A potential deinocheirid ornithomimosaur from the Judith River Formation (Upper Cretaceous: Montana, U.S.A.) and its paleobiogeographic
implications

Tsogtbaatar Chinzorig, Ryuji Takasaki, Kentaro Chiba, Anthony R. Fiorillo, Yoshitsugu Kobayashi, Mototaka Saneyoshi, Shinobu Ishigaki

We describe a potential deinocheirid ornithomimosaur from the Upper Cretaceous Judith River Formation of Montana, represented by isolated left and right dentaries. Compared with ornithomimids, the dentaries exhibit distinct morphological features, including a dorsoventrally tall dentary, absence of the dorsal ridge on the cutting edge, and lack of significant symphyseal expansion. These features resemble those observed in deinocheirid
ornithomimosaurs, particularly Deinocheirus mirificus, although the fragmentary nature of the new material hinders definitive taxonomic attributions. Computed tomographic imaging reveals the presence of three major neurovascular canals that likely supplied vessels and nerves to the rhamphotheca. These canals communicate with the vascular impressions on the medial surface of the dentary. The vascular impressions indicate blood vessels running within the dermis, indicating an avian-like rhamphotheca nourishing system in Ornithomimosauria. Regardless of its taxonomic
status, the dorsoventrally deep dentary differs from known ornithomimosaurs in North America. This finding, therefore, underscores the hidden dinosaur diversity yet to be unveiled, even within well-studied dinosaur-bearing rock units that contribute to our understanding of the paleobiogeography and evolutionary history of ornithomimosaur dinosaurs.

Journal of Vertebrate Paleontology

10.1080/02724634.2025.2536844