New Insights  on The Frill Ornamentations of Protoceratopsids

KENTARO CHIBA, MICHAEL J. RYAN, MOTOTAKA SANEYOSHI, SATOSHI KONISHI , YUDAI YAMAMOTO, DAVID C. EVANS, TSOGTBAATAR CHINZORIG, PUREVDORJ KHATANBAATAR, ZORIGT BADAMKHATAN, BUUVEI MAINBAYAR, KHISHIGJAV TSOGTBAATAR

Protoceratops andrewsi is a small-bodied, non-ceratopsoid ceratopsian dinosaur found in the Upper Cretaceous Djadokhta Formation in Mongolia. Although it has a well-developed parietosquamosal frill, the frill margin has been thought to be unadorned, unlike ceratopsids. On ceratopsids, especially centrosaurines, the subadult frill margin in dorsal view is typically undulated, with the apex of each undulation providing a locus onto which an epiparietal can potentially fuse and mature into a frequently modified shape that can aid in the identification of species. This study explicitly notes that the frill margin of P. andrewsi frill is undulated. Although virtually all P. andrewsi and a limited number of specimens of other protoceratopsids examined in this study have frill margin undulations, their development is variable and generally quite subtle; the size, number, and position of the processes are highly plastic among individuals and do not exhibit a consistent pattern related to the size of individuals. There is no sign that the undulations of P. andrewsi were associated with epiossifications. Due to the subtlety and inconsistency of the frill undulations, the potential functions of the frill margin undulations are currently not obvious. We also report several previously underappreciated protoceratopsid features that may have taxonomic utility within marginocephalians and important implications for understanding the evolution of the integumentary structures within Ceratopsia.

WINDOWS INTO SAUROPSID AND SYNAPSID EVOLUTION Essays in honor of Prof. Louis L. Jacobs

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