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.
