TESTING HYPOTHESES OF LATE CRETACEOUS DINOSAUR COMMUNITY STRUCTURE AND PROVINCIALISM USING MULTIVARIATE, TRAIT-BASED APPROACHES

Studies of late Cretaceous (Campanian-Maastrichtian) dinosaur biodiversity and paleoecology in Laramidia have been the focus of extensive field collecting and research in an attempt to understand how these organisms coexisted in an extinct ecosystem. Studies utilizing fossil occurrences or stable isotopes have helped define species provinces, endemic centers and potential dietary niches, but have not accounted for the role morphological traits play in the greater community structure. In this study, we attempt to understand the role morphological traits played in assembling dinosaur communities by applying multivariate quantitative approaches to published databases of morphological traits of two of the most common herbivorous dinosaurs: ceratopsians and hadrosaurs. We also test for patterns of morphological provincialism predicting that groups of organisms coexisting spatially and temporally may exhibit sets of shared ecosystem-specific features, even if distantly related, because interactions between an individual taxon, its environment and coexisting taxa will select for these traits. Our results indicate that while some taxonomic groups exhibit some form of niche conservation, many statistically significant patterns (MANOVA, p<0.05) of community assembly are driven by losses of entire clades, such as the disappearance of centrosaurine ceratopsians and lambeosaurine hadrosaurs across the Campanian-Maastrichtian boundary resulting in a contraction of the total occupied morphospace. In these cases, it seems the surviving clades of ceratopsian (chasmosaurine) an hadrosaurs (saurolophine) may have replaced the centrosaurine and lambeosaurine clades, which became extinct at the end of the Campanian, suggesting that intraspecific trait variability was low. While this does not fully refute the idea of provincialism, it suggests that other factors, such as ontogeny, may have influenced community assembly in the Mesozoic.