Specimens were discovered in Utah in the Kaiparowits Formation of the Grand Staircase–Escalante National Monument in 2006 and 2007, including an adult skull and postcranial skeleton and partial subadults.

Kosmoceratops was a chasmosaurine ceratopsid and was originally suggested to be closely related to Vagaceratops (which also had forward-curving epiossifications on the back of the frill) but this has been debated, some authors finding the latter closer to Chasmosaurus.

The Kaiparowits Formation dates to the late Campanian age and was deposited on Laramidia, an island continent, when North America was divided at the center by the Western Interior Seaway.

[2] In a 2010 press release announcing the study, Sampson described Kosmoceratops as "one of the most amazing animals known, with a huge skull decorated with an assortment of bony bells and whistles", and considered GSENM "one of the country's last great, largely unexplored dinosaur boneyards".

In 2014 (and in 2015, in an article that failed peer review), the paleontologist Nicholas R. Longrich considered the skull similar to Kosmoceratops in features of the snout but differing in the shape of the naris and nasal horn.

It had long main tooth rows which formed complex slicing dental batteries containing hundreds of teeth behind an edentulous (toothless) beak.

The naris (bony nostril opening) was different from other ceratopsids in being tall, relatively narrow from front to back, and distinctly ellipse-shaped (rather than near-circular), with a pronounced hindward inclination.

The frill of Kosmoceratops was more extreme than that of Vagaceratops; its width was about double its length (measured across the surface of the bone), with the parietal fenestrae being much smaller and positioned farther back, and it had more elongated and distinct epiossifications on the hind margin.

[2][20] Two clades (groups consisting of all taxa that share a common ancestor) of ceratopsid dinosaurs—Centrosaurinae and Chasmosaurinae—are recognized based mainly on the elaborate ornamentation of their skull roofs.

In 2010, Sampson and colleagues placed Kosmoceratops in the latter group due to the premaxilla having a narial strut and a triangular process, as well as the presence of an elongated squamosal bone.

Their phylogenetic analysis found Kosmoceratops to be the sister taxon to Vagaceratops, in a clade grouped with derived chasmosaurines from the latest Campanian and Maastrichtian stages of the Late Cretaceous epoch including Triceratops, but not closely related to the more basal (or "primitive") Chasmosaurus.

Sampson and colleagues had therefore also reinterpreted the pattern of epiossifications in Vagaceratops similarly, but Campbell suggested that it had four or five epiparietals instead, therefore finding it to be the sister taxon to Chasmosaurus rather than Kosmoceratops.

While they acknowledged that some researchers had grouped Vagaceratops with Chasmosaurus instead, they found the forward-curled epiossifications at the back of the frill very distinctive, suggesting that Spiclypeus provided clues to explain the evolution of this feature.

Contrary to previous studies and informed by their new epiossification numbering system, Kosmoceratops was found to be closer to Chasmosaurus, and together with Vagaceratops, represented the most derived and youngest members of that lineage.

As they found Vagaceratops likely to be the sister taxon of Kosmoceratops, they suggested it should be maintained as a distinct genus from Chasmosaurus, as its placement would probably remain unstable until chasmosaurines are better understood.

[31] The possible functions of ceratopsian horns and frills have been debated, including fighting off predators, species recognition, and temperature control, though the dominant hypothesis involves enhancing reproductive success.

They noted that many large ceratopsians had openings in their frills, making them of little use in defense, and that the wide variety in the size and orientation of their horns did not have an obvious function in combat.

[35] In 2015, biologist Pasquale Raia and colleagues examined the evolutionary increase in the complexity and size of animal ornaments (such as crests, horns, and tusks) over time, using ammonites, deer, and ceratopsians as examples.

[39] The formation represents an alluvial to coastal plain setting that was wet, humid, and dominated by large, deep channels with stable banks and perennial wetland swamps, ponds, and lakes.

Rivers flowed generally west across the plains and drained into the Western Interior Seaway; the Gulf Coast region of the United States has been proposed as a good modern analogue (such as the current day swamplands of Louisiana).

[43] The swamps and wetlands were dominated by up to 30 m (98 ft) cypress trees, ferns, and aquatic plants including giant duckweed, water lettuce, and other floating angiosperms.

[4][2] Levitt reported that every bone of the assigned subadult or adult specimen UMNH VP 21339 appeared to have been broken before depositing, and its matrix is stacked siltstones and mudstones with minor sandstones, which suggests a pond environment.

It has been postulated that there was a latitudinal array of dinosaur "provinces" or biomes on Laramidia during the Campanian and Maastrichtian ages of the Late Cretaceous, the boundary lying around modern northern Utah and Colorado; the same major clades are known from the north and south but are distinct from each other at the genus and species levels.

They pointed out that in contrast to the Maastrichtian, the preceding Campanian stage had a better sampled, diverse, and far-ranging dinosaur assemblage, as well as more precise geographical and stratigraphical data.

[2] Sampson and colleagues stated that their study was the first time intracontinental endemism within dinosaurs was documented (with distinct chasmosaurine taxa co-occurring north and south on Laramidia).

After the barrier dissolved around 75.7 million years ago, the Kosmoceratops lineage (represented by Vagaceratops) that had been restricted to southern Laramidia dispersed to the north, giving rise to all later chasmosaurines, such as Anchiceratops and Triceratops.

Possible physical barriers to dispersal include an unidentified mountain range from east to west, flooding in the plain regions by the Western Interior Seaway (which would have temporarily eliminated low-elevation habitats in central Laramidia), or a major river system.

Gates and colleagues suggested that the increase in North American dinosaur biodiversity during the Campanian was due to orogenic events (which lead to changes in the Earth's crust where continental plates meet) in the Western Interior Basin, including the incipient confluence of the Sevier Orogenic Belt and plate tectonics on Laramidia, which formed mountains that isolated ceratopsids and hadrosaurids and led to their diversification.

[17] The same year, Mallon and colleagues found P. aquilonius to be an invalid nomen dubium (dubious name) and agreed that there had been a dispersal barrier between north and south Laramidia.

For example, they pointed out that contrary to the claim made by Sampson and colleagues, Kosmoceratops and Utahceratops were not contemporaneous with Vagaceratops (which was younger) and all were older than Pentaceratops.