| Description |
Recent discoveries demonstrate that Campanian dinosaur assemblages across the western North American subcontinent (Laramidia) exhibit basin-scale endemism, with each sedimentary basin possessing its own unique assemblage, and an apparent higher-level biogeographic boundary between northern and southern Laramidia. Subsequently, during the Maastrichtian, most taxa are present in multiple basins, with some forms supporting the presence of distinct northern/southern provinces, whereas others are more cosmopolitan. Despite these dinosaur biogeographic data, little attention has been paid to other vertebrate groups. To test these biogeographic hypotheses, I examined the alpha taxonomy, evolution, and paleobiogeography of the paracryptodiran turtle clade Baenidae using a newly-generated species-level phylogeny. Baenids were one of the most diverse and abundant turtle clades during the Late Cretaceous, are restricted to North America, and have a well-sampled fossil record, making them an ideal study system for examining Laramidian biogeography. I first assessed the taxonomic affinities of newly discovered baenid turtles from the Upper Cretaceous (Campanian) Kaiparowits Formation of southern Utah. I found that at least five distinct baenid species inhabited the Kaiparowits Basin during the Campanian. These taxa include Denazinemys nodosa, previously known from Texas and New Mexico, Boremys grandis, previously known from New Mexico only, and three new iv taxa that appear to have been endemic to southern Utah. These newly described taxa include two new species of Neurankylus and a morphologically unique pig-nosed taxon. Using new morphologic data from the Kaiparowits specimens, I conducted a comprehensive phylogenetic analysis on the clade, utilizing 106 characters and 32 ingroup taxa. Based on occurrences alone, Campanian baenid assemblages display distinct northern and southern provinces with no taxonomic overlap. To investigate the evolutionary patterns of this biogeographic signal, I applied a dispersal-extinction-cladogenesis model to the strict consensus tree and three randomly selected most parsimonious trees from my phylogenetic analysis. This study reveals that the ancestral ranges for basal baenid branches were cosmopolitan across either Laramidia or all of North America. More derived baenids (i.e., subclade Baenodda) possessed ancestral ranges in the area of Montana, Wyoming, and the Dakotas, and the analysis reconstructs multiple individual lineages then dispersing to southern Laramidia and Alberta. |
