Kosmoceratops is estimated to have been 4.5 m (15 ft) long and to have weighed 1.2 t (1.3 short tons).
As a ceratopsid, it would have been a quadruped with a heavily constructed skeleton, a large pelvis, and a relatively shortened tail.
It had long main tooth rows which formed complex slicing dental batteries containing hundreds of teeth behind an edentulous (toothless) beak.
The upper premaxillary beak of Kosmoceratops was triangular, and the frontmost rostral bone was pointed, with a tip that projected forward and downward.
The nasal horncore (the bony projection from which the nose horn grew) was unusual among chasmosaurines in that it was blade-like, with a base that was elongated and narrow from side to side, and with a flattened upper portion.
The nasal horncore was quadrangular in overall shape and was placed relatively far back on the snout.
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 narial strut of the premaxilla (that extended from the bottom of the nasal cavity to the top) was also inclined hindward, a feature also seen in Anchiceratops and Arrhinoceratops, and the narial process that projected backwards and up from the premaxilla was a triangular prong.

The region around the orbits (eye sockets) was distinctive; while most chasmosaurines had supraorbital horncores (horns above the eyes) that were oriented either forward or hindward, Kosmoceratops and Utahceratops had horncores that were oriented upward and to the sides, superficially similar to those of the modern bison.
Compared to the short and blunt horncores of Utahceratops, those of Kosmoceratops were more elongated and slender, curving upward then downward, ending in pointed tips.
Right in front and in the middle of the orbits, the skull roof had a pronounced hump, which was present in few other ceratopsids, such as Diabloceratops.
As was typical for chasmosaurines other than Chasmosaurus, it had relatively large epijugal ossifications ("cheek horns").
The lateral temporal fenestrae (openings at the sides of the skull) were tall and narrow.

The parietosquamosal neck frill (formed by the parietal and squamosal bones) of Kosmoceratops was very derived (or "advanced"), sharing several features with Vagaceratops only.
This included that the frill was short from front to back, with small parietal fenestrae (openings through the frill) placed far back, and the presence of ten hook-like epiossifications (the accessory ossifications that formed the horns and lined the margins of the neck frills in ceratopsids) on the hind margin of the frill.
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.
Though chasmosaurines have traditionally been considered the "long-frilled" ceratopsids, Kosmoceratops had the shortest frill relative to its width among chasmosaurines and the smallest parietal fenestrae relative to the total area of the frill of any ceratopsid.
The squamosal bones of Kosmoceratops were strongly curved in side view, and their side margins were parallel in top view.
The parietal bones did not project past the squamosals and had V-shaped hind margins, with emargination (a series of notches) spanning their entire width.

The epiossifications on the squamosal bones of Kosmoceratops became progressively larger towards the back of the neck frill.
There were five well-developed epiossifications per side on the hind-margin of the frill: three forward-curved epiparietals (ep 1-3) on the parietal bone, one forward-curved epiparietosquamosal (esp) on the border between the parietal and squamosal bones, and one episquamosal (es1) on the squamosal bone that was directed to the side and downward.
The forward-curving epiparietals had prominent
Kosmoceratops is estimated to have been 4.5 m (15 ft) long and to have weighed 1.2 t (1.3 short tons). As a ceratopsid, it would have been a quadruped with a heavily constructed skeleton, a large pelvis, and a relatively shortened tail. It had long main tooth rows which formed complex slicing dental batteries containing hundreds of teeth behind an edentulous (toothless) beak. The upper premaxillary beak of Kosmoceratops was triangular, and the frontmost rostral bone was pointed, with a tip that projected forward and downward. The nasal horncore (the bony projection from which the nose horn grew) was unusual among chasmosaurines in that it was blade-like, with a base that was elongated and narrow from side to side, and with a flattened upper portion. The nasal horncore was quadrangular in overall shape and was placed relatively far back on the snout. 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 narial strut of the premaxilla (that extended from the bottom of the nasal cavity to the top) was also inclined hindward, a feature also seen in Anchiceratops and Arrhinoceratops, and the narial process that projected backwards and up from the premaxilla was a triangular prong.
The region around the orbits (eye sockets) was distinctive; while most chasmosaurines had supraorbital horncores (horns above the eyes) that were oriented either forward or hindward, Kosmoceratops and Utahceratops had horncores that were oriented upward and to the sides, superficially similar to those of the modern bison. Compared to the short and blunt horncores of Utahceratops, those of Kosmoceratops were more elongated and slender, curving upward then downward, ending in pointed tips. Right in front and in the middle of the orbits, the skull roof had a pronounced hump, which was present in few other ceratopsids, such as Diabloceratops. As was typical for chasmosaurines other than Chasmosaurus, it had relatively large epijugal ossifications ("cheek horns"). The lateral temporal fenestrae (openings at the sides of the skull) were tall and narrow.
The parietosquamosal neck frill (formed by the parietal and squamosal bones) of Kosmoceratops was very derived (or "advanced"), sharing several features with Vagaceratops only. This included that the frill was short from front to back, with small parietal fenestrae (openings through the frill) placed far back, and the presence of ten hook-like epiossifications (the accessory ossifications that formed the horns and lined the margins of the neck frills in ceratopsids) on the hind margin of the frill. 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. Though chasmosaurines have traditionally been considered the "long-frilled" ceratopsids, Kosmoceratops had the shortest frill relative to its width among chasmosaurines and the smallest parietal fenestrae relative to the total area of the frill of any ceratopsid. The squamosal bones of Kosmoceratops were strongly curved in side view, and their side margins were parallel in top view. The parietal bones did not project past the squamosals and had V-shaped hind margins, with emargination (a series of notches) spanning their entire width.
The epiossifications on the squamosal bones of Kosmoceratops became progressively larger towards the back of the neck frill. There were five well-developed epiossifications per side on the hind-margin of the frill: three forward-curved epiparietals (ep 1-3) on the parietal bone, one forward-curved epiparietosquamosal (esp) on the border between the parietal and squamosal bones, and one episquamosal (es1) on the squamosal bone that was directed to the side and downward. The forward-curving epiparietals had prominent
Kosmoceratops