The ceratosaurian theropod dinosaur Limusaurus inextricabilis is known from numerous skeletons from the Late Jurassic of Xinjiang, China, and has recently been recognized as a member of the Noasauridae. In Chapter 2 I describe the osteology of Limusaurus inextricabilis based on gross anatomical and computed tomographic data from an ontogenetic series of skulls and postcranial skeletons that includes toothed juveniles and edentulous subadults-adults. In Chapter 3, the hypothesis of synonymy for the toothed juvenile and large edentulous specimens referred to Limusaurus is tested using multiple lines of evidence. Results from analyses of computed tomographic, osteohistological, phylogenetic, and stable isotopic datasets failed to reject the hypothesis of synonymy and indicate that Limusaurus inextricabilis lost its teeth throughout its postnatal ontogeny, a phenomenon that is termed “ontogenetic edentulism”. In Chapter 4, I describe evidence of ontogenetic edentulism in a Late Cretaceous oviraptorosaurian theropod and an Early Cretaceous bird. I then synthesize neontological and paleontological data regarding the evolutionary development of beaks and teeth, and the evolutionary history of tooth loss in numerous vertebrate lineages to generate a new model for the macroevolution of tooth loss in vertebrates. In Chapter 5, the paratype specimen of Chuandongocoelurus primitivus is re-described as a noasaurid ceratosaur. Available detrital-zircon ages and sequence stratigraphic data for Sichuan Basin strata are re-analyzed and suggest the new taxon and Limusaurus lived penecontemporaneously in what is now China.