Regaliceratops: a crown-shaped frill and a test of convergence

Regaliceratops peterhewsi is a useful reminder that a dinosaur’s visual resemblance can mislead evolutionary classification. Its skull has a prominent nasal horn and a crown-like outline of frill projections that recall some centrosaurines. Yet the original analysis placed Regaliceratops among chasmosaurines. The proposed explanation is convergence: similar ornament patterns evolved in separate lineages, rather than being inherited from a recent shared ancestor.

Quick facts

A skull found along the Oldman River

Geologist Peter Hews discovered the specimen in 2005 in a cliff beside the Oldman River in Alberta. The skull was excavated in later field seasons and prepared at the Royal Tyrrell Museum. Caleb Brown and Donald Henderson named Regaliceratops peterhewsi in 2015. The genus name evokes a royal or crown-like face and the museum’s name; the species honours Hews. The holotype is catalogued as TMP 2005.055.0001.

The specimen preserves most of the skull but is compressed and incomplete, including a missing snout tip. Its sedimentary context was assigned to the upper St. Mary River Formation in the original study, with age interpreted as Maastrichtian. The precise formation correlations and regional stage boundaries are geological conclusions; the skull itself cannot supply a calendar date. Its deformation also means some dimensions and spatial relationships need reconstruction.

A distinctive pattern of cranial ornaments

The preserved skull has a large nasal horn core, relatively small brow horn cores and substantial bony projections along the frill. The overall arrangement produces the crown-like silhouette that inspired the name. These are direct anatomical features. The soft covering of each horn and the external outline of the living frill are unknown, so illustrations extrapolate from bone and comparison with other ceratopsids.

Brown and Henderson compared this ornament pattern with the better-known divisions of Ceratopsidae. Regaliceratops looked unusual within the chasmosaurines, while several features recalled centrosaurines. Their phylogenetic analysis nonetheless placed it with chasmosaurines. The resulting mismatch between tree position and appearance motivated the convergence interpretation. This is a testable evolutionary explanation based on comparative anatomy, not proof of the exact selective pressure that produced each horn.

Convergence and the limits of a single skull

Convergent evolution occurs when similar features arise independently in different lineages. It can make unrelated or more distantly related animals look alike, especially when structures serve comparable roles. In Regaliceratops, the original authors argued that its horn-and-frill arrangement resembles centrosaurine ornamentation despite its inferred chasmosaurine relationships. Other analyses can revise the exact branching position as additional taxa and characters are evaluated.

The holotype represents one individual, so it cannot show the full range of variation within a population or how the skull changed through growth. A single skull also cannot reveal courtship, combat or social display directly. The fossil is strong evidence for a distinctive adult cranial anatomy; its function and developmental history need independent evidence. A hypothesis about signalling may be plausible without being confirmed by the shape alone.

What the fossil does not preserve

No complete skeleton is known for the named species, so body proportions and size are estimated from skull dimensions and comparisons with other ceratopsids. The fossil does not preserve colour, skin, a keratin sheath or stomach contents. Broad herbivory is consistent with ceratopsid anatomy, but an exact diet or feeding height cannot be read from this skull. These limits are easy to lose when the striking frill dominates an illustration.

Regaliceratops is therefore especially useful for separating three questions: what its skull looked like, where it may sit on the ceratopsid tree, and why its ornaments took that form. The first is observed directly; the second is a phylogenetic inference; the third remains functional interpretation. Compare its profile with other named horned dinosaurs in the dinosaur catalogue to see how shared family membership can coexist with markedly different ornament shapes.

A specimen shaped by preservation

The skull was embedded in well-cemented sediment and is compressed, with some surfaces obscured by matrix. Preparation and reconstruction make its anatomy accessible, but they cannot restore every missing boundary with equal confidence. Where elements are displaced or deformed, researchers must distinguish the shape of the fossil as preserved from the estimated position before burial. This matters especially for a skull whose diagnosis depends on the arrangement of horns and frill structures.

The excavation and preparation history also explains why the specimen received detailed attention: a large skull in hard rock required careful removal and extended laboratory work. Those practical facts do not change the taxonomy, but they help explain how a fossil becomes a study specimen. Its museum catalogue number links published descriptions to the actual object, allowing future researchers to remeasure the bones or test a different interpretation against the same evidence.