DISSERTATION RESEARCH: Evolution of the Jaw Musculature of Archosaurs: The Transitions to the Modern Avian and Crocodilian Conditions and their Functional Implications

颌部肌肉系统是脊椎动物头部的一个固有的重要系统，它占据着一个称为内收肌的空间。颌部肌肉显然是喂养装置的关键元素，同时通过施加在头骨上的力来塑造头骨。同样，这些肌肉占据头部的空间，因此限制了相邻系统(如眼睛、耳朵、喉咙)的大小和形状。这个项目分析了始祖龙(包括今天的鸟类和鳄鱼，以及中生代的恐龙、翼龙和其他灭绝的形式)中颌部肌肉的进化模式，以阐明现代条件的演变，以及恐龙和其他灭绝的类群的摄食行为和生物学。然而，化石只保存了坚硬的部分(骨骼和牙齿)，因此该项目的一个关键要素是重建灭绝的原始龙内收肌的软组织成分，然后为功能解释提供基础。关于内收肌软组织的假说将在现有的系统发育支架(EPB)方法的背景下进行测试，根据该方法，化石类(恐龙、化石鳄鱼)的现代亲属(鸟类、鳄鱼、蜥蜴)提供关于软组织与它们在骨骼上留下的特征之间的关系的信息。相关的软组织(肌肉、肌腱、神经、动脉)将在现代动物中使用解剖、注射和放射成像等方法进行研究，以发现软组织的骨特征。然后，将对始祖龙化石进行调查，以了解这些特定的骨骼特征(例如，肌肉疤痕、神经孔)。关键化石标本的CT扫描将是一个关键工具，因为它不仅将提供内收肌周围骨骼特征的数据，还将产生3D数字数据集，从中可以自动进行高精度测量，并可以实施有限元分析等工程工具。所研究的一些特定的肌肉模式包括(1)内收肌内的模式，揭示了颌骨肌肉的同源性和功能，以及(2)内收肌外的模式，它影响着颌骨肌肉与邻近的眼睛和耳朵之间的空间和功能相互作用。鉴于K-12对所有恐龙的持续兴趣，这个项目将吸引人们的注意，这将提供新的机会，利用恐龙作为工具来教授一般的科学知识，预计的场所是媒体、学校或其他公开露面，以及互联网。

Jaw musculature is an inherently important system in the vertebrate head occupying a space called the adductor chamber. Jaw muscles obviously are critical elements of the feeding apparatus, simultaneously sculpting the skull via the forces they impose on it. Likewise, these muscles occupy space in the head and so constrain the sizes and shapes of adjacent systems (e.g., eyes, ears, throat). This project analyzes evolutionary patterns of jaw musculature among archosaurs (the group of animals including birds and crocodilians today and dinosaurs, pterodactyls, and other extinct forms in the Mesozoic Era) to elucidate not only the evolution of the modern condition but also the feeding behavior and biology of dinosaurs and other extinct taxa. Fossils, however, preserve only hard parts (bones and teeth), and thus a key element of the project is to reconstruct the soft-tissue components of the adductor chamber of extinct archosaurs which will then provide a basis for functional interpretation. Hypotheses about the soft tissues in the adductor chamber will be tested in the context of the extant phylogenetic bracket (EPB) approach, whereby the modern relatives (birds, crocodilians, lizards) of the fossil group (dinosaurs, fossil crocodilians) provide information on the relationship between soft tissues and the signatures they leave on the bones. Pertinent soft tissues (muscles, tendons, nerves, arteries) will be studied in the modern animals using methods such as dissection, injection, and radiologic imaging to discover the bony signatures of the soft tissues. Fossil archosaurs will then be surveyed for these specified bony features (e.g., muscle scars, nerve foramina). CT scanning of pivotal fossil specimens will be a critical tool in that it will not only provide data on bony features surrounding the adductor chamber but also will yield 3D digital datasets from which highly accurate measurements can be made automatically and engineering tools such as finite element analysis can be implemented. Some of the specific muscular patterns studied include (1) patterns inside the adductor chamber that shed light on jaw muscle homology and function, and (2) patterns outside the adductor chamber that have bearing on the spatial and functional interactions between the jaw muscles and the nearby eye and ear. Given the continual K-12 interest in all things dinosaurian, the attention this project will attract will provide new opportunities to use dinosaurs as tools to teach about science in general, with expected venues being media outlets, school or other public appearances, and the internet.