Archaeoceratops cranium redescribed

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Yan-Chao Wang, Qian-Nan Zhang & Hai-Lu You (2025)
Cranial osteology of Archaeoceratops oshimai (Ornithischia: Ceratopsia) and phylogenetic evaluation of basal Ceratopsia
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2025.2568096
https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2568096


Archaeoceratops oshimai Dong & Azuma, 1997, is a representative early-diverging neoceratopsian dinosaur excavated from the Lower Cretaceous Xinminpu Group in the Mazongshan area of Gansu Province, China. As one of the basal members, it plays a critical role in understanding the origin and early evolution of horned dinosaurs. Here, we present a detailed redescription of its cranium based on a firsthand examination of the holotype, providing additional measurements and updated anatomical observations. Ten autapomorphic features have been identified, further solidifying the taxonomic validity of A. oshimai. Using a data matrix comprising 41 taxa and 371 characters, we re-evaluate the evolutionary relationships within Ceratopsia. Our phylogenetic analysis supports Psittacosauridae as the most basal ceratopsian and the sister clade of Neoceratopsia; ‘Chaoyangsauridae’ is not recovered as a monophyletic group, while members of ‘Chaoyangsauridae’ could form a monophyletic group with other neoceratopsians; Mosaiceratops is placed in the most basal position among non-chaoyangsauridae neoceratopsians, although it first appeared in the Late Cretaceous; A. oshimai is resolved within Neoceratopsia, closely related to other basal forms such as Auroraceratops and Liaoceratops. This study enhances our understanding of ceratopsian phylogeny and highlights the importance of thorough anatomical redescriptions for clarifying evolutionary patterns among early ornithischian dinosaurs.

[Indy Storvick]

Please do correct me if I am wrong, as I'm no expert by any stretch of the imagination, but a few of the claims in the abstract are just plain wrong based off of the phylogenetic analysis given in the supplementary information. In the given analysis, Psittacosauridae isn't sister to Neoceratopsia, that honor being taken by the polytomy of Chaoyangsauridae (more on that momentarily) and 3 other basal ceratopsians (Stenopelix, Hualianceratops, and Yinlong, the latter two being former members of Chaoyangsauridae). Additionally, Chaoyangsauridae isn't paryphyletic, nor does it nor any former member belong to Neoceratopsia. Assuming I have my definitions right (I'm taking them from Madzia et al. 2021), Neoceratopsia is defined as "max ∇ (Triceratops horridus ~ Chaoyangsaurus youngi & Psittacosaurus mongoliensis)" and Chaoyangsauridae as "max ∇ (Chaoyangsaurus youngi ~ Psittacosaurus mongoliensis & Triceratops horridus". Chaoyangsauridae should still be valid (although only having two members [Chaoyangsaurus & Xuanhuaceratops] instead of the traditional four), and it, along with Stenopelix, Hualianceratops, and Yinlong, should properly said to be recovered as basal ceratopsians rather than neoceratopsians. Am I just being overly pedantic about clade definitions, or have I made some other error? Here's the link to the analysis of which I speak if anyone has the time to correct me. 

https://figshare.com/articles/journal_contribution/Cranial_osteology_of_i_Archaeoceratops_oshimai_i_Ornithischia_Ceratopsia_and_phylogenetic_evaluation_of_basal_Ceratopsia/30281261?file=58498832

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[Mickey Mortimer]

I had the same thoughts. The authors are inconsistent in their concept of Neoceratopsia, in the same paragraph saying both "a monophyletic clade comprising Chaoyangsauridae + Neoceratopsia" and "the lowest position of the non-chaoyangsauridae neoceratopsians." Technically, probably because they didn't prune Stenopelix a posteriori, the strict consensus doesn't indicate if Xuanhuasaurus or Stenopelix are neoceratopsians or chaoyangsaurids, or outside both clades. In their "Stratigraphic congruent time-calibrated MPT with best RCI for Ceratopsia", Xuanhuasaurus is a chaoyangsaurid and Stenopelix is a neoceratopsian. Chaoyangsaurids, or a chaoyangsaurid-psittacosaurid clade, will by definition always be the sister taxon to Neoceratopsia. 

Mickey Mortimer