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= Chasmosaurinae = Chasmosaurinae is one of two subfamilies of ceratopsid dinosaurs living in the late Cretaceous Period, and was one of the most successful groups of herbivores of its time. The group was named by Lawrence Lambe in 1915. Broadly, the most distinguishing features of Chasmosaurinae 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.

Members of this subfamily first appeared in the early Campanian, and the majority of chasmosaurine fossils that have been discovered date back to the mid and late Campanian (like Chasmosaurus and Utahceratops) or early Maastrichtian (like Triceratops and Anchiceratops). Many Chasmosaurines outlived members of the other ceratopsid subfamily, Centrosaurinae, going extinct during the Cretaceous–Paleogene extinction event, along with all other non-avian dinosaurs. Centrosaurines went extinct in the early Maastrichtian, and some evidence points to the Chasmosaurus clade of chasmosaurine ceratopsians becoming extinct at the same time.

Characters
Many features important in identifying genera within Chasmosaurinae are characters of the skull. In their characterization of several ceratopsid specimens found in the Aguja Formation, Lehman et al. maintain that "generic- and specific-level diagnoses of chasmosaurines rely almost exclusively on features of the parietal, and the epiparietals that adorn it; in particular the form, placement and number of epiparietals is generally perceived to be of utmost significance in discriminating taxa." Other important cranial characters include the orbital and nasal horncore length, the orbit shape, and the number of squamosal epoccipitals.

Chasmosaurines, like other ceratopsians, possess postorbital horns and a parietosquamosal frill, which consists of extended parietal and squamosal bones, sometimes embellished with a lining of epoccipital bone. In most ceratopsid genera, there appears to be a split between having both epoccipital frill linings and a larger nasal horncore and having a more elongated frill and bigger postorbital horns. Chasmosaurines are representative of the latter character states. The postorbital horncores are larger than the nasal horncores in all chasmosaurines except for Chasmosaurus belli, Vagaceratops, and Regaliceratops. They also have much more elaborate premaxillae with many fossae and fenestrae, unlike centrosaurine premaxillae which are generally flatter, solid, and simpler. Chasmosaurines have a subtriangular maxilla, which is very low in the primitive condition seen in chasmosaurines like Chasmosaurus and Mojoceratops, and tall in more derived chasmosaurines like Kosmoceratops and Pentaceratops. The frontal fontanelle is open between orbits in centrosaurine ceratopsids in chasmosaurines like Chasmosaurus and Pentaceratops. This is the primitive condition, and closes in more derived chasmosaurines, like Kosmoceratops, Anchiceratops, Arrhinoceratops, and Triceratopsini. The jugal bone of the skull is very thick, tapers to a point, and sometimes fuses with the epijugal; in some species, most notably Pentaceratops, this feature is so pronounced that it is referred to as either a jugal or epijugal horn. Long epijugal horns are also observed in Agujaceratops, Kosmoceratops, Utahceratops, Bravoceratops, Anchiaceratops, and Arrhinoceratops. The jugal bone is further modified in chasmosaurines more derived than Chasmosaurus such that the infratemporal process is lost.

Sexual Dimorphism
There is currently no clear consensus among members of the scientific community as to whether or not there was sexual dimorphism in Chasmosaurines. Members of the subfamily do have substantial variety in their cranial embellishments, but some argue that this variation is not significant enough between individuals of different sexes to be sexual dimorphism. In 1990, Dr. Thomas Lehman argued that all chasmosaurine genera contain at least one species that does exhibit sexual dimorphism in the positioning of postorbital horncores. He notes that there appeared to be two different "morphs" among individuals of the species Chasmosaurus mariscalensis (later re-evaluated and declared to be Agujaceratops, a new chasmosaurine genus) found in a bone bed. However, due to disarticulation of skeletal remains, there was no way to identify whether or not the two different sizes of horncores corresponded with the two sexes. Others before Lehman also believed that cranial ornamentation and frills were related to sexual dimorphism.

Classification
Below is the phylogeny of Brown et al (2015):

* SEE WIKI PAGE*

Below is the result of a phylogenetic analysis by Mallon et al. from their description of Spiclypeus shipporum. Bravoceratops and Eotriceratops were removed because it was found that they decrease resolution in their analysis because of the authors' new interpretation of epiparietal configurations. Regaliceratops was not resolved as a member of the Triceratopsini.

* SEE WIKI PAGE*

Biogeography
Ceratopsids are widely distributed across the region of North America known as Laramidia, which used to be physically separated from the other half of the continent by a body of water. A large number of chasmosaurines have been found in Western Canada, primarily in Alberta and Saskatchewan. In the United States, they have been found in Utah, Wyoming, New Mexico, and Texas. Two chasmosaurine species have been found in northern Mexico, along with several unclassified ceratopsids. A number of chasmosaurine taxa have been found across most of Laramidia, but there is still a high degree of endemism in the distribution of many other taxa. Kosmoceratops is found exclusively in southern Laramidia, Agujaceratops species have only been found in Texas in the Aguja Formation and in northern Mexico.

Social Behaviors
Ceratopsids are typically regarded as herding animals because of observed bone beds containing juvenile and adult ceratopsids of the same species. However, the majority of evidence pointing toward this is drawn from centrosaurine bone beds and applied to all other ceratopsids, including chasmosaurines. Only 6 of the 14 chasmosaurine taxa have been found in bone beds, and these are both less common and contain fewer individual specimens than bonebeds of centrosaurine taxa.

Chasmosaurines lived alongside centrosaurines, but there are significantly fewer chasmosaurine bone beds than centrosaurine bone beds. This may indicate less herding and breeding group behaviors in chasmosaurines, but could also be the result of bad preservation. The existing bone beds could alternatively be interpreted as evidence of herding behavior because there are no preserved clues indicative that environmental stresses rather than social behaviors led to the formation of these groups.