Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
PLoS One. 2011;6(8):e22710. doi: 10.1371/journal.pone.0022710. Epub 2011 Aug 10.
Centrosaurine ceratopsids are well known from the middle Campanian Upper Two Medicine Formation of Montana. Four taxa have been named: Brachyceratops montanensis, Rubeosaurus ovatus, Einiosaurus procurvicornis, and Achelousaurus horneri. Rubeosaurus has been historically the most enigmatic of these taxa; only two specimens, the holotype caudal parietal bar and a referred incomplete skull, have been assigned to Rubeosaurus.
METHODOLOGY/PRINCIPAL FINDINGS: A revised interpretation of the parietal processes of USNM 14765, the partial skeleton of a subadult centrosaurine formerly referred to Brachyceratops, indicates that it shares a P5 spike with the holotype of Rubeosaurus ovatus and should therefore be referred to that taxon. Brachyceratops is considered a nomen dubium.
CONCLUSIONS/SIGNIFICANCE: USNM 14765 provides additional anatomical information for Rubeosaurus ovatus. These new data are incorporated into a recent phylogenetic analysis of centrosaurine relationships; Rubeosaurus appears as the sister taxon of a clade composed of Einiosaurus, Achelousaurus, and Pachyrhinosaurus.
Centrosaurine 角龙类以蒙大拿州中坎潘阶上二叠统的中上二叠统而闻名。已经命名了四个分类单元：Brachyceratops montanensis、Rubeosaurus ovatus、Einiosaurus procurvicornis 和 Achelousaurus horneri。Rubeosaurus 一直是这些分类单元中最神秘的；仅有两个标本，模式标本尾方骨棒和一个未指定的不完整头骨，被分配给 Rubeosaurus。
方法/主要发现：对 USNM 14765 的顶骨突起的重新解释，该标本为亚成体 Centrosaurine 骨骼的一部分，以前被归入 Brachyceratops，表明它与 Rubeosaurus ovatus 的模式标本共享一个 P5 刺，因此应归入该分类单元。Brachyceratops 被认为是一个可疑名称。
结论/意义：USNM 14765 为 Rubeosaurus ovatus 提供了额外的解剖学信息。这些新数据被纳入最近的 Centrosaurine 关系的系统发育分析中；Rubeosaurus 出现在由 Einiosaurus、Achelousaurus 和 Pachyrhinosaurus 组成的进化枝的姐妹分类单元中。
