Xenoceratops foremostensis gen. et. sp. nov., a new centrosaurine ceratopsid from the Foremost Formation (Campanian) of Alberta, is described based on frill material from at least three adult-sized individuals collected from a low-density bone bed. The material can be assigned to Centrosaurinae based on features of the preserved squamosal. Although the parietals are incomplete, the shape of the diagnostic parietal can be inferred from several overlapping serial elements. The parietal of the new taxon shares with all other centrosaurines, except Centrosaurus apertus, spike-like ornamentation at the posterolateral (P3) locus under traditional coding methods. At approximately 78 Ma, it is the oldest known Canadian ceratopsid, approximately 0.5 Ma older than Albertaceratops from the lower Oldman Formation of Canada and approximately 1.0 Ma younger than Diabloceratops from the Wahweap Formation of Utah. A phylogenetic analysis resolves the new taxon as the basalmost centrosaurine and places Centrosaurus brinkmani as the sister taxon to Styracosaurus albertensis. The type species of Centrosaurus brinkmani is moved to a new genus.
Ceratopsidae is the most speciose clade of dinosaurs known from the Late Cretaceous of Laramidia. The fossil-rich Belly River and Edmonton groups of Alberta, Canada, alone have produced at least 13 ceratopsid species, including the centrosaurines Albertaceratops nesmoi Ryan, 2007, Centrosaurus apertus Lambe, 1904, Centrosaurus brinkmani Ryan and Russell, 2005, Pachyrhinosaurus canadensis Sternberg, 1950, Pachyrhinosaurus lakustai Currie et al., 2008, Spinops sternbergorum Farke et al., 2011, and Styracosaurus albertensis Lambe, 1913, and the chasmosaurines Anchiceratops ornatus Brown, 1914, Arrhinoceratops brachyops Parks, 1925, Chasmosaurus belli Lambe, 1902, Chasmosaurus russelli Sternberg, 1940, Vagaceratops irvinensis Holmes et al., 2001, and Triceratops horridus Marsh, 1889, with five of these having been named within the last two decades. Most of these taxa have been recovered from the well-sampled sediments of the upper Belly River Group, particularly the Dinosaur Park Formation, from the region of Dinosaur Provincial Park (DPP). The Dinosaur Park Formation was deposited during a transgressive phase of the Western Interior Seaway. The older regressive phase of this clastic wedge, recorded in the rocks of the Oldman and Foremost formations, has received comparatively little attention, due in part to the perceived scarcity of dinosaur remains from these units.
The Foremost Formation is the most poorly known unit in terms of its dinosaur fauna. It comprises mostly marine sediments deposited during the transgression of the Claggett cycle, but is transitional between the underlying fully marine shales of the Pakowki Formation and the overlying fully non-marine Oldman Formation (Eberth and Hamblin 1993). The formation is bounded below by the Mackay Coal and above by the Taber Coal zones (Fig. 1), and can be up to 83 m thick (including subsurface), but is typically limited to 10–30 m in outcrop. The upper portion of the formation contains a localized near-shore terrestrial sequence that is capped by the Harrington sandstone, which has been argued to be the lowermost portion of the Oldman Formation (Eberth and Hamblin 1993). Microvertebrate sampling has revealed a dinosaur assemblage that resembles other later units in terms of family-level representation (Baszio 1997; Ryan and Russell 2001; Brinkman et al. 2004; Frampton 2007). The only ornithischian taxon described on the basis of non-dental skeletal elements is the pachycephalosaurid Colepiocephale lambei (Schott et al. 2011). Several partial hadrosaurine skeletons have also been collected, and one of these has been referred to as “Kritosaurus” (Brett-Surman 1989), but these have not yet been formally described or placed into phylogenetic context.
The best exposures of the lower Belly River group, including the Foremost Formation, occur along the Milk, Oldman, and South Saskatchewan rivers (Fig. 2), as well as in Chin Coulee in the extreme southern part of Alberta. The region has previously been explored by crews from the National Museum of Canada (now the Canadian Museum of Nature) and the Royal Ontario Museum (ROM) in the middle of the 20th century, and more recently by crews from the Royal Tyrrell Museum (TMP), ROM, and the Cleveland Museum of Natural History. Recent examination of material collected by Wann Langston, Jr., in 1958 has revealed previously undescribed, well-preserved ceratopsid cranial material from the Foremost Formation of Alberta. Here we describe this material and refer it to a new taxon, Xenoceratops foremostensis gen. et. sp. nov., which represents the oldest ceratopsid taxon known from Canada.
Canadian Museum of Nature (CMN), Ottawa, Ontario, Canada; Royal Ontario Museum (ROM), Toronto, Ontario, Canada; Royal Tyrrell Museum of Palaeontology (TMP), Drumheller, Alberta, Canada.
Order Ornithischia Seeley, 1888
Suborder Ceratopsia Marsh, 1890
Neoceratopsia Sereno, 1986
Family Ceratopsidae Marsh, 1888
Subfamily Chasmosaurinae Lambe, 1915
Xenoceratops gen. nov.
Xenos (from the Greek), meaning foreign or alien, and ceratops (from the Greek), meaning horned face, referring to the lack of ceratopsian material known from the Foremost Formation.
Centrosaurine ceratopsid with two epiparietals (P2–P3) on the posterior parietal ramus; wide-based, short, thick, procurved processes (P2) adjacent to the midline bar and an elongate, dorsoventrally depressed spike (P3) at the posterolateral margin oriented posterolaterally; additional epiparietals fuse into ovoid depressions on the lateral ramus; ventral margins of parietal at the contact with the epiparietals greatly inflated.
The P1 epiparietal is missing as on the basalmost centrosaurines (Albertaceratops and Diabloceratops) as well as the derived “pachyrhinosaur”-grade (sensu Currie et al. 2008) centrosaurs Achelousaurus, Einiosaurus, and Pachyrhinosaurus. The P2 epiparietal is a thickened protrusion compared to the elongate, medially curled, finger-like process of Centrosaurus apertus and Pachyrhinosaurus or the short tab-like processes on Achelousaurus, Einiosaurus, and some specimens of Styracosaurus. Unlike other centrosaurines, Xenoceratops lacks the development of imbricated epiparietals on the lateral ramus and shares with Albertaceratops and most Chasmosaurinae the lack of “bumps” on the midline parietal ramus.
Xenoceratops foremostensis sp. nov.
As for the genus.
Named for the Village of Foremost, Alberta.
CMN 53282. A partial parietal (Fig. 3).
CMN 54952 to CMN 54965.
The material originally catalogued as CMN 53282 is a composite of at least three adult-sized individuals. CMN 53282 is retained for the holotype, with CMN 54950 and CMN 54951 designated as paratype parietals representing two other individuals. The remainder of the referred material is assigned sequential specimen numbers CMN 54952 to CMN 54964 (CMN 54952, parietal (Figs. 6F, 6G); CMN 54953, parietal (Figs. 6D, 6E); CMN 54954, squamosal (Figs. 8A–8C); CMN 54955, nasal (Fig. 8D); CMN 54956, squamosal (Fig. 8E); CMN 54957, squamosal; CMN 54958, parietal (Fig. 6H); CMN 54959, parietal P4 process; CMN 54960, parietal with P3 suture; CMN 54961, epiparietal (Fig. 6C); CMN 54962, epiparietal (Fig. 6B); CMN 54963, epiparietal (Fig. 6A); CMN 54964, parietal); none of this material can be confidently referred to the holotypes or paratypes, but likely pertain to these type specimens owing to their close association. CMN 54965 is assigned to all remaining unidentified fragments originally part of the CMN 53282 designation.
The type and referred specimens were collected by Wann Langston, Jr., in 1958, from moderately developed Foremost Formation badlands of Chin Coulee, located approximately 7 km northeast of the Village of Foremost (Fig. 2). All the material was collected from a low-diversity bone bed in a “soft gray-brown slightly carbonaceous shale that is 17 feet above the massive yellow-weathering Ostrea bed” (Chin Coulee Site No. 2; W. Langston, Jr., unpublished 1958 field notes on file at the Canadian Museum of Nature) in Chin Coulee (Fig. 2). More precise locality is on file with the Canadian Museum of Nature, Ottawa, Ontario, Canada.
The holotype parietal (CMN 53282, Figs. 3A–3F) is the most complete element composed of three fragments; 1, most of the posterior midline ramus, a portion of the left posterior and lateral ramus preserving the P2 and P3 (and probably P4) processes, and adjacent margins of the parietal fenestra; 2, the anteriormost right parietal ramus fragment with a fused epiparietal (Figs. 3E and 3F); and 3, the isolated right P2 process (Fig. 3A). All these fragments were collected in two small field jackets, and parts of each piece were preserved in direct contact with one another; this fact, plus their similar size, color, and texture suggests that elements pertain to the same individual. The paratypes, CMN 54950 (Fig. 4) and CMN 54951 (Fig. 5), are portions of right posterior parietal rami, which, owing to differences in their size and overlapping anatomy, must be from different individuals.
As reconstructed, when viewed dorsally, the parietal has fenestrae of typical centrosaurine size adjacent to a wide midline ramus (Fig. 7A). The parietal P1 process is not expressed in this taxon, but it does possess P2 and P3 processes and a minimum of two (probably five, as per other centrosaurines based on inference from the available fragments) additional processes are present along the margin of the lateral parietal ramus. The wide-based, short, and pachystotic P2 processes (Figs. 3A–3D, 4A–4D) lie medial to a U-shaped posterior margin and are curled slightly dorsolaterally. The P3 process is a depressed, wide-based, elongate, straight spike that is posterolaterally oriented (Figs. 3B–3D, 5A, 5B).
Xenoceratops appears to have lacked scalloped lateral rami. The margins of the lateral parietal rami have ovoid depressions (Figs. 6D–6G) that appear to correspond to the loci along the scalloped margins of other centrosaurs where the epiparietals fuse. The partial right anterior lateral ramus of the holotype (Figs. 3E, 3F) preserves the butt suture contact surface for the squamosal that is of typical centrosaurine shape. This surface forms an approximately right angle with the lateral margin of the ramus. The element has a fused sub-triangular epiparietal at the anterolateral corner that would have partially straddled the contact with the squamosal.
The specimens include hundreds of unidentifiable small fragments. Identifiable pieces are typically larger than 20 mm. Only diagnostic frill specimens and informative fragments will be discussed here. Numbering of the epiparietals follows Sampson et al. 1997, but see the phylogenetic analysis section for comments about the new coding methodology of Farke et al. (2011).
CMN 54955 (Fig. 8D) is a fragmentary right nasal preserving the base of the ornamentation and a portion of the lateral wall. The specimen is very similar to isolated, unfused Medusaceratops nasals recovered from the Mansfield bone bed in the Judith River Formation of Montana (Ryan 2007, fig. 5). These unfused nasals are mediolaterally flattened with low, elongate ornamentation that is also seen on the basal centrosaurines Albertaceratops (Ryan et al. 2010) and Diabloceratops (Kirkland and Deblieux 2010); CMN 54955 probably had a similar nasal ornamentation. Basal length of the ornamentation cannot be estimated owing to the incompleteness of the specimen, and the surficial texture is poorly preserved.
Midline ramus: Two partial midline rami, CMN 53282 and CMN 54958, were recovered, with the former (holotype) being the most complete. It is mediolaterally wide and arched in cross-section as in Albertaceratops and differs from the strap-like or square-shaped rami of chasmosaurs or the depressed, triangular cross-sectional-shaped rami of most other centrosaurs.
The posterior margin has a shallow U-shaped median embayment when viewed dorsally, which is constrained by the medially positioned P2 processes. The posterior margin of the bar is thickest (54 mm) approximately 15 mm from the posterior margin and then tapers to form a horizontal ridge. Similar to Albertaceratops and Chasmosaurinae, but differing from other centrosaurines, Xenoceratops lacks any “bumps” on the midline ramus when viewed laterally. Portions of the posterior margin of the left parietal fenestra are preserved on CMN 53282 (Figs. 3C, 3D). The bone immediately adjacent to the fenestra is thin (<2 mm) with the parietal becoming thicker towards the posterior and lateral margins. As reconstructed (Fig. 7A), the fenestrae were ovoid openings of typical centrosaurine size.
Posterior and lateral rami and ornamentation: Four significant pieces of parietal rami can be identified, including CMN 53282, the most complete parietal (in two sections) preserving left processes P2–P4 and portions of the fenestra (Figs. 3A–3F), and a portion of the left anterior ramus with the contact for the squamosal and a large fused epiparietal (Figs. 3E, 3F); CMN 55950 (Figs. 4A–4D), a partial right parietal preserving the P2 process, a large open suture for the P3 process, and a portion of the divot-like depression for the P4 epiparietal; and CMN 54951 (Figs. 5A, 5B), a right P3 spike with a portion of the P2 preserved. Other fragmentary parietal pieces include a partial posterior portion of a parietal midline ramus (CMN 54958, Fig. 6H), at least three partial epiossifications (CMN 54963, Fig. 6A; CMN 54962, Fig. 6B; CMN 54961, Fig. 6C), and fragments of the lateral parietal margin preserving ovoid divots (CMN 54953, Figs. 6D, 6E; CMN 54952, Figs. 6F, 6G; and CMN 54964).
P2: The left P2 process of CMN 53282 (Figs. 3B–3D) and the right P2 process of CMN 54950 (Figs. 4A–4D) are indistinguishably fused to the underlying parietal and have pronounced texturing on the superior surface (the right P2 process of CMN 53282 (Fig. 3A) is an isolated fragment). This texture starts just above a slight inflation that occurs at the base of the process close to the ventral parietal surface and extends across the process to the apex. The P2 processes of CMN 53282 are smaller and more symmetrical than that of CMN 54950, which is more robust and has a more pronounced dorsolateral inflection. The dimensions of the P2 processes are as follows: CMN 53282 (left P2): 117 mm basal length, 40 mm basal thickness, and 41 mm height; CMN 54950: estimated length and thickness of 138 mm and 42 mm, respectively. The isolated right P2 fragment from CMN 53282 is similar in size and shape to its left counterpart.
P3: On CMN 53282 (Figs. 3B–3D), this process is a broad-based, depressed spike with a slight ventral inflection. It is triangular in cross-section with a distinct raised margin on the dorsal surface running perpendicular to the long axis. Both the lateral and medial surfaces have sharp margins. When viewed dorsally the lateral margin is straight and the medial margin gently curves towards the blunt apex. The maximum preserved length of P3 is 200 mm (approximately 20 mm is missing from the apex), basal width is 160 mm and basal thickness is 42 mm.
CMN 54951 (Fig. 5) is an isolated right P3 spike missing the apex that preserves a small portion of the parietal ramus and the lateral side of the P2 epiparietal. It differs from that of CMN 53282 by having a narrower base (preserved length approximately 210 mm; basal thickness 38 mm). It also has a triangular cross-section, but in this case the cross-sectional shape is defined by a flattened lateral surface.
CMN 54950 is notable for having a massive ovoid (approximately120 mm × 56 mm) sutural surface (Fig. 4D) for a P3 process. This surface is deeply textured with wide (approximately 10 mm) pits. Although the dorsal margin of the suture is level with the surface of the adjacent ramus, the ventral margin is inflated, as is also seen on several parietal fragments that preserve the divot-like depressions for the epiparietals (CMN 54953, Figs. 6D, 6E; CMN 54952, Figs. 6F, 6G; and CMN 54964). CMN 54960 is a fragmentary left parietal that also has a P3 sutural surface; however, it is significantly smaller (approximately 83 mm × 23 mm, as preserved) than that of CMN 54950 and probably came from a smaller individual.
P4: Adjacent to the P3 on CMN 53282 (Figs. 3C, 3D) is an elongate, raised, ovoid surface that most likely represents a highly fused P4 epiparietal. CMN 54959 is an isolated parietal fragment that appears to preserve the same portion of the ramus from the right side. It has a ventrally inflated, ovoid lateral surface 55 mm in length with a moderately raised midline keel that probably also represents a well-fused P4 process. A partial P4 suture is preserved on CMN 54950 (Fig. 4D).
Additional parietal epiossifications: As in other centrosaurines, Xenoceratops has additional epiossifications along the lateral rami between P3 and the contact joint between the parietal and squamosal. The preserved epiossifications (CMN 54963, Fig. 6A; CMN 54962, Fig. 6B; CMN 54961, Fig. 6C) and the epiparietal on CMN 53282 are robust, triangular-shaped, and more typical of chasmosaurine epiossifications, although they are similar to some of those seen on the basal centrosaurine, Diabloceratops, from the Wahweap Formation of Utah. Unusually for any ceratopsids, these epiossifications appear to fuse into the previously described small, ovoid depressions on the margin of the lateral rami. These are probably homologous to the epiparietal fusion loci of the parietal margins of other centrosaurines. Several isolated fragments from the bone bed preserve these depressions (e.g., CMN 54592 (Figs. 6F, 6G) and CMN 54593 (Figs. 6D, 6E), 73 and 50 mm in length, respectively, the latter estimated), and a portion of a very large one can be seen on CMN 54950 lateral to the open P3 suture. Notably, the ventral margins of these depressions arch below the adjacent ventral surface of the parietal.
Parietal–squamosal contact: CMN 53282 (Figs. 3E, 3F) preserves the anterior portion of the right parietal ramus including the open butt suture for the squamosal. This is broken near its lateral margin, but the preserved medial portion exhibits the typical fluted texture seen on most centrosaurs. Laterally adjacent to the suture is a large, sub-triangular epiparietal (basal width 88 mm, height 84 mm, basal thickness 33 mm). As interpreted here, this epiparietal is fused as in other centrosaurines to an outgrowth of the parietal over which it is draped. The base is well-fused along the medial margin but becomes more distinct laterally where it can be distinguished as an overgrowth of the underlying bone. Several small foramina penetrate the ventral margin and puncture the dorsal surface near the medial margin. The epiparietal has a slight dorsal inclination that is enhanced by its flat dorsal surface and inflated ventral surface. Posteriorly adjacent to the epiparietal the margin of the ramus has an ovoid thickening that is interpreted as a well-fused epiparietal. Although this epiparietal is highly modified, it retains a rugose, ventrally inflated surface typical of highly fused epiossifications (e.g., CMN 53282).
Numerous squamosal fragments were recovered. The largest, CMN 54594, is a left squamosal (Figs. 8A–8C) that preserves portions of the medial and posterolateral margins, contact surfaces for the exoccipital and quadrate, and the anterior blade. CMN 54594 preserves the diagnostic groove between the “stepped” anterior and posterior portions of the element that wraps around from the ventral and dorsal surfaces. In ceratopsids this groove is only known in centrosaurines (Ryan 2007), although it has also been noted on the non-ceratopsid neoceratopsian Protoceratops (A. Farke, personal communication, 2012). The muscle scar on the ventral surface behind the posterodorsal margin of the quadrate contact groove is larger and more robust than the same feature on any centrosaurine from the younger Oldman and Dinosaur Park formations. CMN 54957 is a portion of a squamosal preserving the broken muscle scar from a squamosal similar in size to CMN 54954. CMN 54956 (Fig. 8E) is a fragment of the posterolateral margin of a left squamosal of typical centrosaurine shape (e.g., ROM 1927).
To access the systematic position of Xenoceratops foremostensis, the holotype specimen was coded into the data matrix of Farke et al. (2011), using both “traditional” and “new” (sensu Farke et al. 2011) coding. The traditional numbering methodology applied to all centrosaurs (Sampson et al. 1997) is based on the adult ornamentation of Centrosaurus apertus, where the ornamentation locus immediately adjacent to the midline on the dorsal surface (large procurving hook) is designated as P1. In this system, the P1 process is absent on Achelousaurus, Einiosaurus, and Pachyrhinosaurus, and P1 and P2 are absent on both Albertaceratops and Diabloceratops. The recently proposed alternate codings of Farke et al. (2011) use a different interpretation for numbering parietal ornamentation, where P1 still assumes the Centrosaurus apertus-like loci on the dorsal surface of the parietal adjacent to the midline, but the first process on the posterior margin adjacent to the midline is designated P2, whether it is a medially curving hook, as on Centrosaurus apertus and Pachyrhinosaurus, or a spike, as on Spinops.
The data matrix consists of 97 characters scored for 16 ingroup taxa and three outgroup taxa using the revised methodology of Farke et al. (2011) (Table 1). The taxa were also coded using the traditional method of Sampson et al. (1997), and these are listed as characters 98–108 in Table 1. Note that character 50 (parietal, sharp median crest) has been reinterpreted and recoded for the absence (0) or presence (1) of parietal midline “bumps” visible in the lateral view. The following characters were also recoded based on new observations of original holotype or referred specimens, or alternative interpretations of published characters: Zuniceratops christopheri, 20(?→0), 49(0→?); Diabloceratops eatoni, 52(1→0); Albertaceratops nesmoi, 49(1→0); Centrosaurus apertus, 30(0→2); Centrosaurus brinkmani, 61(?→1), 62(?→1), 66(?→1), 67(?→0), 68(?→1); Styracosaurus albertensis, 60(2→(02)); Spinops sternbergorum, 60(0→3); Pachyrhinosaurus canadensis, 53(?→1), 57(?→1), 58(?→0), 59(?→1), 60(?→2), 61(?→1), 62(?→1), 63(?→0), 64(?→1), 65(?→0), 66(?→1), 67(?→0), 68(?→1), 74(?→1), 80(?→0), 95(?→1); Pachyrhinosaurus lakustai, 60(2→(02)); Chasmosaurus belli, 10(?→1), 49(1→0); Pentaceratops sternbergii, 49(1→0); Sinoceratops zhuchengensis, 50(?→1). Although McDonald (2011) presented revised codings for Rubeosaurus, the taxon is problematic and we have chosen to use characters from the original diagnosis pending a reevaluation of the taxon.
A cladistic analysis was performed using both the new and the traditional codings under the branch-and-bound parsimony algorithm in PAUP* 4.0b10 (Swofford 2003) with all 97 characters equally weighted and run unordered. Using the new codings resulted in three most parsimonious trees. The strict consensus tree (tree length = 137 steps, CI = 0.74, and RI = 0.76) differs only in terms of the topology of the outgroup taxa (Protoceratops, Turanoceratops and Zuniceratops) and is shown in Fig. 9, along with bootstrap values (1000 replicates) to describe the relative robustness of the topology. Note that coding characters 58–68 of Xenoceratops as per Farke et al. (2011) (i.e., the parietal process nearest the midline = P1, spike = P2, etc.) or using the traditional methodology of Sampson et al. (1997) produced identical results when all other taxa were coded and analyzed as per Farke et al. (2011).
Analysis of all taxa using traditional codings (characters 98–108 substituting for characters 58–68) produced 2814 trees. A strict consensus tree (length = 136 steps; CI = 0.73; RI = 0.73) provided little resolution for the relationships of Xenoceratops above the level of Centrosaurinae.
A phylogenetic analysis of Xenoceratops using the assumptions of Farke et al. (2011) resulted in three most parsimonious trees of 137 steps each, differing only in the positions of the three outgroup taxa, and recovered Xenoceratops as the sister taxon to all other centrosaurines. This analysis has significantly better resolution than that presented by Farke et al. (2011) probably due in part to the additional scoring of missing characters for taxa such as Centrosaurus brinkmani and Pachyrhinosaurus canadensis from direct observation of original material.
Using the traditional characters of Sampson et al. (1997), Xenoceratops could not be resolved within Centrosaurinae. However, coding the parietal processes of Xenoceratops using either methodology and running the analysis using the assumptions of Farke et al. (2011) produced the same results with the same CI and RCI values. Notably, the phylogenetic analysis no longer results in a sister taxon relationship between Centrosaurus brinkmani and Centrosaurus apertus. Centrosaurus brinkmani is therefore referred to a new genus, Coronosaurus brinkmani (comb. nov.). A revised diagnosis is provided in Appendix A.
Xenoceratops foremostensis is the first described ceratopsian from the Foremost Formation of Alberta and represents the oldest known ceratopsid from Canada. The material comes from a small quarry that includes diagnostic parietal ornamentation from at least three individuals and can be interpreted as a bone bed (sensu Eberth et al. 2007). The morphology of the parietal–squamosal contact and the presence on the squamosal of a narrow groove that runs across the medial surface at the angle of the “stepped up” margin identifies the material as centrosaurine (Ryan 2007). Although a complete parietal is not present, the available parietal specimens can only be reasonably assembled into one morphology (Fig. 7A).
As reconstructed, the parietal of CMN 53282 has a thickened U-shaped midline posterior margin similar to that seen in centrosaurines that support large P3 spikes (e.g., Albertaceratops (Fig. 7E) and Diabloceratops (Fig. 7H)). Similar to all centrosaurines except Centrosaurus apertus, Xenoceratops has large spikes at the P3 loci (although notably the large Centrosaurus apertus skull, CMN 348, has a large right P3 process that is very spike-like). These differ from all other centrosaurines except Albertaceratops (Fig. 7E) and the chasmosaurine Medusaceratops lokii (Ryan et al. 2010) from Montana in being wide-based and pachystotic, and differs from those two ceratopsids in that the processes are straight not curled. Xenoceratops lacks P1 processes, as do Achelousaurus (Fig. 7D), Albertaceratops, Einiosaurus (Fig. 7G), and Pachyrhinosaurus (Fig. 7F); the only other centrosaurines with large P3 spikes, Rubeosaurus and Styracosaurus (Fig. 7C), lack or have reduced P2 processes, respectively.
The P2 processes are wide-based and pachystotic and would have been positioned medial to the posterior midline. In overall morphology it resembles the P4 processes of Albertaceratops, but the P2 of Xenoceratops has a pronounced dorsal inflection. The P2 process of CMN 54950 is more robust than that of CMNH 53282 and has an almost hook-like shape when viewed in lateral profile.
Xenoceratops is apomorphic in having ovoid depressions with arched ventral margins occurring at the positions on the lateral parietal margin where epiparietals contact and fuse on other centrosaurines. This interpretation is confirmed by the presence of a partially preserved depression on CMN 54950 at the P4 loci and the presence of a highly fused epiparietal on CMN 53282 at the same position. As interpreted here, the epiparietals fuse into the parietal marginal depressions and then undergo the typical sequence of fusion to the underlying bone. The epiparietal that partially straddles the contact between the parietal and squamosal appears to have the typical centrosaurine contact of overlapping an outgrowth of the parietal.
The anteriormost preserved midline ramus of Xenoceratops has an arched cross-section rather than the triangular cross-section that is seen at this position on most centrosaurines. Albertaceratops appears to have a similar cross-sectional shape, but this is difficult to confirm owing to the preservation of the only known specimen.
Although no identifiable portions of the postorbitals were preserved with the specimens, an additional, unprepared fragmentary skull (TMP 2010.76.24) was collected from the Foremost Formation in the same region in 2010 that does preserve portions of two large-diameter, elongate postorbital horncores. This material can be referred to Xenoceratops based on the presence of apomorphic, shallow epiparietal contacts on parietal fragments that were recovered with the specimen. From this, we infer that Xenoceratops had elongate, robust postorbital horncores similar to the similarly aged basal centrosaurines Albertaceratops and Diabloceratops.
Although fragmentary, the preserved nasal fragment suggests that Xenoceratops may have had an elongate, low nasal ornamentation similar to that of Medusaceratops and that which has been reconstructed for Albertaceratops (Ryan 2007).
The recognition of Xenoceratops foremostensis is a significant addition to the dinosaurian faunal record for the lower portion of the Belly River Group. With the exception of the pachycephalosaur, Colepiocephale lambei (Schott et al. 2011), all other dinosaur taxa from the Foremost Formation have been erected based on teeth collected primarily from microvertebrate fossil localities. The relative lack of diagnosable skeletal material is related to the limited amount of exposures in the near-shore terrestrial sequence that constitutes the top of the formation. However, the data from these dinosaurs and the microvertebrate localities indicate that the dinosaurs in the formation are similar at the family level to those in both the overlying Oldman and Dinosaur Park formations (Baszio 1997; Brinkman et al. 2004; Frampton 2007), albeit representing more basal members of these clades. Future work on the tempo and mode of dinosaurian evolution in the Belly River Group will require the recovery and description of more taxa from the regressive lower half of the Belly River Group (Oldman and Foremost formations), where the dinosaur faunas remain poorly known.
The mansucript was improved by comments from Rob Holmes and an anonymous reviewer. Wann Langston, Jr., discovered the specimens and generously answered inquires about the material. Margaret Currie (CMN) assisted in relocating unprepared material from Langston’s quarry. Ian Morrison and volunteers at the ROM puzzled over the fragments and helped to reassemble the specimens. Danielle Dufault drew line illustrations in Figs. 3 and 8. Thanks to all the students and volunteers of the 2009 Southern Alberta Dinosaur Project (SADP) who assisted in relocating the original quarry. This work was supported, in part, by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to David Evans.
- Received May 26, 2012.
- Accepted July 16, 2012.
- Published on the NRC Research Press Web site at http://cjes.nrc.ca on November 8, 2012.
- Published by NRC Research Press
Order Ornithischia Seeley, 1888
Suborder Ceratopsia Marsh, 1890
Neoceratopsia Sereno, 1986
Family Ceratopsidae Marsh, 1888
Subfamily Centrosaurinae Lambe, 1915
Genus Coronosaurus gen. nov. previously Centrosaurus brinkmani (Ryan and Russell 2005)
Coronosaurus refers to corona (Latin), for crown, and saurus (Latinized Greek), meaning “lizard”, in reference to the multiple occurrences of extra epiparietals that cover the posterior margin of the parietal, giving it a crown-like appearance.
Coronosaurus brinkmani (Ryan and Russell 2005).
Unless otherwise noted in Ryan and Russell (2005), all the ceratopsid material from BB 138 in Dinosaur Provincial Park, Alberta, and the Milk River Ridge bone bed (MRR BB) near Warner, Alberta, is referred to Coronosaurus brinkmani. Material is listed in Ryan (2003), a copy of which is on file with the Royal Tyrrell Museum of Palaeontology. Significant representatives of the parietal, postorbital, and supraorbitals include TMP 2002.68.3 (Ryan and Russell 2005, fig. 3a), TMP 2002.68.10 (Ryan and Russell 2005, figs. 3d, 3e), and TMP 2002.68.5 (Ryan and Russell 2005, fig. 3f), respectively.
Bone bed 138, Dinosaur Provincial Park, approximately 50 km from Brooks, Alberta, Canada (12 463090E, 5621680N (WGS 84)), Oldman Formation, 14.6 m below the contact with the Dinosaur Park Formation (645 m above sea level), referable to the Comrey sandstone (Eberth 2005). Additional referred specimens from the MRR BB near Warner, Alberta, approximately 180 km southwest of BB 138, are also from the Oldman Formation. Exact locality information of this bone bed is on file with the TMP.
As for the type and referred localities.
Adult-sized supraorbital horn cores are inflated (but not elongated as in Zuniceratops, chasmosaurines, Albertaceratops, and Diabloceratops) and project laterally over the orbit; sub-adult-sized postorbital horn cores have an attenuated pyramidal shape with a slight lateral inflection of the distal one half; posterior parietal bar has a number of accessory epiparietal ossifications that fuse to the posterior and dorsal surfaces and through ontogeny develop as short spines that may fuse along their adjacent margins into larger, irregular masses. They contribute to the substance of P1 and, through fusion, form the composite epiparietal at the P2 loci. The P3 epiparietal is variably developed as a short tongue-like hook or tapered spike that is dorsolaterally oriented.