and evolutionary biology. Unexpectedly, the skeleton of Ar. ramidus has been described as differing from that of the living apes more than had been predicted - instead resembling that of more primitive apes from the early Miocene epoch. In particular, some have argued that the hand and wrist retain features related to cautious climbing and palmigrady (use of an extended wrist and weight-bearing palm, adapted for moving above branches). Much of the anatomy, however, has not been examined in a rigorous, quantitative context, and comparisons with Miocene apes have been limited. The project will analyze Ar. ramidus and a broad comparative sample of extant primates and fossil species using three- dimensional (3D) morphometrics to test the hypotheses that: 1) Ar. ramidus used its hands in a manner inconsistent with advanced vertical climbing, suspension, and/or knuckle-walking as used by living apes; and 2) Ar. ramidus is a hominin (i.e., more closely related to humans than chimpanzees). If these hypotheses are upheld, then models of hominin origins cannot assume a highly suspensory or knuckle- walking ancestor, or one that engaged in vigorous vertical climbing. Consequently, explanations for many human adaptations would have to be drastically modified. All metric data and the generated 3D digital models of most specimens will be available via a public online database or provided to museums housing the original material. Importantly, the 3D models constitute a record of irreplaceable fossils and skeletal material from several domestic and international institutions. This award supports early-career scientists, including one Asian American principal investigator (PI), and one of the co-PIs will foster collaboration between American and Spanish researchers. Finally, the project provides vital opportunities for students to learn skills in anatomical imaging and computer modeling, which are indispensable in the basic sciences and biomedicine.