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New material and systematic re-evaluation ofMedusaceratops lokii (Dinosauria, Ceratopsidae) from the Judith River Formation (Campanian, Montana)

Published online by Cambridge University Press: 28 November 2017

Kentaro Chiba
Affiliation:
Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, M5S 3B2, Canada 〈kentaro.chiba@mail.utoronto.ca〉
Michael J. Ryan
Affiliation:
Department of Vertebrate Paleontology, Cleveland Museum of Natural History, 1 Wade Oval Dr., University Circle, Cleveland, Ohio, 44106, USA 〈mryan@cmnh.org〉
Federico Fanti
Affiliation:
Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Alma Mater Studiorum, Università di Bologna, Via Zamboni, 67 - 40126 Bologna, Italy 〈federico.fanti@unibo.it〉Museo Geologico Giovanni Capellini, Via Zamboni, 63 - 40126 Bologna, Italy
Mark A. Loewen
Affiliation:
Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, 84112-0102, USANatural History Museum of Utah, Salt Lake City, Utah, 84108, USA 〈mloewen@umnh.utah.edu〉
David C. Evans
Affiliation:
Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, M5S 3B2, Canada 〈kentaro.chiba@mail.utoronto.ca〉Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario, M5S 2C6, Canada 〈d.evans@utoronto.ca〉

Abstract

Medusaceratops lokii Ryan, Russell, and Hartman,2010 is an enigmatic taxon of ceratopsid represented by partial parietals from the Mansfield bonebed in the Campanian Judith River Formation, Montana. Originally, all ceratopsid material collected from this bonebed was referred to the centrosaurine ceratopsidAlbertaceratops, but subsequently two parietals were designated the types of the chasmosaurine,M.lokii, in part, because they were interpreted to have three epiparietals bilaterally. Here we describe new material from the bonebed that allows a systematic revision of the taxon. A revised reconstruction of the frill, informed by newly discovered parietals, reveals thatM.lokii had a broad midline ramus and at least five epiparietals (ep) around the margin of the frill, both traits that are characteristic of Centrosaurinae. From medial to lateral, the epiparietal ornamentation consists of a small, variably procurving epiparietal (ep 1), an anterolaterally curving pachyostotic hook (ep 2), a smaller pachyostoic process (ep 3), and two small triangular epiparietals (ep 4 and 5). A phylogenetic analysis of ceratopsids, which is the first to includeMedusaceratops, indicates thatM.lokii is a unique, early centrosaurine ceratopsid taxon that is more closely related to Centrosaurini and Pachyrhinosaurini than Nasutoceratopsini. No unequivocal chasmosaurine bones or diagnostic material from any other ceratopsid could be identified from the Mansfield bonebed, suggesting that it represents one of the oldest occurrences of a monodominant accumulation of a centrosaurine ceratopsid on record.

Type
Articles
Copyright
Copyright © 2017, The Paleontological Society 

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