Furcatoceratops elucidans, a new centrosaurine (Ornithischia: Ceratopsidae) from the upper Campanian Judith River Formation, Montana, USA

Although ceratopsian dinosaurs have been excavated from the Judith River Formation for more than a century, their diversity within the formation remains poorly understood due to the fragmentary nature of those specimens. Here, we describe Furcatoceratops elucidans gen. et sp. nov., a new centrosaurine ceratopsid, based on a nearly complete skeleton found in the upper Judith River Formation. F. elucidans is diagnosed by several unique characters such as anteriorly oriented supraorbital horncores with slight medial curvature and anteroventral process of the nasal that laterally covers the premaxilla. Cladistic analysis recovered F. elucidans as an early-diverging centrosaurine closely related to Nasutoceratops. The holotype is inferred to be a subadult individual based on its surface textures, histological features, size and suture obliteration patterns among bones, thus providing insights into the ontogeny of ceratopsid dinosaurs. The inferred ontogenetic sequence of F. elucidans suggests that the supracranial elements co-ossified earlier than narial elements, as in the chasmosaurine Triceratops but possibly unlike in derived centrosaurines. Because most bones such as cranial and vertebral elements are disarticulated and well preserved, the holotype will serve as a useful comparative specimen for future ceratopsian research.