The skull had a beak and shearing cheek teeth arranged in continuous dental batteries, suggesting that the animal sliced up plants.

[5] Barnum Brown and crew, working for the American Museum of Natural History in New York, collected a nearly complete articulated skeleton with a partial skull in 1915.

[5][7] In the summer of 2006, Darren Tanke of the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta relocated the long lost S. parksi site.

S. sphenocerus, described by Edward Drinker Cope in 1890 as a species of Monoclonius and based on a nasal bone with a broken Styracosaurus-like straight nose horn, was attributed to Styracosaurus in 1915.

[9] "S. makeli", mentioned informally by amateur paleontologists Stephen and Sylvia Czerkas in 1990 in a caption to an illustration, is an early name for Einiosaurus.

[11] A species, Styracosaurus ovatus, from the Two Medicine Formation of Montana, was described by Gilmore in 1930, named for a partial parietal under the accession number USNM 11869.

[12] An additional specimen from the Two Medicine Formation was referred to Styracosaurus ovatus in 2010 by Andrew McDonald and John Horner, having been found earlier in 1986 but not described until that year.

[15] Later in 2020, the supposed specimen MOR 492 was redescribed by John Wilson and colleagues, who reinterpreted its anatomy in a way that contrasted McDonald and Horner who referred it to Styracosaurus ovatus.

While Wilson et al. agreed that the close relationship between S. albertensis and S. ovatus meant that the genus name Rubeosaurus should be abandoned, they cautioned against synonymization.

MOR 492 was moved into its own taxon, Stellasaurus ancellae, which nested alongside Einiosaurus, Achelousaurus and Pachyrhinosaurus in a similar result to McDonald and Horner when the specimen was included as part of the S. ovatus hypodigm.

[4] The nasal horn was estimated by Lambe at 57 centimeters (22 inches) long in the type specimen,[19] but the tip had not been preserved.

Some individuals had small hook-like projections and knobs at the posterior margin of the frill, similar to but smaller than those in Centrosaurus.

Other members of the clade include Centrosaurus (from which the group takes its name),[21][22] Pachyrhinosaurus,[21][23] Avaceratops,[21] Einiosaurus,[23][24] Albertaceratops,[24] Achelousaurus,[23] Brachyceratops,[7] and Monoclonius,[21] although these last two are dubious.

[28][29][30] The cladogram depicted below represents a phylogenetic analysis by Chiba et al. (2017):[31] Diabloceratops eatoni Machairoceratops cronusi Avaceratops lammersi (ANSP 15800)

The discovery of Protoceratops, in 1922, shed light on early ceratopsid relationships,[32] but several decades passed before additional finds filled in more of the blanks.

Subtle changes can be traced in the arrangement of the horns through this lineage, leading from Rubeosaurus to Einiosaurus, to Achelousaurus and Pachyrhinosaurus.

However, the lineage may not be a simple, straight line, as a pachyrhinosaur-like species has been reported from the same time and place as Styracosaurus albertensis.

[8][34] The mass deaths may have been a result of otherwise non-herding animals congregating around a waterhole in a period of drought, with evidence suggesting the environment may have been seasonal and semi-arid.

[40] Dodson has proposed that Late Cretaceous ceratopsians may have knocked down angiosperm trees and then sheared off leaves and twigs.

Early in the 20th century, paleontologist R. S. Lull proposed that the frills of ceratopsian dinosaurs acted as anchor points for their jaw muscles.

[28] It was long believed that ceratopsians like Styracosaurus used their frills and horns in defence against the large predatory dinosaurs of the time.

[45] However, a newer study compared incidence rates of skull lesions in Triceratops and Centrosaurus and showed that these were consistent with Triceratops using its horns in combat and the frill being adapted as a protective structure, while lower pathology rates in Centrosaurus may indicate visual rather than physical use of cranial ornamentation, or a form of combat focused on the body rather than the head;[46] as Centrosaurus was more closely related to Styracosaurus and both genera had long nasal horns, the results for this genus would be more applicable for Styracosaurus.

A similar theory has been proposed regarding the plates of Stegosaurus,[49] although this use alone would not account for the bizarre and extravagant variation seen in different members of the Ceratopsidae.

[28][50] Evidence that visual display was important, either in courtship or in other social behavior, can be seen in the fact that horned dinosaurs differ markedly in their adornments, making each species highly distinctive.

[3] Styracosaurus is known from the Dinosaur Park Formation, and was a member of a diverse and well-documented fauna of prehistoric animals that included horned relatives such as Centrosaurus and Chasmosaurus, duckbills such as Prosaurolophus, Lambeosaurus, Gryposaurus, Corythosaurus, and Parasaurolophus, ornithomimids Struthiomimus, tyrannosaurids Gorgosaurus, and Daspletosaurus, and armored Edmontonia and Euoplocephalus.

[53] The Dinosaur Park Formation is interpreted as a low-relief setting of rivers and floodplains that became more swampy and influenced by marine conditions over time as the Western Interior Seaway transgressed westward.

[55] In the Two Medicine Formation, dinosaurs that lived alongside Styracosaurus ovatus included the basal ornithopod Orodromeus, hadrosaurids (such as Hypacrosaurus, Maiasaura, and Prosaurolophus), the centrosaurines Brachyceratops and Einiosaurus, the leptoceratopsid Cerasinops, the ankylosaurs Edmontonia and Euoplocephalus, the tyrannosaurid Daspletosaurus (which appears to have been a specialist of preying on ceratopsians), as well as the smaller theropods Bambiraptor, Chirostenotes, Troodon, and Avisaurus.