Doctoral Dissertation Improvement: Functional Analysis of Primate Semicircular Canal Morphology in Relation to Locomotor Head Accelerations

从化石中重建运动模式对于理解灵长类动物的起源和不同进化支的重要转变至关重要。最近的研究表明，内耳半规管的结构为运动提供了证据。这些神经管感知头部旋转的加速度，并驱动正常运动所必需的反射。椎管曲率半径可以在骨标本和化石中测量，预测椎管的敏感性。现存和已灭绝灵长类动物的椎管形态变化归因于运动行为的种间差异。然而，运动选择管形态的方式存在争议。虽然有些人认为大的敏感管道适合检测头部缓慢的加速度（“慢敏感假说”），但其他人认为大的敏感管道适合检测头部快速的加速度（“快敏感假说”）。试图重建运动偏好的古生物学家根据这两种假设进行了推断，得出了关于生命中整体敏捷性和定向头部运动模式的相反结论。由于没有关于灵长类动物头部旋转加速度的实际数据，其他情况无法进行测试。为了完善椎管形态与运动功能之间的联系，并解决相互矛盾的功能解释，本研究将研究具有不同运动行为的链状灵长类动物的旋转头部加速度。运动过程中的头部加速度将使用三维运动学分析来表征。颅CT扫描将用于测量椎管曲率半径和模拟椎管对不同方向旋转的敏感性。然后将直接测量的运动头部加速度与敏感性的形态学决定因素进行比较，以测试慢敏感和快敏感假设的预测。半规管形态可能为已灭绝类群的运动提供线索，这些线索与颅后遗骸提供的信息不同。了解行为选择对管道形态的影响是对这种性质做出准确推断的关键。这个项目将提供灵长类动物运动头部加速度的第一个特征。这些数据将用于评估关于半规管形态和运动头部加速度之间的适应性联系的竞争性假设。它将促进对已灭绝灵长类动物运动适应的理解，并有助于确定基于化石管道的运动重建的局限性。此外，链霉素的使用可能有利于推断与灵长类起源相关的运动适应和进化转变。

Reconstructing locomotor patterns from fossils is crucial for understanding the origins of primates and important transitions in various clades. Recent studies suggest that the structure of the semicircular canals of the inner ear provides evidence about locomotion. The canals sense rotational head accelerations and drive reflexes essential for normal movement. Canal radius of curvature, which can be measured in osteologic specimens and fossils, predicts canal sensitivity. Variation in canal morphology in living and, by inference, extinct primates has been attributed to interspecific differences in locomotor behavior. However, the manner in which movement selects for canal morphology is debated. While some argue that large sensitive canals are adaptive for detecting slow head accelerations (the "slow-sensitive hypothesis"), others contend that large sensitive canals are adaptive for detecting fast head accelerations (the "fast-sensitive hypothesis"). Paleontologists seeking to reconstruct locomotor preferences have extrapolated from both hypotheses to arrive at opposing conclusions about overall agility and patterns of directional head movement in life. Alternative scenarios cannot be tested because there are no actual data about rotational head accelerations in primates. To refine proposed links between canal morphology and locomotor function, and to resolve conflicting functional interpretations, this study will examine rotational head accelerations in strepsirhine primates exhibiting diverse locomotor behaviors. Head accelerations during locomotion will be characterized using 3-dimensional kinematic analyses. Cranial CT scans will be used to measure canal radii of curvature and to model canal sensitivity to rotations in different directions. Direct measurements of locomotor head accelerations will then be compared to morphologic determinants of sensitivity to test predictions of the slow-sensitive and fast-sensitive hypotheses.Semicircular canal morphology may offer clues about locomotion in extinct taxa that are separate and distinct from the information provided by postcranial remains. Understanding how behavior selects for canal morphology is critical for making accurate inferences of this nature. This project will supply the first characterization of locomotor head accelerations in primates. These data will be used to evaluate competing hypotheses about the adaptive link between semicircular canal morphology and locomotor head accelerations. It will advance understanding of locomotor adaptation in extinct primates and will help to define the limits of fossil-canal-based locomotor reconstruction. Moreover, the use of strepsirhines may advantage inferences about the locomotor adaptations and evolutionary shifts associated with primate origins.