is in a state of flux. For the aforementioned reasons, it is likely that Mojoceratops, Eoceratops, and C. kaiseni belong to a distinct species, if not genus, of chasmosaurine. Specimens referred to C. russelli are all from the lower Dinosaur Park Formation, stratigraphically and morphologically separate from C. belli. Apart from the holotype and paratype several additional specimens of C. belli are known. These include AMNH 5422, ROM 843 (earlier ROM 5499) and NHMUK R4948, all (partial) skeletons with skull. The skull YPM 2016 and the skull and skeleton AMNH 5402 were noted by Campbell et al. (2016) as differing from other C. belli referred specimens in having more epiparietals, although the authors interpreted them as individual variation, but this was reconsidered when Campbell et al. (2019) interpreted these specimens as an indeterminate Chasmosaurus species closely related to Vagaceratops. The specimen CMN 2245 was referred to the Vagaceratops-like Chasmosaurus species by Fowler and Freedman Fowler (2020), who noted that "given the similarity between these two specimens (YPM 2016 and AMNH 5402) and CMN 2245, it is not clear why CMN 2245 was left in C. belli." In 2015, Nicholas Longrich presented a novel theory that posits C. belli and C. russelli are synonymous, while splitting some remains assigned to the latter to a new species, C. priscus. Because the publication was rejected, C. "priscus" remains a nomen nudum; however, the name appeared in the pre-proof of the description of Sierraceratops before being edited out for final publication. Description Chasmosaurus was a medium-size ceratopsid. In 2010 G.S. Paul estimated the length of C. belli at 4.8 metres, its weight at two tonnes; the lower Dinosaur Park Formation species would have been 4.3 metres long and weighed 1.5 tonnes. The known differences between the two species mainly pertain to the horn and frill shape, as the referred postcrania of C. russelli are poorly known. Like many ceratopsians, Chasmosaurus had three main facial horns - one on the nose and two on the brow. In both species these horns are quite short, but with the lower Dinosaur Park species they are somewhat longer, especially the brow horns, and more curved backwards. The frill of Chasmosaurus is very elongated and broader at the rear than at the front. It is hardly elevated from the plane of the snout. With C. belli the rear of the frill is V-shaped and its sides are straight. With