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(Some) Brachyceratops are really Rubeosaurus
This just in:
McDonald AT, 2011 A Subadult Specimen of Rubeosaurus ovatus (Dinosauria:
Ceratopsidae), with Observations on Other Ceratopsids from the Two
Medicine Formation. PLoS ONE 6(8): e22710.
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.
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.
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
While the holotype material of Brachyceratops montanensis and other
specimens from the original quarry remain undiagnostic centrosaurine in
MacDonald's opinion. However, referred specimens of Brachyceratops
(including the excellent Smithsonian specimen USNM 14765 and MOR 492 show
derived traits of R. ovatus.
On a side note, the phylogenetic analysis places Sinoceratops deep inside
Centrosaurinae, as the sister to the Rubeosaurus + (Einiosaurus +
Thomas R. Holtz, Jr.
Email: firstname.lastname@example.org Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Faculty Director, Science & Global Change Program, College Park Scholars
Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA