Cranial Osteology of Fona herzogae (Dinosauria: Thescelosaurinae) from the Mussentuchit Member of the Cedar Mountain Formation

Abstract

The North American thescelosaurine ornithischian Fona herzogae (Cenomanian Mussentuchit Member of the Cedar Mountain Formation) is represented by one of the largest samples of isolated cranial elements among early diverging neornithischians. Here, we present a comprehensive cranial description of F. herzogae, utilizing advanced digitization and visualization techniques to reconstruct individual elements in high resolution with a particular focus on taxonomically and phylogenetically significant morphology. The abundance of disarticulated cranial material permits comprehensive documentation of individual elements from multiple orientations, substantially expanding the known cranial anatomy of F. herzogae and improving character evaluation across Thescelosauridae. We use these new anatomical details, together with targeted character revisions and firsthand recoding of Koreanosaurus, to improve resolution among thescelosaurid evolutionary relationships. Our analyses recover Koreanosaurus within Thescelosaurinae, strengthen support for the inclusion of several Asian taxa within this clade, and reinforce a biogeographic distinction between an Asian–North American Thescelosaurinae and a geographically restricted North American Orodrominae.