Chasmosaurines Temporal range:Late Cretaceous,78–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Chasmosaurus belli skeleton,Royal Tyrrell Museum of Palaeontology
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Ceratopsia
Family:	†Ceratopsidae
Subfamily:	†Chasmosaurinae Lambe,1915
Type species
†Chasmosaurus belli Lambe,1902
Subgroups
†Agujaceratops †Anchiceratops †Arrhinoceratops †Bisticeratops †Bravoceratops †Chasmosaurus †Coahuilaceratops †Judiceratops †Kosmoceratops †Mercuriceratops †Navajoceratops †Pentaceratops †Sierraceratops †Spiclypeus †Terminocavus †Titanoceratops? †Utahceratops †Vagaceratops †TriceratopsiniMarsh, 1889 †Eotriceratops †Nedoceratops †Ojoceratops †Regaliceratops †Tatankaceratops †Titanoceratops? †Torosaurus †Triceratops
Synonyms
Ceratopsinae? Marsh, 1888 sensu Abel, 1919 Eoceratopsinae Lambe, 1915

Chasmosaurinae is asubfamily ofceratopsiddinosaurs. They were one of the most successful groups ofherbivores of their time. Chasmosaurines appeared in the earlyCampanian, and became extinct, along with all other non-avian dinosaurs, during theCretaceous–Paleogene extinction event. Broadly, the most distinguishing features of chasmosaurines are prominent brow horns and long frills lacking long spines;centrosaurines generally had short brow horns and relatively shorter frills, and often had long spines projecting from their frills.^{[citation needed]}

Chasmosaurines evolved in western North America (Laramidia). They are currently known definitively from rocks in western Canada, the western United States, and northern Mexico. They were highly diverse and among the most species-rich groups of dinosaurs, with new species frequently described. This high diversity of named species is likely a result of the frill. The distinctive shape of the frill with the hornlets on its edges (epoccipitals) make it possible to recognize species from incomplete or fragmentary remains.^{[citation needed]}

Chasmosaurinae is defined officially in thePhyloCode by Daniel Madzia and colleagues in 2021 as "the largest clade containingChasmosaurus belli andTriceratops horridus, but notCentrosaurus apertus".^[1] Below is the result of aphylogenetic analysis by Mallon et al., following the traditional epiparietal homology scheme from their description ofSpiclypeus shipporum.Bravoceratops andEotriceratops were removed because it was found that they decrease resolution in the analysis because of the authors' new interpretation of epiparietal configurations.Regaliceratops was not resolved as a member of theTriceratopsini.^[2]

The findings of a phylogenetic study done by Fowler and Freedman in 2020 are given below. The authors proposed that two distinct and roughly contemporaneous lineages of chasmosaurines existed in the late Cretaceous: a northern "Chasmosaurus" lineage with a heart-shaped frill margin that flattens and curls over onto itself, and a southern "Pentaceratops" lineage with a pinched shut indentation in the heart-shaped frill margin. According to the cladogram below, the Triceratopsini may have derived from this later lineage. To improve resolution, certain species based on partial or immature remains (Bravoceratops andAgujaceratops) were excluded, as in the Mallon et al. study above. While this new study did not yield a single "Pentaceratops lineage," was not recovered by this revised analysis as they had predicted based on frill shape, the authors speculated that this may be due to some specimens included asPentaceratops sternbergii being misclassified, and possibly referable to other species pending further study. The authors also noted that some newer species included in the previous analysis by Mallon et al. (Spiclypeus,Regaliceratops, etc.) had yet to be coded into their revised dataset.^[3]

Triceratopsini was named byNicholas R. Longrich in 2011 for the description ofTitanoceratops, which he defined as "all species closer toTriceratops horridus than toAnchiceratops ornatus orArrhinoceratops brachyops". Triceratopsins were the largest of the chasmosaurines; suggesting that gigantism had evolved in the Ceratopsidae once. In addition there is an evolutionary trend in the solidification of the frills, the most extreme being inTriceratops.^[4]

• Timeline of ceratopsian research

• 1.https://www.paleodb.org

Wikispecies has information related toChasmosaurinae.

• Chasmosaurinae
• Dinosaur subfamilies
• Late Cretaceous dinosaurs
• Dinosaurs of North America

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