Editing Chasmosaurus (section)

==Discovery and species==
[[File:Hunting dinosaurs in the bad lands of the Red Deer River, Alberta, Canada; a sequel to The life of a fossil hunter (1917) (20765045131).jpg|left|thumb|[[George F. Sternberg]] preparing a ''C. belli'' skull in 1914]] 
In 1898, at Berry Creek, Alberta, [[Lawrence Lambe|Lawrence Morris Lambe]] of the [[Geological Survey of Canada]] made the first discovery of ''Chasmosaurus'' remains; [[holotype]] NMC 491, a [[parietal bone]] that was part of a neck frill.<ref name="ageofdinosaurschasmosaurus"/> Although recognizing that his find represented a new species, Lambe thought this could be placed in a previously known short-frilled ceratopsian genus: ''[[Monoclonius]]''.<ref name="ageofdinosaurschasmosaurus"/> He erected the new species ''Monoclonius belli'' to describe his findings.<ref name="ageofdinosaurschasmosaurus"/> The [[specific name (zoology)|specific name]] honoured collector Walter Bell.<ref>Lambe, L.M., 1902, "New genera and species from the Belly River Series (mid-Cretaceous)", ''Geological Survey of Canada Contributions to Canadian Palaeontology'' '''3'''(2): 25–81</ref>

However, in 1913, [[Charles Hazelius Sternberg]] and his sons found several complete "M. belli" skulls in the middle [[Dinosaur Park Formation]] of [[Alberta]], [[Canada]].<ref name="ABS09">{{cite journal|last=Arbour, V.M.|author-link=Victoria Arbour|author2=Burns, M. E.|author3=Sissons, R. L.|year=2009|title=A redescription of the ankylosaurid dinosaur ''Dyoplosaurus acutosquameus'' Parks, 1924 (Ornithischia: Ankylosauria) and a revision of the genus|journal=Journal of Vertebrate Paleontology|volume=29|issue=4|pages=1117–1135|doi=10.1671/039.029.0405|bibcode=2009JVPal..29.1117A |s2cid=85665879}}</ref> Based on these finds, Lambe (1914) erected ''Protorosaurus'' ("before ''[[Torosaurus]]''"),<ref>Lambe, L.M., 1914, "On the forelimb of a carnivorous dinosaur from the Belly River Formation of Alberta, and a new genus of Ceratopsia from the same horizon, with remarks on the integument of some Cretaceous herbivorous dinosaurs", ''The Ottawa Naturalist'' '''27'''(10): 129–135</ref> but that name was preoccupied by the Permian reptile ''[[Protorosaurus]]'', so he subsequently created the replacement name ''Chasmosaurus'' in February 1914. The name ''Chasmosaurus'' is derived from Greek χάσμα, ''khasma'', "opening" or "divide" and refers to the very large parietal fenestrae in the skull frill. Lambe now also assigned a [[paratype]], specimen NMC 2245 found by the Sternbergs in 1913 and consisting of a largely complete skeleton, including skin impressions.<ref>Lambe, L.M., 1914, "On ''Gryposaurus notabilis'', a new genus and species of trachodont dinosaur from the Belly River Formation of Alberta, with a description of the skull of ''Chasmosaurus belli''", ''The Ottawa Naturalist'' '''27''': 145–155</ref>
[[File:Royal Tyrell Chasmosaurus russelli.jpg|left|thumb|''C. russelli'', [[Royal Tyrrell Museum]]]]
Since that date, more remains, including skulls, have been found that have been referred to ''Chasmosaurus'', and several additional [[species]] have been named within the genus.<ref name="ageofdinosaurschasmosaurus"/> Today some of these are considered to only reflect a morphological variation among the known sample of ''Chasmosaurus belli'' skulls;<ref name="ageofdinosaurschasmosaurus"/> others are seen as valid species of ''Chasmosaurus'' or as separate genera. In 1933 [[Barnum Brown]] named ''Chasmosaurus kaiseni'', honouring [[Peter Kaisen]] and based on skull AMNH 5401, differing from ''C. belli'' in having very long brow horns.<ref>Brown, B., 1933, "A new longhorned Belly River ceratopsian", ''American Museum Novitates'' '''669''': 1–3</ref> This form is perhaps related to ''Chasmosaurus canadensis'' ('from Canada') named by Thomas M. Lehman in 1990.<ref name="Lehman1990">T.M. Lehman, 1990, "The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics", In: K. Carpenter and P. J. Currie (eds.), ''Dinosaur Systematics: Perspectives and Approaches'', Cambridge University Press, Cambridge, pp. 211–229</ref> The latter species, originally'' Monoclonius canadensis'' Lambe 1902, had been described as ''Eoceratops canadensis'' by Lambe in 1915. ''Eoceratops'' and the long-horned ''Chasmosaurus kaiseni'' were thought to probably be exemplars of ''Mojoceratops'' by Nicholas Longrich,<ref name="Longrich2010">{{Cite journal|author=Nicholas R. Longrich|year=2010|title=''Mojoceratops perifania'', A New Chasmosaurine Ceratopsid from the Late Campanian of Western Canada|journal=Journal of Paleontology|volume=84|issue=4|pages=681–694|doi=10.1666/09-114.1|bibcode=2010JPal...84..681L |s2cid=129168541}}</ref> although different teams of researchers have found ''Mojoceratops'' to be a synonym of ''Chasmosaurus russelli''. Campbell and colleagues, in their 2016 analysis of ''Chasmosaurus'' specimens found ''Eoceratops'' and ''C. kaiseni'' to be referable to ''Chasmosaurus'' sp. due to the lack of the parietal preserved in the holotypes of both.<ref name="Campbelletal2016">Campbell, J.A., Ryan, M.J., Holmes, R.B., and Schröder-Adams, C.J. (2016). [http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0145805 A Re-Evaluation of the chasmosaurine ceratopsid genus ''Chasmosaurus'' (Dinosauria: Ornithischia) from the Upper Cretaceous (Campanian) Dinosaur Park Formation of Western Canada.] ''PLoS ONE'', '''11'''(1): e0145805. {{doi|10.1371/journal.pone.0145805}}</ref> [[Richard Swann Lull]] in 1933 named an unusual, short-muzzled skull, specimen ROM 839 (earlier ROM 5436) collected in 1926, as ''Chasmosaurus brevirostris'', "with a short snout".<ref name="Lull1933">Lull, R.S., 1933, ''A revision of the Ceratopsia or horned dinosaurs''. Memoirs of the Peabody Museum of Natural History '''3'''(3): 1–175</ref> This has been seen as a [[junior synonym]] of ''C. belli''.<ref name="Lehman1990"/>

[[Charles Mortram Sternberg]] added ''Chasmosaurus russelli'' in 1940, based on specimen NMC 8800 from southwestern Alberta (lower [[Dinosaur Park Formation]]). The specific name honours [[Loris Shano Russell]].<ref name="ABS09" /><ref>Sternberg, C.M., 1940, "Ceratopsidae from Alberta", ''Journal of Paleontology'' '''14'''(5): 468–480</ref> In 1987, [[Gregory S. Paul]] renamed ''[[Pentaceratops]] sternbergii'' into ''Chasmosaurus sternbergi'',<ref>Paul, G.S., 1987, "The science and art of reconstructing the life appearance of dinosaurs and their relatives: a rigorous how-to guide", pp 4–49 in: ''Dinosaurs Past and Present Volume II'', Natural History Museum of Los Angeles County</ref> but this has found no acceptance. In 2000, George Olshevsky renamed ''Monoclonius recurvicornis'' Cope 1889 into ''Chasmosaurus recurvicornis'' as its fossil material is likely chasmosaurine;<ref>Olshevsky, G. 2000. ''An Annotated Checklist of Dinosaur Species by Continent''. George Olshevsky, Publications Requiring Research, San Diego, 157 pp</ref> this is a ''[[nomen dubium]]''. Thomas Lehman described ''Chasmosaurus mariscalensis'' in 1989 from [[Texas]],<ref>Lehman, T.M., 1989, "''Chasmosaurus mariscalensis'', sp. nov., a new ceratopsian dinosaur from Texas", ''Journal of Vertebrate Paleontology'', '''9'''(2): 137–162</ref> which has now been renamed ''[[Agujaceratops]]''.<ref name="Lucas">{{Cite journal|vauthors=Lucas SG, Sullivan RM, Hunt AP |year=2006 |title=Re-evaluation of Pentaceratops and Chasmosaurus (Ornithischia: Ceratopsidae) in the Upper Cretaceous of the Western Interior |journal=New Mex Mus. Nat. Hist. Sci. Bull. |volume=35 |pages=367–370}}</ref> 
[[File:VagaceratopsCMN.jpg|thumb|left|Holotype of ''C. irvinensis'' at [[Canadian Museum of Nature]]]]
The most recently described species is ''Chasmosaurus irvinensis'' named in 2001,<ref>R.B. Holmes, [[Catherine Forster|C.A. Forster]], M.J. Ryan and K.M. Shepherd, 2001, "A new species of ''Chasmosaurus'' (Dinosauria: Ceratopsia) from the Dinosaur Park Formation of southern Alberta", ''Canadian Journal of Earth Sciences'' '''38''': 1423–1438</ref> which stems from the uppermost beds of the [[Dinosaur Park Formation]]. This species was given its own genus, ''[[Vagaceratops]]'', in 2010.<ref name="Sampson">{{Cite journal|author1=Scott D. Sampson |author2=Mark A. Loewen |author3=Andrew A. Farke |author4=Eric M. Roberts |author5=Catherine A. Forster |author6=Joshua A. Smith |author7=Alan L. Titus |year=2010 |title=New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism |journal=PLOS ONE |volume=5 |issue=9 |pages=e12292 |doi=10.1371/journal.pone.0012292 |pmid=20877459 |pmc=2929175 |bibcode=2010PLoSO...512292S |doi-access=free }}</ref> However, Campbell et al. (2019) referred ''Vagaceratops'' back to ''Chasmosaurus''.<ref name=":0">{{Cite journal|last1=Campbell|first1=James Alexander|last2=Ryan|first2=Michael J.|last3=Schroder-Adams|first3=Claudia J.|last4=Holmes|first4=Robert B.|last5=Evans|first5=David C.|date=2019-08-08|title=Temporal range extension and evolution of the chasmosaurine ceratopsid 'Vagaceratops' irvinensis (Dinosauria: Ornithischia) in the Upper Cretaceous (Campanian) Dinosaur Park Formation of Alberta|url=https://journals.library.ualberta.ca/vamp/index.php/VAMP/article/view/29356|journal=Vertebrate Anatomy Morphology Palaeontology|language=en|volume=7|pages=83–100|doi=10.18435/vamp29356|issn=2292-1389|doi-access=free}}</ref>  As Fowler and Fowler found ''Vagaceratops'' likely to be the sister taxon of ''Kosmoceratops'' in 2020, they suggested it should be maintained as a distinct genus from ''Chasmosaurus'', as its placement would probably remain unstable until chasmosaurines are better understood.<ref name=":1">{{Cite journal|last1=Fowler|first1=Denver W.|last2=Fowler|first2=Elizabeth A. Freedman|date=2020-06-05|title=Transitional evolutionary forms in chasmosaurine ceratopsid dinosaurs: evidence from the Campanian of New Mexico|journal=PeerJ|language=en|volume=8|pages=e9251|doi=10.7717/peerj.9251|pmid=32547873|pmc=7278894|issn=2167-8359|doi-access=free}}</ref>
[[File:VagaceratopsCMNSkull.jpg|thumb|Skull replica of ''Chasmosaurus irvinensis'', sometimes considered its own genus ''[[Vagaceratops]]'']]
The species ''Mojoceratops perifania'' was based on [[holotype]] specimen [[Royal Tyrrell Museum of Paleontology|TMP]]&nbsp;1983.25.1 consisting of a partial [[skull]] including the parietal and from the [[paratype]]s TMP&nbsp;1999.55.292, an isolated lateral ramus of a right parietal, and NMC&nbsp;8803, central bar and lateral rami of parietals. Specimens [[American Museum of Natural History|AMNH]]&nbsp;5656, NMC&nbsp;34832 and TMP&nbsp;1979.11.147, and (tentatively) AMNH&nbsp;5401 and NMC&nbsp;1254 were also referred to the genus. All specimens assigned to ''Mojoceratops'' were collected from the [[Dinosaur Park Formation]] (late [[Campanian]], 76.5–75 [[Mya (unit)|ma]]) of the [[Belly River Group]] of [[Alberta]] and [[Saskatchewan]], western [[Canada]]. ''Mojoceratops'' was named by Nicholas R. Longrich in [[2010 in paleontology|2010]] and the [[type species]] is ''Mojoceratops perifania''. The generic name is derived from [[Mojo (African-American culture)|mojo]] and the [[specific name (zoology)|specific name]] means "conspicuous pride" in Greek, both referring to the skull frill. The species is based on [[fossils]] thought by other researchers to belong to ''Chasmosaurus''.<ref name="Longrich2010"/>

The species ''Chasmosaurus kaiseni'', known from specimen AMNH 5401, a nearly complete (but partially restored) skull on display at the [[American Museum of Natural History]], was considered to share features in common with ''Mojoceratops perifania'' and therefore was considered a possible synonym. However, the parietal (back margin of the frill) is not preserved, and was restored with plaster based on specimens of ''Chasmosaurus'', which caused confusion among scientists in previous decades, because the parietal bone is critical for determining differences between species in ceratopsids like ''Chasmosaurus'' and ''Mojoceratops''. ''Chasmosaurus kaiseni'' was then by Longrich regarded as a ''[[nomen dubium]]'', rather than as the senior synonym of ''M. perifania''. Longrich also regarded the holotype of ''Eoceratops'' as probably being an exemplar of ''Mojoceratops''. He considered it too poorly preserved for a reliable determination, especially as it belonged to a juvenile individual, and regarded it too as a ''nomen dubium'', rather than as the senior synonym of ''M. perifania''.<ref name="Longrich2010"/> A 2016 overview of ''Chasmosaurus'' found ''C. kaiseni'' and ''Eoceratops'' to be referable to ''Chasmosaurus'' sp. due to the lack of the parietal preserved in the holotypes of both.<ref name=Campbelletal2016/>
[[File:Chasmosaurus kaiseni.jpg|thumb|Holotype of ''C. kaiseni'', which has also been considered a specimen of ''Mojoceratops'', which itself is probably a synonym of ''C. russelli'']]
Following the original assignment of the holotype and other skulls to ''Mojoceratops'', several teams of researchers published work questioning the validity of this new genus. In 2011, Maidment & Barrett failed to confirm the presence of any supposedly unique features, and argued that ''Mojoceratops perifania'' was a synonym of ''Chasmosaurus russelli''. Campbell and colleagues, in their 2016 analysis of ''Chasmosaurus'' specimens, agreed with the conclusions of Maidment & Barrett, adding that some supposedly unique features, such as grooves on the parietal bone, were actually also present in the holotype of ''C. russelli'' and, to various degrees, in other ''Chasmosaurus'' specimens. This variability, they argued, strongly suggested that ''Mojoceratops'' was simply a mature growth stage of ''C. russelli''.<ref name =Campbelletal2016/> Recently, the referral of ''Eoceratops'', ''C. kaiseni,'' and ''Mojoceratops'' to ''C. russelli'' was considered doubtful as the holotype of ''C. russelli'' is actually from the upper Dinosaur Park Formation, according to recent fieldwork.<ref name=":1" /><ref name="Campbelletal2016" /> This situation is further complicated since ''C. russelli'' may not even belong to the genus ''Chasmosaurus'', sharing features with the contemporaneous derived chasmosaurine ''[[Utahceratops]].''<ref>{{Cite journal|last=Fowler|first=Denver Warwick|date=2017-11-22|title=Revised geochronology, correlation, and dinosaur stratigraphic ranges of the Santonian-Maastrichtian (Late Cretaceous) formations of the Western Interior of North America|journal=PLOS ONE|language=en|volume=12|issue=11|pages=e0188426|doi=10.1371/journal.pone.0188426|issn=1932-6203|pmc=5699823|pmid=29166406|bibcode=2017PLoSO..1288426F|doi-access=free}}</ref>

Today, taxonomy of ''Chasmosaurus'' 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.<ref name=":1" /> Specimens referred to ''C. russelli'' are all from the lower Dinosaur Park Formation, stratigraphically and morphologically separate from ''C. belli.''<ref name=":1" /> 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''.<ref name=":0" /> 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''."<ref name=":1" />

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''.<ref>{{Cite journal|last1=Longrich|first1=Nicholas|title=Systematics of ''Chasmosaurus'' - new information from the Peabody Museum skull, and the use of phylogenetic analysis for dinosaur alpha taxonomy|year=2015|journal=F1000Research|volume=4|pages=1468|doi=10.12688/f1000research.7573.1|url=https://f1000research.com/articles/4-1468|doi-access=free}}</ref> 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.