A Hidden Diversity of Misidentified Ceratopsians in Late Cretaceous Europe

Late Cretaceous Europe looked very different from the continent we know today. Rising seas fragmented the land into numerous islands of varying sizes, forming an extensive archipelago. Prolonged geographic isolation helped shape distinctive dinosaur communities, in which some relict lineages persisted while certain species underwent insular dwarfism. Yet one conspicuous gap remained. Ceratopsians (Ceratopsia) were diverse and widespread in contemporary Asia and North America, whereas Europe had yielded almost no fossils that could be confidently assigned to the group.

Europe was not entirely devoid of putative ceratopsian remains. Fragmentary teeth from Belgium and Sweden had been interpreted as belonging to ceratopsians, and the Early Cretaceous German dinosaur Stenopelix valdensis has been recovered within Ceratopsia in some phylogenetic analyses. All of these records, however, are highly incomplete, and their affinities have remained controversial. In 2010, Ajkaceratops kozmai from the Late Cretaceous of Hungary was described as the first definite ceratopsian from Europe. Its holotype, however, preserves only a small portion of the snout, and the presence of the rostral—a key ceratopsian feature—could not be clearly demonstrated. As a result, its identification as a ceratopsian was later questioned.

New fossil material has now changed the picture considerably. A recent study described specimen MTM 2025.1.1 from the Santonian Csehbánya Formation at Iharkút, Hungary, and identified it as Ajkaceratops kozmai. The new skull is substantially more complete than the holotype, preserving the region from the anterior tip of the snout to the vicinity of the supratemporal fenestra. The researchers used micro-computed tomography to visualize bones obscured by surrounding rock, then digitally corrected deformation of the fossil to reconstruct the skull. Because iguanodontians and ceratopsians show extensive convergence in their teeth, jaws and several cranial features, the skull was compared with those of other ceratopsians and early-diverging iguanodontians to test the true phylogenetic position of Ajkaceratops.

Skull reconstruction and comparison of the new specimen MTM 2025.1.1 of Ajkaceratops kozmai. (a) Skull of the early-diverging iguanodontian Tenontosaurus tilletti; (b) digitally retrodeformed skull of Ajkaceratops kozmai; (c) skull of the neoceratopsian Protoceratops andrewsi. Corresponding cranial elements are shown in the same colours in all three skulls. (d–i) Details of the skull of Ajkaceratops kozmai: (d) fused premaxillae and possible rostrals in left lateral view; (e) anterior part of the snout, with internal vascular spaces shown in red; (f) left maxilla in lateral view; (g) maxillary tooth crown in labial view; (h) left jugal in lateral view; (i) skull roof in dorsal view. Abbreviations: adp, anterodorsal process of the premaxilla; alv, alveoli; cing, cingulum; en, external naris; mp, maxillary process of the jugal; orb, orbital margin; plp, posterolateral process of the premaxilla; pmp, premaxillary process of the maxilla; pop, postorbital process of the jugal; pr, primary ridge on tooth crown; sr, secondary ridges on tooth crown; stf, supratemporal fenestra; vasc, internal vascular spaces of the rostral region; vpp, vaulted premaxillary palate（Image source：Maidment SCR et al. (2026)， CC BY 4.0 ）

The snout of Ajkaceratops curves strongly downward to form a distinctive hook-like rostrum, resembling those of ceratopsians such as Archaeoceratops and Bagaceratops. The surface of the anterior snout is heavily pitted, and CT scans revealed extensive internal vascular channels. Similar features occur in the rostrals of some other ceratopsians. The researchers still found no clear suture separating the rostral from the premaxilla, but this does not exclude the presence of a rostral. In several adult ceratopsians, the rostral becomes completely fused to the premaxilla, leaving the suture indistinguishable.

Reconstruction of Archaeoceratops oshimai（Image source：Nobu Tamura， CC BY 3.0 ）

Reconstruction of Bagaceratops rozhdestvenskyi（Image source：PaleoNeolitic， CC BY 4.0 ）

Other cranial features provided additional clues. Ajkaceratops possesses a relatively large accessory fenestra between the premaxilla and maxilla, comparable to the condition in Bagaceratops, Zuniceratops and Diabloceratops. The posterior process of the frontal reaches the anteromedial margin of the supratemporal fenestra, a configuration commonly seen in many neoceratopsians but generally absent in early-diverging iguanodontians. The maxilla contains only ten alveoli, also resembling the relatively low tooth counts of some early ceratopsians. None of these characters alone is sufficient to establish its identity, but when incorporated into phylogenetic analyses, Ajkaceratops was consistently recovered within Ceratopsia across different analytical methods and morphological datasets.

Reconstruction of Zuniceratops christopheri（Image source：Connor Ashbridge， CC BY 4.0 ）

Reconstruction of Diabloceratops eatoni（Image source：Nobu Tamura， CC BY-SA 3.0 ）

Phylogenetic position of Ajkaceratops kozmai, including material originally named Mochlodon vorosi, and other taxa traditionally assigned to Rhabdodontidae. (a) Strict consensus of eight most parsimonious trees recovered from the extended implied-weighting analysis; (b) 50% majority-rule consensus tree from the Bayesian analysis allowing variable rates of morphological character change. Marginocephalia is shown in light blue, Neoceratopsia in mid-blue, and an unnamed clade containing Ceratopsidae and some traditionally recognized 'rhabdodontid' taxa in dark blue; Ornithopoda is shown in light pink and Iguanodontia in dark pink. Taxa emphasized in bold are the main focus of the study. The silhouettes on the right represent, from top to bottom, the pachycephalosaur Pachycephalosaurus, the early neoceratopsians Archaeoceratops and Protoceratops, the ceratopsid Triceratops, the ornithopod Orodromeus, and the hadrosauriform Iguanodon（Image source：Maidment SCR et al. (2026)， CC BY 4.0 ）

Iharkút had previously yielded abundant fossils assigned to the rhabdodontid Mochlodon vorosi, which had been regarded as an early-diverging iguanodontian. Fossils of Ajkaceratops and Mochlodon occur within the same approximately 30-cm-thick breccia layer, interpreted as the product of a flash-flood event. Teeth preserved in MTM 2025.1.1 revealed that the maxillary teeth of Ajkaceratops are identical to one of the tooth morphotypes previously attributed to Mochlodon vorosi.

The lower jaw provided a second line of evidence. One feature previously regarded as distinctive of Ajkaceratops is a dorsally projecting, rounded vertical wall on the anterior part of the dentary. Strikingly, an almost identical structure is present on the holotype dentary of Mochlodon vorosi, where it had likewise been regarded as an autapomorphy of that taxon. Fossils that had been assigned to two different dinosaur lineages therefore appear to represent the same animal. The researchers consequently treated Mochlodon vorosi as a junior synonym of Ajkaceratops kozmai.

This result also prompted a reassessment of other dinosaurs traditionally classified as rhabdodontids. The Maastrichtian Romanian species Zalmoxes shqiperorum, formerly placed in the genus Zalmoxes, was given the new generic name Ferenceratops, becoming Ferenceratops shqiperorum, and was recovered within Ceratopsia.

Reconstruction of Ferenceratops shqiperorum（Image source：Connor Ashbridge， CC BY 4.0 ）

This does not mean that all dinosaurs previously classified as rhabdodontids have now been reassigned to Ceratopsia. Two relatively complete skeletons from the Aix-en-Provence region of France had previously been referred to Rhabdodon. Because the taxonomy of Rhabdodon itself still requires revision, the researchers provisionally referred to this material as the Aix 'Rhabdodon'. In the phylogenetic analyses, the Aix 'Rhabdodon' remained close to early-diverging iguanodontians. The position of Zalmoxes robustus also remains unresolved. Several parsimony analyses recovered it within Ornithopoda, whereas the Bayesian analyses placed it within Ceratopsia alongside Ajkaceratops and Ferenceratops. The current evidence therefore suggests that fossils historically grouped together as rhabdodontids may actually include members of different evolutionary lineages. Determining how much additional material requires reclassification will depend heavily on the discovery of specimens preserving associated cranial and postcranial remains.

There is an important reason why these dinosaurs could remain misidentified for so long. Ceratopsians and iguanodontians independently evolved complex chewing mechanisms, relatively large body size and quadrupedality, resulting in extensive convergence in the anatomy of the teeth, jaws, limbs and pelvis. Teeth are particularly problematic because many individual dental characters occur in both groups. The situation is further complicated by the fact that many European specimens come from bone beds, where skeletal remains from different animals can become mixed. Classifications based on isolated teeth or individual limb bones can therefore inadvertently combine material from entirely different dinosaurs.

The reinterpretation of Ajkaceratops and Ferenceratops also changes the palaeobiogeographic picture of Late Cretaceous Europe. Ceratopsians have long been known to have flourished in Asia and North America, with multiple dispersal events occurring between the two regions. Europe had appeared to be a major gap in their distribution, but at least part of that gap may have resulted from taxonomic misidentification. The new study suggests that ceratopsians did disperse into the European archipelago and subsequently diversified there into endemic lineages. These European forms may also have lacked the elaborate frills and prominent horns characteristic of North American ceratopsids, making them less immediately recognizable as typical horned dinosaurs.

If the phylogenetic relationships recovered in these analyses are supported by additional fossils, Europe may also prove to have played a role in the early dispersal history of ceratopsians between Asia and North America. The ceratopsians that once seemed to be missing from the European fossil record may never have been absent at all. Their bones had already been excavated—they had simply spent more than a century hidden under the wrong taxonomic names.

Author: Shui-Ye You

References:

1. Maidment SCR et al. (2026). A hidden diversity of ceratopsian dinosaurs in Late Cretaceous Europe. Nature.

2. Maidment SCR et al. (2026). A hidden diversity of ceratopsian dinosaurs in Late Cretaceous Europe. University of Birmingham.