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ABSTRACT-
A new genus of long-horned chasmosaurine ceratopsid is described from the Dinosaur Park Formation (upper Campanian) of Western Canada. Mojoceratops perifania is represented by a skull and a parietal from the Dinosaur Park Formation of Alberta and an isolated parietal from the Dinosaur Park Formation of Saskatchewan. Several other specimens are provisionally referred to this taxon. While Mojoceratops shares many plesiomorphies with Chasmosaurus, the animal lacks the forward-curving parietal epoccipitals and reduced postorbital horns that diagnose the genus Chasmosaurus, and it differs from all other chasmosaurines in exhibiting a prominent sulcus on the anterior margin of the parietal, swellings on the anterodorsal surface of the parietal rami, and a small accessory process on the first parietal epoccipital. Other unusual features include anteriorly extended parietal fenestrae, a broad, heart-shaped frill, and transverse expansion of the postfrontal fontanelle. The type material of "Eoceratops canadensis" and "Chasmosaurus kaiseni" are nondiagnostic and these names are therefore considered nomina dubia, but their morphology is consistent with Mojoceratops and they probably belong to this genus. The frill of Mojoceratops shows marked variation. Some of this variation probably results from intraspecific variation or ontogenetic changes, but because the Dinosaur Park Formation encompasses more than a million years of time, evolution may explain some of these differences. Phylogenetic analysis shows that Mojoceratops forms a clade with Agujaceratops mariscalensis; Chasmosaurus is the most basal member of Chasmosaurinae.
INTRODUCTION
DURING THE Late Cretaceous, the horned Ceratopsidae formed a major component of North America's fauna. Ceratopsids are particularly diverse in the late Campanian (Judithian) of Western Canada. The short-frilled Centrosaurinae dominate in terms of numbers, but the long-frilled Chasmosaurinae are a conspicuous part of this fauna as well (Currie and Russell, 2005). Currently, four taxa of chasmosaurine are recognized from the late Campanian of Canada. Three species are included in Chasmosaurus: Chasmosaurus belli (Lambe, 1902), Chasmosaurus russelli (Sternberg, 1940), and Chasmosaurus irvinensis (Holmes et al., 2001). A fourth taxon is represented by fragments of the parietosquamosal frill that were collected in the vicinity of Manyberries, southeast Alberta. These specimens, NMC 9813 and NMC 9814, have previously been referred to Anchiceratops (Ryan and Russell, 2001), but the morphology of the parietal in NMC 9814 most closely resembles Pentaceratops sternbergi (see Lehman, 1993), as the forward-curving...