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了解灵长类的起源和不同分支中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。这些管道感觉到旋转头部的加速和驱动反射，这是正常运动所必需的。可以在骨科标本和化石中测量的根管弯曲半径可以预测根管的敏感性。在现存的灵长类动物和已灭绝的灵长类动物中，神经管形态的差异被归因于物种间运动行为的差异。然而，运动对管腔形态的选择方式仍存在争议。虽然有些人认为大的敏感通道适合检测缓慢的头部加速(“慢敏感假说”)，但另一些人则认为大的敏感通道适合检测快速的头部加速(“快速敏感假说”)。寻求重建运动偏好的古生物学家根据这两种假设进行了推断，得出了关于生命中总体敏捷性和头部定向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的实际数据，因此无法测试其他情景。为了完善所提出的管形态和运动功能之间的联系，并解决相互冲突的功能解释，本研究将研究表现出不同运动行为的链鼻灵长类动物的旋转头部加速。运动过程中的头部加速度将使用三维运动学分析来表征。头颅CT扫描将被用来测量椎管的曲率半径，并模拟椎管对不同方向旋转的敏感性。然后，将运动头部加速度的直接测量与敏感性的形态决定因素进行比较，以检验慢敏感和快敏感假说的预测。半规管形态可能提供关于已灭绝分类群运动的线索，这些分类群与颅后遗骸提供的信息是分开和不同的。了解行为是如何选择管道形态的，对于做出这种性质的准确推断是至关重要的。该项目将首次提供灵长类动物运动头部加速的特征。这些数据将被用来评估关于半规管形态和运动头部加速之间的适应性联系的相互竞争的假设。这将促进对灭绝灵长类动物运动适应的理解，并将有助于确定基于化石运河的运动重建的界限。此外，链鼻目动物的使用可能有利于对与灵长类起源相关的运动适应和进化转变的推断。

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.