Regaliceratops (meaning "Royal horned face") is a monospecific genus of chasmosaurine ceratopsid dinosaur from Alberta, Canada that lived during the Late Cretaceous (middle Maastrichtian stage, 68.5 to 67.5 Ma) in what is now the St. Mary River Formation. The type and only species, Regaliceratops peterhewsi, is known only from an adult individual with a nearly complete skull lacking the lower jaw, which was nicknamed "Hellboy". Regaliceratops was named in 2015 by Caleb M. Brown and Donald M. Henderson. Regaliceratops has an estimated length of 5 metres (16 ft) and body mass of 2 metric tons (2.2 short tons). The skull of Regaliceratops displays features more similar to centrosaurines, which suggests convergent evolution in display morphology in ceratopsids.
Discovery and naming In 2005, a skull of a ceratopsid was discovered by geologist Peter Hews from the St. Mary River Formation, along the Oldman River in southwestern Alberta. The skull was located in well cemented siltstone and with the tip of the snout sticking out of a cliff. The skull was excavated in 2006 and 2008 by a team of the Royal Tyrrell Museum and was removed in blocks. The excavation was described as being complicated as the specimen was in close proximity to protected spawning habitat for bull trout in the river. The specimen was nicknamed "Hellboy" due to the difficult and time-consuming excavation, in addition to the hard matrix, and the presence of small postorbital horncores with resorption pits. The specimen was subsequently named and described in 2015 by Caleb M. Brown and Donald M. Henderson. The holotype specimen, TMP 2005.055.0001, consists of a nearly complete skull that is missing only the rostrum. The skull was deformed by compression and its rear and underside are obscured by the matrix. The specimen represents an adult individual as the cranial elements are fused together and the bone surface texture is rugose, unlike that of juvenile and subadult ceratopsids. The generic name, Regaliceratops, is derived from the Latin word "regalis" (royal) and the Greek words "keras", (horn), and "ops", (face). The generic name is in reference to the crown-shaped parietosquamosal frill and the Royal Tyrrell Museum. The specific name, peterhewsi, honours the geologist Peter Hews, who discovered the type specimen. The skull was co-collected and prepared by Royal Tyrrell Museum senior technician Darren H. Tanke over a 17 month period.
Description
Size and distinguishing traits Regaliceratops was a large ceratopsian, reaching 5 metres (16 ft) in length and 2 metric tons (2.2 short tons) in body mass. Brown & Henderson (2015) diagnosed Regaliceratops based on the presence of a single, midline epiparietal ossification that is offset from the plane of the frill and other epiparietals towards the rostrum with parietals projecting towards the posterior end that have a roughly triangular transverse cross-section; a prominent midline ridge on that parietal that merges with the median epiparietal; paired epiparietal ossifications that are long, flat, and roughly pentagonal shaped; a prominent postorbital ridge that runs diagonally from the supraorbital horncore to the base of the squamosal; parietal fenestrae that are small in size to orbit as in Kosmoceratops; and nasal horncores that are larger than the postorbital horncores as in Chasmosaurus belli and Vagaceratops.
Cranium
The snout of the holotype specimen is short and tall, although it has been exaggerated by the tectonic shortening of the skull. The paired premaxillae form the median premaxillary septum, with the rostral portion of the median premaxillary septum being thin forming the prominent septal fossa. Unlike Triceratops and Titanoceratops, the prominent septal fossa lacks the accessory strut. The fossa is further thinned at the caudal portion and is spread throughout by the presence of a large interpremaxillary fenestra as in Anchiceratops, Arrhinoceratops and Triceratops. Regaliceratops, and other chasmosaurines, has the caudal wall of the interpremaxillary fenestra bounded by a condensed narial strut that moves back and forth from the floor of the premaxillae to the upper process of the premaxillae. Unlike Titanoceratops and Triceratops, the narial strut isn't as broad and triangular but is, instead, sinuous in shape. The premaxillae flare towards the sides which form the rostroventral margin of the external nares on the rostral and ventral margins. The maxillary process projects caudodorsally from the flared underside aspect of the premaxilla. Unlike Campanian chasmosaurines such as Chasmosaurus and Utahceratops, the caudoventral process of Regaliceratops tapers caudally without forking, and inserts between the maxilla and nasal towards the sides. The upper margin of the external naris is formed by the rostral process and horncore base, and extends caudal to the rostral margin of the maxillary tooth row. As in Bravoceratops, the nasal shows no constriction situated caudal to the horncore. As in Chasmosaurus, the midpoint of the horncore is positioned at the caudal extreme of the external naris. The nasal horncore has an estimated preserved height of 148 mm and an estimated total height range of 240 to 280mm when the side slopes of the horncore are extrapolated. The nasal horncore is straight and has a tear drop shape in horizontal cross section.
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