Diabloceratops: an early centrosaurine with curved frill spikes

Diabloceratops eatoni was a horned dinosaur from southern Utah in the early part of the Campanian, around 81.4–81.0 million years ago. Its name refers to two long, curved spikes at the back of the frill. The genus is known securely from one adult skull, with most of the skeleton still unknown.

Its skull combines a short, deep snout, brow horns and a pair of large rear spikes. Those features once encouraged comparisons with long-frilled chasmosaurines, but the available anatomy usually places it among early centrosaurines. The dinosaur catalogue lists Diabloceratops as an individual genus alongside other ceratopsids.

Quick facts

Evidence guide

Name and discovery

The genus name combines Spanish diablo, “devil”, with ceratops, “horned face”. It refers to the pair of long spikes rising from the rear of the frill. The species name eatoni honours palaeontologist Jeffrey G. Eaton, whose work helped develop vertebrate palaeontology in southern Utah.

Joshua Smith found a partial skull near Nipple Butte in 1998. It was collected in 2000 as UMNH VP 16704. The specimen preserves a long brow-horn core but lacks the front of the snout and rear of the frill, so it cannot be identified with certainty as Diabloceratops.

The more diagnostic skull was found by Donald DeBlieux in 2002 near Last Chance Creek. It was embedded in hard sandstone. Field crews removed the block over several seasons and helicoptered it out in 2005. Preparation took more than 800 hours. James Kirkland and Donald DeBlieux described the holotype, UMNH VP 16699, in 2010 as a new genus and species.

Geological age and the Wahweap Formation

The original description placed Diabloceratops at about 79.6 million years old, which is why older summaries often give an age near 79.5–80 million years. Later high-precision dating of volcanic ash layers and a revised stratigraphic framework for the Wahweap Formation moved the type horizon earlier. Current estimates place it around 81.42–81.01 million years ago, with a central estimate near 81.27 million years.

The holotype came from the Reynolds Point Member in southern Utah. The revised age places it in the early Campanian of the Late Cretaceous. Older papers sometimes call the interval middle Campanian because they used a different stratigraphic model. When dates are compared, the underlying method and formation scheme matter.

During this time, the Western Interior Seaway divided North America. Diabloceratops lived on Laramidia, the western landmass. Wahweap sediments record rivers, floodplains, lakes and wetland settings. The formation contains many vertebrates, but fossils from a broad rock unit did not all live at precisely the same moment.

Classification and relationships

Diabloceratops is an ornithischian ceratopsian in Ceratopsidae and is usually classified within Centrosaurinae. Centrosaurines include Centrosaurus, Styracosaurus, Pachyrhinosaurus and related forms. Several analyses place Diabloceratops near the base of that subfamily. Other studies have placed it just outside Ceratopsidae, but that result is less commonly recovered in later work.

The long brow horns can make the skull appear chasmosaurine, like Triceratops. Yet classification relies on multiple characters. The squamosal bone at the side of the frill, the region around the external nostril and other skull details support a centrosaurine relationship. Early centrosaurines may have retained substantial brow horns before many later members reduced them while enlarging the nasal ornament.

Some phylogenetic analyses group Diabloceratops near Albertaceratops; others place it beside Machairoceratops or another early branch. The incomplete body and unusual skull character combination leave its exact position unsettled. It is safer to call it an early centrosaurine than to claim one undisputed closest relative.

Fossils and anatomy

The adult holotype preserves the left side of the skull and the midline, together with parts of the right side. Erosion removed the right squamosal, part of one brow horn, the jugal and a section of the maxilla. Most remaining bones are only slightly deformed. Fused sutures and growth-related ornament indicate an adult animal.

From the beak to the back of the frill, the skull measured about one metre. The long paired spikes extended its overall length by roughly another half metre. A rib and part of the lower jaw were found nearby, but they do not amount to a diagnostic body skeleton. There is no secure vertebral column, limb set or pelvis that can be assigned to the genus.

The second specimen, UMNH VP 16704, comes from Nipple Butte. Its long brow horn and a possible cheek spike led researchers to compare it with Diabloceratops. The form of its squamosal and the arrangement of frill-edge bones may point to a different centrosaurine. The species is therefore securely known from one skull, not two equivalent specimens.

The skull had a particularly short, deep snout compared with many centrosaurines. A low conical nasal ornament sat above the snout. A small additional ossification was described near it, but popular art sometimes enlarges this into a second prominent nose horn. The preserved structure was much smaller than the main ornament.

Thick brow-horn cores rose about 25 centimetres above the orbits. They angled forward and curved slightly upward. Between them, fused frontal bones formed a high, steep brow. Large epijugals on the cheeks projected outward and likely carried keratin in life, though the external sheath is not preserved.

The frill rose steeply and was broad near its base, narrowing toward the rear. Two large openings in the bone would have been covered by soft tissue. The marginal ossifications became smaller toward the rear edge. Two massive parietal spikes projected backward and then curved outward, separated by a notch in the midline. Vascular grooves on their surfaces indicate keratin sheaths, but their exact length, colour and shape cannot be recovered from the bone alone.

Size and movement

Length estimates of about four to five metres and mass estimates around one to two tonnes are based on comparison with better-known centrosaurines. They are not direct measurements of an intact Diabloceratops skeleton. A frequently repeated point estimate such as 4.5 metres or 1.3 tonnes gives a false impression of certainty. The fossil supports a substantial horned dinosaur, but the range could be wider.

It was likely a robust quadruped with a deep trunk, strong limbs and a short neck. That body plan is typical of ceratopsids, but Diabloceratops's own shoulders, pelvis and legs are unknown. Its size relative to adult Triceratops was probably smaller, yet the comparison remains indirect.

Feeding, habitat and possible behaviour

A beak at the front of the jaws could crop plants, while rows of cheek teeth formed replacement batteries that processed vegetation. The holotype's upper jaw has 24 tooth positions at different stages of growth and replacement. This is consistent with the slicing action of ceratopsid teeth. No stomach contents, associated coprolites or plants with a uniquely attributable bite are known, so the exact diet cannot be specified.

The animal likely fed on low or mid-height vegetation. That inference follows from its body plan and comparisons with other ceratopsids, not a preserved feeding trace. The nearby landscape included river channels, floodplains, lakes and wetlands under a warm climate with seasonal variation. Plants included flowering plants, conifers and ferns, though the presence of a plant in the formation does not prove it was eaten by this genus.

The horns and frill could have contributed to display, recognition, competition or defence. These functions can overlap. The outline of the head would also have been altered by keratin and skin, neither of which is preserved. One unusual opening in a frill bone was once discussed as an injury, but similar features in ceratopsids do not always result from trauma. The missing opposite side of the skull makes it difficult to test symmetry.

No Diabloceratops bonebed, nest, clutch or trackway demonstrates herd behaviour, parental care, migration or regular combat. A nearby predator fossil does not establish a direct encounter. Such scenes may be plausible reconstructions, but they remain hypotheses rather than observations about this species.

Outdated claims and remaining questions

The old age of about 79.5 million years reflects an earlier geological framework. Current dating makes the holotype closer to 81.3 million years old. Diabloceratops is among the earliest well-dated centrosaurines, though Menefeeceratops from New Mexico is also sometimes proposed as an early member and its age is less tightly constrained. Calling Diabloceratops the indisputable oldest centrosaurine goes beyond the evidence.

Likewise, its long brow horns do not make it a chasmosaurine, and its isolated skull should not be used to claim a precise whole-body measurement. A new associated skeleton would resolve more about limb proportions, mass and locomotion. Additional skulls could show whether the unusual frill traits varied within the species.

Diabloceratops remains distinctive because its skull combines a deep short snout, prominent brow horns and two long frill spikes. The fossil is strong evidence for that combination and for an early centrosaurine from Utah. Its full silhouette, behaviour, exact mass and keratin ornament are still inferred. For comparisons with other named dinosaurs, see the dinosaur catalogue.