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Journal of Paleontology

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Journal of Paleontology 84(4):681-694. 2010
doi: http://dx.doi.org/10.1666/09-114.1

Mojoceratops perifania, A New Chasmosaurine Ceratopsid from the Late Campanian of Western Canada

Nicholas R. Longrich

Department of Geology, Yale University, New Haven, Connecticut 06520, USA nicholas.longrich@yale.edu

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.

Accepted: March 25, 2010

Keywords: Dinosauria, Ceratopsia, Chasmosaurinae, Dinosaur Park Formation

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Figure 1. Map showing the locations of sites that have produced fossils of Mojoceratops and cf. Mojoceratops. A, Red Deer River Valley (including Dinosaur Provincial Park), Alberta: AMNH 5656, AMNH 5401, NMC 1254; NMC 34832; TMP 1979.11.147; TMP 1983.25.1, TMP 1999.55.292, B, Lake Diefenbaker, Saskatchewan: NMC 8803.

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Figure 2. Stratigraphic chart showing the approximate stratigraphic position of Mojoceratops (NMC 8803) and cf. Mojoceratops (TMP 1979.11.147). The bonebed that produced NMC 8803 is correlated with the middle of the Dinosaur Park Formation. TMP 1979.11.147 comes from the base of the Dinosaur Park Formation (Centrosaurus faunal zone).

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Figure 3. Mojoceratops perifania TMP 1983.25.1, holotype. Autapomorphies of Mojoceratops include (1) a first epoccipital with accessory processes, (2) prominent swellings on the anterodorsal margin of the parietal caudal rami, and (3) shallow sulci on the anterior surface of the parietal lateral rami. Abbreviations: ejh, epijugal horn; fon, postorbital fontanelle; nar, naris; nas, nasal; par, parietal; phc, postorbital horn core, sq, squamosal; p1, p2, and p3 refer to parietal epoccipitals one, two, and three, respectively.

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Figure 4. Mojoceratops perifania TMP 1999.55.292, isolated lateral ramus of right parietal. Top, dorsal view; bottom, ventral view; p1, p2, and p3 refer to parietal epoccipitals one, two, and three, respectively; arrows point to the thickened and swollen anterodorsal margin of the parietal.

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Figure 5. Mojoceratops perifania NMC 8803, central bar and lateral rami of parietals. From top to bottom: dorsal view, proximal view, and ventral view. Arrows point to swellings on the thickened anterodorsal margin of the parietal.

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Figure 6. cf. Mojoceratops, AMNH 5656, subadult(?). Abbreviations: max, maxilla; par, parietal; qua, quadrate, sq, squamosal. p1, p2, and p3 refer to parietal epoccipitals one, two, and three, respectively.

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Figure 7. cf. Mojoceratops TMP 1979.11.147, skull roof. Abbreviations: fon, postfrontal fontanelle; nhc, nasal horn core; oc, occipital condyle; of, orbital fossa; ohc, orbital horncore.

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Figure 8. cf. Mojoceratops AMNH 5401, skull missing parietal. Areas of major reconstruction are shaded. Abbreviations: ep, epioccipital; epj, epijugal; ju, jugal; max, maxilla; phc, postorbital horncore; nas, nasal; nhc, nasal horncore; ros, rostral; sq, squamosal.

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Figure 9. Comparison of the skulls of Mojoceratops and other Campanian chasmosaurines. Not to scale.

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Figure 10. Strict consensus of 6 most parsimonious trees, showing the phylogenetic placement of the holotype of Mojoceratops perifania. A single unambiguous character (lateral rami of parietal posterior bar rod-like) supports a clade consisting of Mojoceratops and Agujaceratops. Consistency index excluding uninformative characters = .8041, retention index = .9003, rescaled consistency index = .7308.

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Online publication date: 1-Dec-2011.

Abstract & References : Full Text : PDF (710 KB) : Rights & Permissions

Margaret M. Yacobucci. (2011) Meta-analysis of character utility and phylogenetic information content in cladistic studies of ammonoids. Geobios
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Jordan C. Mallon, ^*, ¹ Robert Holmes, ² David A. Eberth, ³ Michael J. Ryan, ⁴ and Jason S. Anderson ⁵ . (2011) Variation in the Skull of Anchiceratops (Dinosauria, Ceratopsidae) from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta. Journal of Vertebrate Paleontology 31:5, 1047-1071
Online publication date: 1-Sep-2011.

Abstract & References : Full Text : PDF (1783 KB) : Rights & Permissions