Ajkaceratops

Ajkaceratops; Temporal range: Santonian; ~85 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Holotype proposed rostral fused with premaxillae
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Neornithischia
Clade:	†Ceratopsia
Genus:	†Ajkaceratops; Ősi et al., 2010
Species:	†A. kozmai
Binomial name
	†Ajkaceratops kozmai; Ősi et al., 2010

Ajkaceratops (pronounced "oi-ka-sera-tops") is a genus of ornithischian dinosaur described in 2010. It lived during the Late Cretaceous in the western Tethyan archipelago, in what is now Europe. The type species, A. kozmai,^[1] was originally described as a ceratopsian most closely related to forms in east Asia, from where its ancestors may have migrated by island-hopping. Later research however has questioned this assignment, and treats Ajkaceratops as an ornithischian of unresolved affinity.

Discovery

The holotype, cataloged as MTM V2009.192.1, consists only of a few skull fragments, including snout with proposed rostral bone, fused premaxillae, and maxillae fragments (beak and jaw fragments). These fossils are kept in the Hungarian Natural History Museum, in Budapest. The generic name, Ajkaceratops, honors Ajka, a town in Hungary where the fossils were first discovered, combined with the given greek nomination ceratops, meaning "horned face". The specific name, "kozmai", honors Károly Kozma.^[1]

Description

Although the fossils are fragmentary, the paper describing Ajkaceratops estimated a body length of 1 m (3.3 ft).^[1] Other material includes four predentary bones, cataloged as MTM V2009.193.1, V2009.194.1, V2009.195.1, and V2009.196.1; these are also believed to have belonged to Ajkaceratops, although they are proportionately smaller, and probably came from other individuals of the genus.^[1]

Classification

When first described, the fossils were stated to most closely resemble those of the Asian protoceratopsid Bagaceratops. Those similarities indicate Ajkaceratops is a ceratopsian related to the protoceratopsids, but more primitive than the Zuniceratops and the Ceratopsidae.^[1]

However, more recent research has questioned this referral. The proposed rostral bone of Ajkaceratops differs markedly from the rostral morphology of other ceratopsians, possessing a sub-circular cross section, pitted texture instead of grooves, and a lack of lateral slicing edges. Furthermore, the proposed rostral bone appears to have fully fused with the premaxilla, a feature that is only seen in the ontogenetically oldest members of derived ceratopsids. This has cast doubt as to whether Ajkaceratops possesses a rostral bone in the first place, a defining feature of the ceratopsian group, and instead the hooked beak represents a highly derived, hypertrophied premaxilla. While there is the possibility Ajkaceratops is a highly unique ceratopsian, it is currently referred to as an enigmatic ornithischian of uncertain affinities.^[2]

Palaeoenvironment

The fossils of Ajkaceratops were discovered in the Csehbánya Formation, which is interpreted as a floodplain and channel deposit formed by variegated clay, silt with interbedded grey and brown sand, and sandstone beds. This strata dates to the Santonian stage, around 86 to 84 million years ago. Ajkaceratops shared its environment with other dinosaurs such as Mochlodon, the nodosaurid ankylosaurs, other non-avian theropods and enantiornithine birds, as well as eusuchian crocodiles, azhdarchid pterosaurs, bothremydid turtles and teiid lizards.^[3]

References

^ ^a ^b ^c ^d ^e Ősi, Attila; Butler, R.J.; Weishampel, David B. (2010-05-27). "A Late Cretaceous ceratopsian dinosaur from Europe with Asian affinities". Nature. 465 (7297): 466–468. Bibcode:2010Natur.465..466O. doi:10.1038/nature09019. PMID 20505726. S2CID 205220451.
^ Czepiński, Łukasz; Madzia, Daniel (2024). "Osteology, phylogenetic affinities, and palaeobiogeographic significance of the bizarre ornithischian dinosaur Ajkaceratops kozmai from the Late Cretaceous European archipelago". Zoological Journal. doi:10.1093/zoolinnean/zlae048.
^ Ősi, Attila; Butler, R.J.; Weishampel, David B. (2010-05-27). "A Late Cretaceous ceratopsian dinosaur from Europe with Asian affinities (supplementary data)" (PDF). Nature. 465 (7297): 466–468. doi:10.1038/nature09019. PMID 20505726. S2CID 205220451. Retrieved 2010-05-29.