Coronosaurus

Coronosaurus is a genus of centrosaurine ceratopsian dinosaurs which contains one known species, Coronosaurus brinkmani,[1] originally classified in the genus Centrosaurus.[2] Its remains were discovered in the Oldman Formation of Alberta, Canada, dated to the Late Cretaceous (middle Campanian stage).

Discovery
Coronosaurus is known from two bone beds located in the upper unit of the Oldman Formation, of the Belly River Group. Most of the ceratopsid material, if not all, from BB 138 in Dinosaur Provincial Park, Alberta, and the MRR BB near Warner, Alberta, was referred to C. brinkmani. Bone bed 138 is located approximately fifty kilometers from Brooks, Alberta, in the Oldman Formation and 14.6 m below the contact with the Dinosaur Park Formation. It was excavated by Philip Currie between 1996 and 2000.[3] The MRR BB located approximately 180 km southwest of BB 138, is also from the Oldman Formation. These bone beds date to the middle Campanian stage of the Late Cretaceous period.[1] Both the specimens and the precise localities are archived at the Royal Tyrrell Museum of Palaeontology, in Drumheller, Alberta. The holotype of Coronosaurus is TMP 2002.68.1. It is a large adult-sized parietal with an almost complete midline bar and a partial posterior bar with left P1–P3 processes and the partially eroded right P1-P2. The specimen lacks the extreme anterior margin of the midline bar that forms the posterior wall of the frontal fontanelle and the paper-thin lateral margins that define the medial margins of the supraorbital foramina. Other significant specimens according to Ryan & Russell (2005) include TMP 2002.68.3 (a parietal), TMP 2002.68.10 (a postorbital), and TMP 2002.68.5 (supraorbitals).

Description
Coronosaurus is a medium-sized centrosaurine ceratopsid. Gregory S. Paul in 2010 estimated its body length at five meters, its weight at two tonnes.[4] It had as an adult inflated supraorbital horncores — the "brow horns" above the eye sockets — but not elongated as in Zuniceratops, chasmosaurines, and more basal centrosaurines (like Albertaceratops and Diabloceratops), that project laterally (to the sides) over the orbit. However, as a sub-adult its postorbital horncores are pyramidal in shape with a slight lateral inflection of the distal, upper, one half. Coronosaurus is unique among ceratopsians in possessing on the rear frill of the skull a number of accessory epiparietal ossifications on its posterior parietal bar that fuse to the posterior and dorsal frill surfaces. They develop through ontogeny, the growth of the individual, as short spines that may fuse along their adjacent margins into larger, irregular bone masses. They are located close to the midline of the frill in a closely packed bunch above the base of the first epiparietal (P1), the bone spur that at each side growths downwards over the large opening in each frill half. They contribute to the substance of P1 and, through fusion, form a composite epiparietal, that is equivalent to the second epiparietal (P2) normally formed in a more lateral position. The P1 bases can thus be considered the growth positions of the second epiparietals, the P2 loci. Coronosaurus has also a uniquely shaped P3 epiparietal. It is variably developed as a short tongue-like hook or tapered spike that is oriented dorsolaterally, following the curve of the frill.[1] Otherwise, as far as is known Coronosaurus resembles Centrosaurus and Styracosaurus in its morphology. For example, the nasal of Coronosaurus closely resembles that of Centrosaurus apertus in its unfused juvenile or subadult and fused adult forms and appears to have undergone a similar ontogenetic changes. Its erect, laterally compressed nasal horn core has a blunt tip that is formed from the fusion of the opposing nasals. It sits over the posterior portion of the external nares, as it does in all centrosaurines. All juvenile and most adult specimens have gently recurved anterior and posterior margins resulting in most horns having an apex that is oriented at least slightly caudally (backwards).