Breviceratops: a small horned dinosaur known from young skulls

Breviceratops kozlowskii is a small protoceratopsid from the Late Cretaceous of Mongolia. Its best-known fossils are two juvenile skulls from Khulsan, one accompanied by parts of a skeleton. The young age of both animals is central to the history of the name: some researchers considered them immature individuals of another genus, while a later revision retained Breviceratops as a distinct taxon based on a combination of anatomical characters.

Quick facts

From a species of Protoceratops to its own genus

Teresa Maryańska and Halszka Osmólska described the fossils in 1975 as ?Protoceratops kozlowskii. The question mark signalled uncertainty about the original assignment. The holotype, ZPAL MgD-I/117, includes a skull missing the very front of the snout and associated portions of the vertebral column, ribs, pelvis and limbs. A second specimen, ZPAL MgD-I/116, is a smaller, crushed skull. Both were collected at Khulsan in the Gobi and are associated with the Baruungoyot Formation.

In 1990, Sergei Kurzanov erected the genus Breviceratops. The name combines a Latin root meaning “short” with a Greek-derived term for a horned face. The species honours the Polish palaeontologist Roman Kozłowski. Later, Kurzanov transferred additional Mongolian fossils to Bagaceratops rozhdestvenskyi. Because those referrals blurred the boundary between the two names, some accounts proposed that the original Breviceratops skulls might also belong to young Bagaceratops.

The name history also reflects a practical problem in the Khulsan collection: many small ceratopsian bones are incomplete, and young individuals can share proportions that differ from adults. A fossil found at the same locality is not automatically part of the same species. The 2019 reassessment compared the diagnostic parts specimen by specimen and treated poorly preserved or non-distinctive material cautiously, rather than using geographic proximity to enlarge the sample.

Łukasz Czepiński’s 2019 revision retained Breviceratops kozlowskii as a valid species. The conclusion rested on a combination of skull and jaw details, not on small body size alone. The revision also narrowed the material that could confidently be assigned to each species. A taxon can therefore remain valid even when the list of fossils attributed to it becomes shorter.

A diagnostic mix of skull features

The known skulls preserve teeth in the premaxilla at the front of the upper jaw. Among protoceratopsids, this condition is also seen in Protoceratops andrewsi. The lower jaw lacks the sharp V-shaped buccal ridge described in Bagaceratops. At the same time, Breviceratops has a small additional opening in front of the orbit, a derived feature shared with Bagaceratops. This mosaic makes the diagnosis a comparison of several structures rather than a single dramatic horn or crest.

The front of the snout is incomplete in the holotype, so the shape of the nasal region cannot be fully assessed. The two skulls also differ in size because they belonged to growing animals. Ceratopsian skulls changed as individuals matured: the proportions of the frill, the texture of the bones and the contacts between skull elements could all develop with age. Neither specimen gives a reliable template for the adult head.

Body, diet and the limits of reconstruction

The partial skeleton shows a four-legged ceratopsian with a beak, rows of cheek teeth and a bony frill behind the skull. It does not preserve a complete adult body. Published estimates that give an exact adult length or mass would require scaling the juveniles against other animals and should not be mistaken for direct measurements. The mature form of the frill and any nasal boss remain uncertain.

The beak and cheek teeth support a plant-eating interpretation. They do not reveal which plants were eaten, how high the animal browsed or whether it lived in groups. No stomach contents, associated coprolites, nests or trackways have been reported for this species. Its known anatomy can be compared with other horned dinosaurs in the dinosaur catalogue, including the more complete Protoceratops and the related Bagaceratops.

Khulsan and the Gobi record

Khulsan lies in the Gobi Desert, where the Baruungoyot Formation preserves a Late Cretaceous terrestrial ecosystem. Formation-level age assignments are broad and do not provide an exact date for either skull. Fossils from the wider unit include dinosaurs, lizards, mammals and eggs, but occurrence in the same formation does not prove that individual animals met or shared a specific habitat patch.

No skin, pigment-bearing structures or complete adult skeleton are known for Breviceratops. A reconstruction can reasonably use the general body plan of protoceratopsids, but its colours, soft tissues and mature ornament are artistic choices. The fossils are most informative as a record of juvenile anatomy and as a case study in how growth can complicate species identification.