The evolutionary history and palaeobiogeography of marginocephalian dinosaurs

The Marginocephalia (i.e., the horned and dome-headed dinosaurs) represent a Late Cretaceous radiation of bipedal and quadrupedal ornithischian dinosaurs that were widespread throughout western North America and Asia and remarkable for their extensive craniofacial ornamentation. The richness of the marginocephalian fossil record which includes numerous multi-individual bonebeds, articulated skeletons and isolated macrofossil remains, is essential to the ongoing characterisation of the Late Cretaceous dinosaur fauna of western North America. For example, marginocephalians are among the most abundant identifiable ornithischian taxa that constitute the dinosaur dominated macrofossil assemblages of the Dinosaur Park (76.9-74.4 Ma) and Horseshoe Canyon (73.1-67.95 Ma) formations of southern Alberta, Canada. The narrow stratigraphic distribution of the macrofossil remains of these taxa and the low contemporaneous diversity (<3 species) has prompted the recognition of discrete 'sub-formational' faunal assemblage zones. For studies focused on dinosaur evolution and palaeobiogeography, these patterns are key to understanding the selection pressures influencing the evolution of specific taxa in the wider dinosaur assemblage which are best approached in a phylogenetic context to provide the broadest understanding of the group. This study aims to test existing phylogenetic hypotheses associated with marginocephalian diversity and to utilise multiple phylogenetic-based biogeographic methods to identify areas where poor sampling of the fossil record biases our understanding of diversity and faunal turnover of these dinosaurs.