Ontogeny and variation of a protoceratopsid dinosaur Bagaceratops rozhdestvenskyi from the Late Cretaceous of the Gobi Desert

ABSTRACT

Bagaceratops rozhdestvenskyi is a ceratopsian dinosaur from the Late Cretaceous Baruungoyot Formation of the Gobi Desert, closely related to Protoceratops spp. Several Bag. rozhdestvenskyi skulls demonstrate a wide range of variation in their morphology and size. Here I argue that the observed variability is most likely of intraspecific nature. Specimens classified in a few allegedly distinct species from the same or near-contemporary sediments, namely Gobiceratops minutus, Lamaceratops tereschenkoi and Platyceratops tatarinovi from Baruungoyot Formation, and Magnirostris dodsoni from Bayan Mandahu, are younger subjective synonyms of Bag. rozhdestvenskyi. They plausibly represent an ontogenetic series within the latter. Breviceratops kozlowskiiis a distinct taxon. The evolutionary relationships within Protoceratopsidae are complicated by the mosaic distribution of plesiomorphic and derived features in distinct species. I suggest that taxa distribution and observed changes in morphology are an evidence for the ancestral position of Protoceratops andrewsi among protoceratopsids. It implies possible temporary separation between the geological formations of the Gobi Desert yielding distinct protoceratopsid species. The novel evolutionary scenario suggests number of convergences that occurred in Protoceratopsidae and Ceratopsoidea (reduction of the premaxillary dentition, fusion of nasals, development of the accessory antorbital fenestra). Present study reveals the significance of the intraspecific and ontogenetic variation in the study of the neoceratopsian taxonomy.

KEYWORDS:

• Dinosauria
• Ceratopsia
• Protoceratopsidae
• Mongolia
• intraspecific variation
• ontogeny

Acknowledgments

I thank Andrew Farke, Peter Makovicky, Lukas Panzarin, Eric Morschhauser, Mark Loewen, Dave Hone and Andrew Knapp for their valuable discussions and help in obtaining the important literature and illustrations of some specimens. I thank my supervisor Jerzy Dzik, two anonymous reviewers, and my colleagues, Mateusz Tałanda, Tomasz Szczygielski, Andrzej Wolniewicz, Dawid Mazurek, and Daniel Madzia for their helpful suggestions that improved my manuscript. Robert Bronowicz, Tomasz Singer, Mototaka Saneyoshi, Phillip Currie, Robin Sissons, Frank Varriale, Ali Nabavizadeh and Ji Shu’an kindly provided illustrations and details of some specimens.

I am grateful for Khishigjav Tsogtbaatar and Ulziitseren Sanjaadash (Institute of Paleontology and Geology, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia), Vladimir Alifanov, Victor Tereschenko and Andrey Sennikov (Institute of Paleontology, Russian Academy of Science, Moscow, Russia), You Hailu, Xing Xu, Zhang Qiannan and Wang Yaming (Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China), Jolanta Kobylińska, Tomasz Sulej, Krzysztof Owocki and Justyna Słowiak (Institute of Paleobiology, Polish Academy of Sciences, Warsaw, Poland), Mark Norell and Carl Mehling (American Museum of Natural History, New York, NY, USA), Mark Loewen and Carrie Levitt-Bussian (Natural History Museum of Utah, Salt Lake City, UT, USA), Gavin McCullough and Robert McCord (Arizona Museum of Natural History, Mesa, AZ, USA), Amanda Millhouse (Smithsonian Institution National Museum of Natural History, Washington, DC, USA), Pascal Godefroit and Annelise Folie (Royal Belgian Institute of Natural Sciences, Brussels, Belgium), and Attila Ősi, Mihály Gasparik and Réka Kalmár (Hungarian Natural History Museum, Budapest, Hungary) for help during my visits and examination of the material housed in their institutions.

Disclosure statement

No potential conflict of interest was reported by the author.

Author contributions

Ł. Czepiński designed, performed, analysed and drafted the research described in this article.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Foundation Universitatis Varsoviensis under Grant ‘Diversity of the horned dinosaurs from the Central Asia’; and University of Warsaw under Grants 17/II/2017 and 17/II/2018.