Dissertation Improvement Grant: A Comparative Study of the Hand and Wrist in Cebus apella and Saimiri sciureus

人类学家感兴趣的是识别早期原始人类化石（人类及其最近的两足亲属）的手和手腕的骨骼特征，这些骨骼特征可能预测石器制造能力，因为石器是在化石沉积物中发现的，其中已经发现了不止一个原始人类物种。黑猩猩传统上被用作早期原始人类手的模型，因为它们与人类有着密切的遗传关系，并且在野外使用工具。 卷尾猴与人类的亲缘关系不那么近，在圈养条件下，它们使用工具的能力与黑猩猩不相上下。 卷尾猴在猴子中是独一无二的，因为它们经常在野外用物体撞击树木。 敲打可能是预先适应的工具制作行为，因此，卷尾猴可能提供一个替代的非人类灵长类动物模型，以确定在早期原始人类的化石手，反映与冲击和有力的操纵stones.The问题的手的压力，这项研究所解决的问题是是否有卷尾猴的手肌肉和骨骼的功能，反映其独特的操纵行为。 答案如下。首先，将比较Cebus apella（簇绒卷尾猴）和Saimiri sciureus（普通松鼠猴，卷尾猴的近亲）尸体手部肌肉的相对横截面积。 横截面积反映了肌肉施加力量的潜力，并通过测量其体积和纤维长度来估计。 其次，这些肌肉的相对杠杆作用（即，它们的杠杆臂）将通过被动地移动每个手关节同时测量（1）关节的全部运动范围和（2）肌腱穿过关节移动的距离来估计。这些测量将允许估计每块肌肉施加扭矩的潜力，即每块肌肉在关节处旋转骨骼的相对能力。 最后，在可能的情况下，将识别、描述和测量反映这些肌肉的相对面积和杠杆臂的骨骼特征。 据预测，卷尾猴将有一些手部肌肉，能够产生相对更大的扭矩比松鼠猴，这些肌肉将与独特的骨骼特征。这些数据对于分析操纵能力至关重要。它们以前都没有得到任何物种。一旦在卷尾猴中发现了具有大扭矩电位的肌肉，这些肌肉就可以在未来的研究中使用肌电图进行测试，以确定它们是否确实在撞击行为中被强烈招募。本研究中使用的技术和跨学科方法的培训将在研讨会上提供给其他研究人员，在亚利桑那州立大学提供给本科生和研究生，在亚利桑那州立大学的IGERT形式功能神经肌肉骨骼适应项目（NSF#9987619）赞助的开放日上提供给高中生，包括代表性不足的群体，PI和Co-PI都与之相关。 广泛传播所收集的数据，技术和跨学科的方法将允许全球范围内的研究合作，使用卷尾猴作为替代的非人灵长类动物模型在手功能的临床研究。

Identifying skeletal features in the hands and wrists of early fossil hominid species (humans and their closest bipedal relatives) that may predict stone tool-making capabilities is of interest to anthropologists, because stone tools are found in fossil deposits where more than one hominid species has been recovered. Chimpanzees have traditionally been used as a model for early hominid hands because of their close genetic relationship to humans and their use of tools in the wild. Capuchin monkeys, less closely related to humans, rival chimpanzees in their tool-using abilities in captivity. Capuchins are unique among monkeys in that they frequently pound objects against trees in the wild. Pounding may be pre-adaptive for tool-making behaviors; therefore, capuchins may provide an alternative nonhuman primate model for identifying features in the fossil hands of early hominids that reflect stresses on the hand associated with pounding and forceful manipulation of stones.The question addressed by this study is whether there are features of capuchin hand muscles and bones that reflect their distinctive manipulative behaviors. The answer will be approached as follows. First, relative cross-sectional areas of cadaver hand muscles will be compared in Cebus apella (tufted capuchin) and Saimiri sciureus (common squirrel monkey, a close relative of capuchins). Cross-sectional area reflects a muscle's potential to exert force and is estimated by measuring its volume and its fiber length. Second, relative leverage of these same muscles (i.e., their lever arms) will be estimated by passively moving each hand joint while simultaneously measuring (1) the joint's full range of motion and (2) the distance moved by the muscle tendon crossing the joint. These measurements will allow estimation of each muscle's potential to exert torque, i.e. the relative ability of each muscle to rotate a bone at a joint. Finally, skeletal features that reflect relative areas and lever arms of these muscles will be identified, described and measured, where possible. It is predicted that capuchins will have some hand muscles that are capable of generating relatively greater torques than in squirrel monkeys, and that these muscles will be associated with distinct skeletal features. These data are essential to analysis of manipulative capabilities. They have not been previously obtained for either species. Once muscles with large torque potentials have been identified in the capuchins, these muscles can be tested in a future study using electromyography, to determine whether they are indeed strongly recruited during pounding behaviors. Training in the techniques and interdisciplinary approach used in this study will be offered to other researchers at workshops, to undergraduate and graduate students at Arizona State University, and to high school students, including underrepresented groups, at open houses sponsored by the IGERT Neural & Musculoskeletal Adaptations in Form & Function program (NSF#9987619) at Arizona State University, to which both the PI and Co-PI are attached. Broad dissemination of the collected data, techniques, and interdisciplinary approach will allow for research collaborations worldwide to use the capuchin as an alternative nonhuman primate model in clinical research on hand function.