RECENT DINOSAUR DISCOVERIES IN THE WESTERN INTERIOR BASIN AND THEIR IMPLICATIONS FOR LATE CRETACEOUS BIOGEOGRAPHY AND DINOSAURIAN EVOLUTION

The Western Interior Basin (WIB) is renowned for its dinosaurs, playing a key role in our understanding of their evolution, biogeography, and speciation. Most of the data has come from more highly collected localities in the northern portions of the WIB. Southern portions have played a less prominent role but have become a larger part more recently. Latitudinal differences in communities have led to hypotheses about dinosaur provinciality, particularly during the Late Cretaceous. Recently identified dinosaurs from the southern WIB have led to more important new data for these hypotheses. In opposition to the provinciality hypothesis, the western side of the Western Interior Seaway had few topographic barriers for dinosaur movement. Recent work has also suggested different species were not cotemporal and this diachroneity of fossil assemblages makes comparisons more difficult. We identify new dinosaurs from the southern WIB, including new chasmosaurine ceratopsids, and place them into phylogenetic analyses, providing evolutionary context. We recover some clades in discrete geographic regions, but many are recovered with taxa from both the north and south. This suggests similar resources (supported by similar vegetation) available throughout much of the WIB, allowing closely-related species to move freely. The ability to move through much of the WIB, but with different species present throughout, even in geographically-close regions, has important implications for dinosaur evolution. Distinct, but shorter, temporal ranges for various distinct species suggest shorter species durations and potentially high species turnover among dinosaurs, particularly compared to other large terrestrial vertebrates. Other implications regard paleobiology and behavior. More specialization can lead to more extreme niche partitioning, allowing available resources to be utilized by different species, and more diverse ecosystems can then support a wider array of species. The opposite side of the spectrum suggests more generalists, particularly regarding diets, allowing them to utilize different resources but not requiring them to be tied to any particular resource as a limiting factor. The presence of these distinct dinosaurs provides important new data for interpreting the diversity and evolution of dinosaurs in the WIB.