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A new species of Chasmosaurus (Dinosauria: Ceratopsia) from the Dinosaur Park Formation of southern Alberta

Robert B. Holmes, Catherine Forster, Michael Ryan, and Kieran M. Shepherd 0

Abstract: Chasmosaurus irvinensis (sp. nov.) is distinguished from other species of this genus by the possession of a broad snout, absence of a brow horn (the position of which is occupied by a pit or rugosities suggestive of bone resorption), broadly rounded and open jugal notch, subrectangular squamosal, straight posterior parietal bar bearing 10 epoccipitals, eight of which are flattened, strongly curved anterodorsally, and nearly indistinguishably coossified to their neighbours, and small, transversely oriented parietal fenestrae restricted to the posterior portion of the frill. This species, restricted to the upper part of the Dinosaur Park Formation, is significantly younger than the other recognized Canadian Chasmosaurus species, C. belli and C. russelli. Phylogenetic analysis shows that C. irvinensis is most closely related to the other Canadian Chasmosaurus species and more distantly related to Chasmosaurus mariscalensis from Texas. Résumé : Chasmosaurus irvinensis (sp. nov.) se distingue des autres espèces de ce genre par son large boutoir, l’absence d’une corne sur le front (cette position est occupée par une fossette ou des rugosités qui suggèrent une résorption osseuse), une encoche jugale généralement arrondie et ouverte, un temporal presque rectangulaire, une barre pariétale postérieure droite comportant 10 époccipitaux, dont huit sont aplatis et fortement recourbés, dirigées en position antéro-dorsale et co-ossifiés à leurs voisins de façon presque indistincte, ainsi que de petites fenêtres pariétales à orientation transversale restreintes à la partie arrière de la collerette. Cette espèce, limitée à la portion supérieure de la Formation de Dinosaur Park, est beaucoup plus jeune que les autres espèces canadiennes de Chasmosaurus, C. belli et C. russelli. Une analyse phylogénique montre que C. irvinensis est plus étroitement lié aux autres espèces canadiennes de Chasmosaurus et moins étroitement lié au Chasmosaurus mariscalensis du Texas. [Traduit par la Rédaction]

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The Ceratopsidae comprises 13 named genera (excluding the problematic Brachyceratops and Monoclonius) distributed between the subfamilies Centrosaurinae and Chasmosaurinae. The centrosaurines have figured prominently throughout the history of North American dinosaur work, from the description of the first horned dinosaur Monoclonius (Cope 1876; = Centrosaurus) to the most recently described genera Einiosaurus and Achelousaurus (Sampson 1995). In marked contrast, all seven chasmosaurine genera were named between 1889 (Triceratops Received December 4, 2000. Accepted April 5, 2001. Published on the NRC Research Press Web site at http://cjes.nrc.ca on October 19, 2001. Paper handled by Associate Editor H.-D. Sues. 100

R. Holmes.1 Research Division, Palaeobiology, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, ON K1P 6P4, Canada. C.A. Forster. Department of Anatomical Sciences, State University of New York, Stony Brook, NY 11794, U.S.A. M. Ryan. Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, AB T0J 0Y0, Canada. K. Shepherd. Collections, Canadian Museum of Nature. P.O. Box 3443, Station D, Ottawa, ON K1P 6P4, Canada. 1

Corresponding author (e-mail: rholmes@mus-nature.ca).

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Marsh) and 1925 (Arrhinoceratops Parks), and only two currently recognized species, Chasmosaurus russelli (Sternberg 1940) and C. mariscalensis (Lehman 1989) have been named since that time. In this paper, a new species of chasmosaurine ceratopsid, Chasmosaurus irvinensis, is described. The type specimen (NMC 41357) was discovered by Mr. Luke Lindoe near Irvine, Alberta, and collected under the direction of Dr. Wann Langston in 1958. It comprises most of the skull and postcranial skeleton preserved in an upright, crouched posture. Except for the snout, which had fallen to pieces before discovery and was collected as surface float, the skeleton was removed in one large block and shipped to the National Museum of Natural Sciences (now the Canadian Museum of Nature) in Ottawa. Based on the shape of the partially exposed frill, it was identified tentatively in the field as Chasmosaurus belli. Presumably since this taxon was relatively well known, the specimen was stored, and the jackets remained unopened. Preparation was initiated in the late 1980s by Drs. Wann Langston and Dale Russell to address the ongoing debate surrounding forelimb posture in ceratopsians (e.g., Bakker 1987; Johnson and Ostrom 1995; Paul and Christiansen 2000). Upon removal of the ironstone from the frill, it became clear that this specimen represented a new taxon. The postcranial skeleton is presently being prepared and its anatomy and relevance to posture in ceratopsids will be the subject of a future publication. Two additional specimens (TMP 87.45.1 and TMP 98.102.8),

DOI: 10.1139/cjes-38-10-1423

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more recently recovered from the uppermost beds of the Dinosaur Park Formation, are referred to C. irvinensis. Institutional abbreviations AMNH, American Museum of Natural History, New York; ANSP, Academy of Natural Sciences, Philadelphia; MOR, Museum of the Rockies, Bozeman; OMNH, Oklahoma Museum of Natural History, Norman; NMC, Canadian Museum of Nature, Ottawa; TMM, Vertebrate Paleontology and Radiocarbon Laboratory, University of Texas, Austin; ROM, Royal Ontario Museum, Toronto; TMP, Royal Tyrrell Museum of Palaeontology, Drumheller; UAVP, University of Alberta, Calgary; KUVP, University of Kansas Museum of Natural History, Lawrence; YPM, Yale University Peabody Museum of Natural History, New Haven.

Systematic paleontology Order Ornithischia Seeley, 1888 Suborder Ceratopsia Marsh, 1890 Family Ceratopsidae Marsh, 1888 Subfamily Chasmosaurinae Lambe, 1915 Genus Chasmosaurus Lambe, 1914 Chasmosaurus irvinensis sp. nov. Holotype NMC 41357. Skull, largely complete, but fragmented; postcranial skeleton, articulated and nearly complete, except for the tail. Referred specimens TMP 87.45 1. Dorsoventrally crushed skull lacking mandible, most of the posterior parietal bar, most of the right squamosal, and distal tip of the right jugal. TMP 98.102.8. Fragmentary skull with nearly complete posterior parietal bar. Type Locality Located 4.2 km southwest of Irvine, Alberta, NE 1/4 section 23, T11, R3, west of the 4th meridian. Elevation approximately 795 m above sea level (ASL), Upper Dinosaur Park Formation (Eberth and Hamblin 1993). Detailed locality data on file at the Royal Tyrrell Museum of Palaeontology.

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Localities of referred specimens TMP 87.45.1; 4.8 km NW of Iddesleigh, Alberta, Upper Dinosaur Park Formation. TMP 98.102.8; near the village of Onefour, Southeastern Alberta, Upper Dinosaur Park Formation. Detailed locality data on file at the Royal Tyrrell Museum of Palaeontology. All specimens were found within 20 m of Lethbridge Coal Zone, from rock that is considered to be latest Dinosaur Park Formation (D.A. Eberth, personal communication, 2000).

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Diagnosis Chasmosaurine ceratopsid with transversely broad snout; nasal horn core short and transversely broad; brow horn absent, its normal position occupied by a low, raised, rugose boss, in one specimen bearing a large, smooth surfaced, hemispherical resorption pit; jugal notch on anterior squamosal broadly rounded and open (not parallel-sided);

squamosal tapers little posteriorly, subrectangular in outline, and projects almost directly laterally. Posterior parietal bar straight in anterior and dorsal aspects, projects only slightly posterior to the squamosal; maximum diameter of parietal fenestra less than length of preorbital region of the skull. Ten epoccipitals on posterior parietal bar, lateral epoccipital low and shield-shaped, the remaining eight nearly indistinguishably coossified together, and composed of flattened posteroventral laminae that wrap around the back of the bar, and larger laminae that curve strongly dorsally and anteriorly over the bar.

Description of NMC 41357 (holotype) The skeleton, virtually complete except for parts of the left side of the skull and most of the tail, is preserved in an upright, crouched posture in a coarse, poorly consolidated, light gray sandstone. The anterior part of the skull, portions of the ribcage, and pelvis were exposed to weathering prior to discovery; as a result, some of the ribs and parts of the pelvic girdle have fragmented, and portions of the snout were collected as float. Nevertheless, not all damage can be attributed to postexposure weathering. The frill had floated off to the left of its natural position before burial, disarticulating and displacing the syncervical and first free cervical vertebra. Much of the snout appears to have broken apart and scattered prior to burial. The quadrates, quadratojugals, and mandible were similarly displaced. The defleshed frill remained exposed on the channel bed long enough to accumulate a thick layer of organic debris, as a considerable quantity of carbonized plant material containing an isolated theropod tooth, gar scale, several nodules possibly representing coprolites, and caddisfly larva cases covered its dorsal surface and filled the parietal fenestrae. The fragmentary condition of the snout appears to be due to damage rather than incomplete ossification. Coossification of most elements is advanced, suggesting that the specimen was an adult at the time of death. Several characters, including replacement of supraorbital horn cores with resorption pits, presence of an infratemporal flange of the jugal, a parietosquamosal frill with a maximum transverse width greater than 2.5 times the interorbital width, and a deep median parietal bar (see characters 12, 13, 17, and 24 in Appendix 1) clearly place the specimen within the genus Chasmosaurus. However, many unique features of the skull indicate clearly that it is a new species. Measurements for the skull (Fig. 1) are recorded in Table 1. The postcranial skeleton, which is presently being prepared, will be considered in a future publication. Snout As in chasmosaurines generally, the snout is relatively long and dorsoventrally shallow, the length of the preorbital region being approximately 2.25 times the minimum depth of the snout between the orbit and nasal horn to the alveolar margin (Fig. 2). The strongly recurved rostral is not fused to the premaxilla. It is incomplete dorsally, but an excavation on the rugose convex dorsal portion of the coossified premaxillae indicates its dorsal extent. The thickened dorsal rim of the premaxilla had broken away from the remainder of the bone before discovery, and portions of the ÂŠ 2001 NRC Canada

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Fig. 1. Chasmosaurus irvinensis. (A) The measured dimensions of the skull (see Table 1). (B) Important features of the skull (see description). ang, angular; art, articular; corp, coronoid process of dentary; d, dentary; ec, facet for ectopterygoid; ep1–ep5, parietal epoccipitals one to five; epij, epijugal; ipmf, interpremaxillary formen; itf, infratemporal fenestra; itfj, infratemporal flange of the jugal; j, jugal; jn, jugular notch; mx, maxilla; n, nasal; p, parietal; pd, predentary; pf, parietal fenestra; pff, postfrontal fontanelle; pm, premaxillary; pmfl, premaxillary flange; ppb, palpebral; q, quadrate; qj, quadratojugal; r, rostral; rpit, resorption pit; sa, surangular; sq, squamosal; stf, supratemporal fenestra.

premaxillary septum have been lost. Diverging lateral surfaces surrounding a posteriorly facing, medial pocket on the posterior edge of a preserved portion of the septum indicate that a hollow nasal strut was present. Only the ventral portion of the premaxillary flange is preserved, so it is not possible to determine whether it was developed only ventrally, as in Pentaceratops, or extends the full height of the septum, as in other species of Chasmosaurus. The posterodorsal margin of a modest interpremaxillary fenestra is preserved anteriorly. The premaxilla forms the anterior and ventral margin of the external naris. In both premaxillae, The posteroventral processes are incomplete, but the broken posterior end of each process bears a notch, flanked on either side by broken bone, indicating that it terminated in a forked projection set into the nasal as in other species of Chasmosaurus and Pentaceratops (Forster et al. 1993). The nasal bones have completely coossified. The short nasal horn core is located directly over the naris, distinctly forward of the horn core position in Chasmosaurus mariscalensis (Forster et al. 1993), C. russelli, and C. belli (Godfrey and Holmes 1995). It is much shorter than that of Pentaceratops (Wiman 1930), and the transverse dimension of its broadly eliptical cross section (Fig. 3) is proportionately greater than that of any other specimen of Chasmosaurus. There is no evidence of a separate epinasal ossification. Immediately anterior to the horn core and separated from it by a distinct constriction, the nasal forms a rugose swelling. The anterior end of the nasal is broken and some bone is missing, but an excavation on the right lateral surface of the thickened dorsal margin of the coossified premaxillae indicates that the premaxillae were clasped between anterolateral laminae of the nasal as in Chasmosaurus belli and C. russelli (Godfrey and Holmes 1995) in contrast with the condition in C. mariscalensis (Forster et al. 1993). Posterior to the horn core, the nasal widens considerably to produce a snout noticeably wider in dorsal view than that in other chasmosaurines. As preserved, the right maxilla bears 21 alveoli, most occupied by teeth, and the left maxilla 24 or 25 alveoli. Although neither element is complete anteriorly, spacing of the teeth indicates that a complete maxilla would bear approximately 28 teeth. The posterior (“free”) portion of each maxilla bears a small, oval scar on its lateral surface for articulation with the ectopterygoid. Anteriorly, the lateral surface of the maxilla turns dorsolaterally. However, the external body of the maxilla is not preserved. It is clear, however, from the preserved morphology, that as in most chasmosaurines, except possibly Chasmosaurus mariscalensis

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(but see Forster et al. 1993), its dentigerous portion was strongly inset from the body of the maxilla. 25

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Table 1. Skull measurements (mm) of TMP 87.45.1 and NMC 41357. 75

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Maximum frill width Frill length from back of jugular notch – posterior margin of parietal Back edge of jugular notch – posterior end of squamosal (L/R) Posterior edge of epijugal – posterior edge of squamosal Total midline length Posterior margin of postfrontal fontanelle – posterior margin of parietal (curved surface) length of frontal fontanelle Anterior margin of supratemporal fenestra – anterior margin of parietal fenestra Parietal fenestra width Parietal fenestra (maximum anteroposterior length, L/R) Maximum squamosal width (curved surface) Minimum squamosal width at jugular notch (curved surface) Posterior edge of quadrate condyle – anterior end of rostral Anterior end of epijugal – anterior end of rostral Anterior margin of orbit – anterior end of rostral Minimum snout depth to alveolar margin (est.) Anterior margin of orbit – posterior margin of naris Dorsal margin of naris – dorsal tip of nasal horn core Transverse width of nasal horn core base (max.) Maximum anteroposterior length of nasal horn core Maximum transverse width of nasals Maximum diameter of orbit Rim of orbit – ventral edge of epijugal Rim of infratemporal fenestra – ventral edge of epijugal Orbital margin – infratemporal fenestra Maximum diameter of infratemporal fenestra Minimum interorbital distance Length of predentary Length of dentary

TMP 87.45.1

NMC 41357

1020 685 (L) 625/— 805 1375 610?

1050 750 (R) 680/700 850 1410 840

145 ?245 (L)

180 435 (R)

250–310 (L, min.–max.) 260/—(est.) 355 (at 1st epoccipital) 250 (distorted) (distorted) 575 — 185 115 84 158 — 99/81 (L/R) (distorted) 140 (distorted) 89 270 — —

370/390 (max. L/R) 265/325 300 265 820 780 610 240 205 115 80 125 221 105 (R) 285 135 140 80 300 290 430

Note: Unless otherwise indicated, the values represent the shortest distance as measured by calipers. est., estimated; L, left; R, right, max., maximum; min., minimum.

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by fusion. Postmortem crushing has distorted part of the dorsal rim of the orbit. The dorsal end of the right palpebral has been separated from the postorbital and rotated ventrally, distorting the anterior margin of the orbit. In the position normally occupied by the brow horn, the postorbital bears a smooth, dorsally facing semicircular pocket set in a low boss located directly over the centre of the orbit. As in Styracosaurus albertensis (NMC 344) and Einiosaurus (e.g., MOR 456; Sampson et al. 1997), and to some extent at least one specimen of Chasmosaurus (NMC 8800), this pocket presumably represents the position of a resorbed horn core. Medially, the postorbital bounds the right half of an unusually wide keyhole-shaped postfrontal fontanelle (Fig. 3). It opens into a supracranial cavity, the lateral contours of which reflect the outline of the fontanelle, being narrow posteriorly and widening anteriorly to a maximum of 20 cm transverse width. The cavity does not underlie the supraorbital boss, and there is no evidence of an extensive cranial sinus system. Temporal region The coossified jugal and squamosal are incomplete ventral to the infratemporal fenestra. The curved dorsal edge of the quadratojugal appears to form part of the ventral margin of

the fenestra. However, the lateral surface of this bone is damaged, making it impossible to determine whether a posterior flange of the jugal passed lateral to the quadratojugal to contact the squamosal, as in Chasmosaurus belli, C. russelli, and Pentaceratops, or whether a portion of the fenestral margin of the quadratojugal is exposed laterally between the jugal and squamosal as in other chasmosaurines, including C. mariscalensis. The fenestra, like that of Chasmosaurus mariscalensis and Pentaceratops, is large for a ceratopsid, with its maximum diameter at least 75% of that of the orbit. Posterodorsal to the infratemporal fenestra, the squamosal is pierced by a small round hole (Fig. 4). The regular shape and thick, smooth, bevelled margin of this hole are not readily explained as bone resorption or a pathological condition. Fragments of the incomplete right epijugal are firmly sutured to the jugal. As in most other ceratopsids, the squamosal, quadratojugal, and quadrate are not coossified.

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Frill The frill is nearly complete, lacking only part of the anterior parietal between the supratemporal fenestra and anterior portions of the squamosals. The most distinctive features of this specimen are associated with the frill. As in other species of Chasmosaurus, and in contrast to almost all other © 2001 NRC Canada

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Fig. 2. Chasmosaurus irvinensis sp. nov. Lateral view of the skull. (A) NMC 41357, elements placed in approximate articulation. (B) Reconstruction. Scale bar = 10 cm.

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ceratopsids, the maximum width of the frill (1050 mm) exceeds 2.5 times the interorbital width (300 mm). However, the proportions and general appearance of the frill otherwise are quite distinct from that of any known chasmosaurine. Unlike Chasmosaurus belli and C. russelli, but as in C. mariscalensis, the free border of the squamosal is gently

convex rather than concave (Fig. 3). However, unlike in C. mariscalensis, where the squamosal forms a vertical plate, the free border is rolled strongly laterally. As a consequence, much of the morphological lateral surface faces approximately dorsally, and the bone presents a thin lateral profile, except at its anterior end (Fig. 2). Anteriorly, its free edge forms the ÂŠ 2001 NRC Canada

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Fig. 3. Chasmosaurus irvinensis sp. nov. Dorsal view of the skull. (A) NMC 41357, elements placed in approximate articulation. (B) Reconstruction. Scale bar = 10 cm.

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posterior and dorsal portions of a wide, open “jugal notch” distinct from the parallel-sided, quadrangular embayment seen in all other species of Chasmosaurus and most other ceratopsids. Another striking feature of the squamosal is the bluntly truncated posterior end, resulting in an elongate, rectangular profile that contrasts sharply with the triangular, acutely attenuated squamosal of Chasmosaurus belli and C. russelli or the sickle-shaped squamosal of C. mariscalensis. Although the frill was separated from the rest of the skull and portions of its anterior end have been lost, its position and orientation relative to the anterior part of the skull can be established by referring to the position of the apparently undistorted quadrate facet on the right squamosal. When articulated with the right quadrate and cheek unit, the frill projects posterodorsally at an angle of between 45 and 50° to the horizontal, a more vertical orientation than in either Chasmosaurus belli or C. russelli (approximately 20–25°), but still somewhat less than in C. mariscalensis (about 60°). The straight posterior and median parietal bars meet at right angles to form a “T” (Figs. 3, 5). Consequently, as in C. belli, a median embayment is lacking, and the parietals do not project significantly posterior to the squamosals. As in other species of Chasmosaurus, the posterior bar is narrow due to the greatly enlarged parietal fenestrae. However, in contrast with other species of Chasmosaurus, in which the bar is reasonably stout with a flat dorsal surface (Forster et

al. 1993), the bone is very thin in this region (averaging about 5 mm), and rolls up along its posterior margin to form a strongly concave dorsal surface. Measured along this curved surface, the posterior bar measures from 12 to 14 cm anteroposteriorly. The frill shows several pronounced asymmetries. The left parietal bar is continuous along its contact with the squamosal, excluding the latter from forming any part of the parietal fenestra. Throughout its length, it is thickest dorsoventrally at its suture with the squamosal and thins to a sharp, horizontal lamina that faces the fenestra. The right side of the parietal resembles the left anteriorly, but posteriorly, the medially projecting lamina subsides, and behind this the bar is represented by a thin, convex strap that appears to end just before reaching the posterior end of the parietal. This leaves the squamosal to form about 5 cm of the posterolateral margin of the right parietal fenestra. The median parietal bar is also asymmetric. A thin lamina projects into the fenestra from its left side, but an equivalent lamina is absent on the right side. The median parietal bar is depressed below the level of the lateral edge of the frill, producing a flat or even slightly dorsally concave shield in coronal section. In contrast, in all other ceratopsids, the median portion of the parietal frill is raised relative to its lateral edges to form a dorsally convex shield in coronal section. In other species of Chasmosaurus © 2001 NRC Canada

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Fig. 4. Chasmosaurus irvinensis sp. nov. Hole of unknown origin in right squamosal. itf, infratemporal fenestra. Scale bar = 5 cm.

Fig. 5. Chasmosaurus irvinensis sp. nov. Anterior view of the skull. (A) NMC 41357, elements placed in approximate articulation. (B) Reconstruction. Scale bar = 10 cm.

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and Pentaceratops, the greatest dimension of their anteroposteriorly elongate parietal fenestrae exceed the preorbital length of their skulls. In NMC 41357, the greatest dimension of the parietal fenestrae is the transverse diameter, which clearly falls short of its preorbital length. Initial examination gives the impression that the frill is relatively short for Chasmosaurus. However, specific comparison with Chasmosaurus russelli (NMC 2280) permits refinement of this observation. Although basal length cannot be determined for NMC 41357, comparison of a number of dimensions of the snout and cheek (Table 1) with NMC 2280 (Godfrey and Holmes 1995, table 1), demonstrates that NMC 2280 is approximately 10% smaller. Thus, the parietal length, as measured along the curved surface from the posterior edge of the frontal fontanelle to the posterior edge of the frill (740 mm in NMC 2280; 840 mm in NMC 41357) is proportionately the same for these two specimens. However, a few marked differences in proportions contribute to the impression of a shorter frill in NMC 41357. The squamosal of the latter, as measured from the back of the epijugal to its posterior end, measures 850 mm, only 10 mm longer than NMC 2280. This, in combination with the straight posterior bar of NMC 41357, results in a frill that is proportionately slightly shorter overall. Nevertheless, the visual effect is more striking than the numbers would suggest. The squamosal bears seven or possibly eight low, triangular epoccipitals that are almost completely coossified, but can be identified by the possession of fine, parallel ridges distinct from the texture of the surrounding bone. The parietal bears 10 epoccipitals on its posterior margin rather than six, which

is the number in all other known chasmosaurines, except Triceratops (seven). The most lateral epoccipital on each side is stout, shield-shaped, and forms a firm, broad attachment to the bar adjacent to the parietal–squamosal suture. The remaining eight epoccipitals attach to the posterior margin of the bar, but unlike the lateral elements, each forms two thin laminae that diverge from the surface of the bar, one curling anterodorsally, the other anteroventrally (Fig. 6). The ventral lamina is more modestly developed, but can be distinguished clearly from the parietal by a deep furrow. Dorsally, the much larger laminae thin rapidly distally and curve to terminate in anteriorly projecting, subtriangular or quadrangular plates that overlap the posterior margins of the parietal fenestra in a manner somewhat reminiscent of the condition in Centrosaurus (e.g., Parks 1921, plate 1: “anterior process of frill”). The median epoccipital pair in Pentaceratops, although more modest in size, also curve anteriorly over the parietal (Lehman 1998), and a similar condition, albeit in an incipient state, appears to occur in Chasmosaurus russelli (NMC 2280, Godfrey and Holmes 1995). Another unusual feature of the epoccipitals is that, with the exception of the lateral pair, all have coossified © 2001 NRC Canada

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Fig. 6. Chasmosaurus irvinensis. nov. sp. Details of right epoccipital 4. Scale bar = 5 cm.

almost indistinguishably with one another in contrast to other chasmosaurines, in which the epoccipitals are discrete elements. Lower Jaw The lower jaws are virtually complete, except for parts of the right dentary. The dentary is relatively shallow compared with that of Chasmosaurus belli or C. russelli, and the surangular is not as robust (Fig. 2). The predentary is unusually large, comprising about 45% of the total length of the ramus.

Description of TMP 87.45.1 (referred specimen)

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This specimen (Figs. 7, 8) comprises a dorsoventrally crushed skull lacking the mandible, most of the right squamosal, distal portion of the right jugal, right lateral parietal bar, and most of the median and posterior parietal bars. It has been referred previously to the genus Chasmosaurus, but was considered indeterminate at the species level (Godfrey and Holmes 1995), because the portions of the frill showing most of the diagnostic features separating Chasmosaurus belli and C. russelli are not preserved. The skull is slightly smaller than NMC 41357, but shows adult bone texture (Sampson et al. 1997) on the postorbitals, left squamosal, and preserved portions of the parietal. A closely adhering layer of mudstone–sandstone was removed only with difficulty, resulting in significant damage to much of the bone surface. Before preparation could begin, it was necessary to reinforce the poorly preserved ventral surface of the skull and cover it in a layer of plaster, rendering this aspect inaccessible. Nevertheless, enough information is available to permit an outline reconstruction to be drafted (Fig. 9).

Snout The premaxillary fossa is pierced by a fenestra, but because only its anterior edge is preserved, its size and shape can only be estimated. The premaxillary strut is complete and bears a posteriorly projecting flange that extends its full length. Both maxillae have folded under the skull and are not accessible. The posterior portion of the snout has been compressed dorsoventrally, but there is no indication that this region of the skull differs significantly from that of NMC 41357. The undistorted nasal horn core is virtually identical in form and size to that of NMC 41357, but it is centred over the posterior margin of the naris rather than directly over it.

Circumorbital region Although the orbits have been compressed dorsoventrally, their dorsal margins have not been distorted significantly, allowing a reasonable estimate of their original curvature (Fig. 9). As in NMC 41357, the broad interorbital region lacks postorbital horn cores. Dorsal and slightly posterior to each orbit and around its lateral margin, the raised bone surface bears deep furrows running approximately perpendicular to the orbital margin. These furrows grade medially into shallow grooves that curve posteriorly toward the frontal fontanelle. Posterior to this, the dorsal surface of the postorbital bears a low, rounded swelling. At least four progressively smaller, smoother bumps are arranged posterior to this in a linear series along the dorsal edge of the squamosal. The bone is poorly preserved in the region of the frontal fontanelle, but enough of its edge is preserved to suggest that it was “keyhole”-shaped as in NMC 41357. Temporal region As a consequence of dorsoventral compression, the quadrates have rotated around their dorsal articulation with the squamosals into the horizontal plane, resulting in an unnaturally anterior placement of the quadrate condyles and a splaying of the cheeks laterally and anteriorly. This has resulted in some dorsoventral foreshortening of the jugals and compression of both the orbits and infratemporal fenestra, but there is no evidence that this region differs significantly from that of NMC 41357. The jugal projects ventral to the infratemporal fenestra as a tapering wedge that appears to contact the squamosal posteriorly, excluding the quadratojugal from the margin of the fenestra as in Chasmosaurus belli and C. russelli. Frill The frill has been compressed and rotated ventrally relative to the remainder of the skull, separating the parietal from its contact with the frontals. The anterior portion of the median parietal bar is preserved. It expands laterally to form the floor of the supratemporal fenestra on each side. A number of shallow grooves fan out from the posterior edge of the supratemporal fenestra across the parietal to the margin of the parietal fenestra. As in NMC 41357, the strap-like left lateral parietal bar bears a lamina of bone that projects medially into the parietal fenestra. The bar is continuous, excluding the squamosal from forming any part of the fenestra. The preserved posterior and lateral margins of the left parietal fenestra indicate that, as in NMC 41357, its long axis is © 2001 NRC Canada

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Fig. 7. Chasmosaurus irvinensis sp nov. Lateral view of TMP 87.45.1. Scale bar = 10 cm. 75

Fig. 8. Chasmosaurus irvinensis sp. nov. Anterior view of TMP 87.45.1. Scale bar = 10 cm.

well-preserved triangular epoccipital lies directly medial to this point. Although it is unlike the epoccipital of any other known chasmosaurine, it is very similar in its size, shape, and texture to the epoccipital occupying the equivalent position in NMC 41357. The complete left squamosal bears seven epoccipitals. The anterior edge of the squamosal is angled more sharply anteriorly than in NMC 41357, producing a narrower, more quadrangular jugular notch. More posteriorly, between epoccipitals two and three, the lateral edge of the squamosal bears an additional notch that has no equivalent in any known ceratopsid. Whether it represents a pathology is uncertain, but its presence may be correlated with the strongly reflected angle of the anterior edge of the squamosal. As is NMC 41357, the lateral edge of the squamosal is convex.

Description of TMP 98.102.8 (referred specimen)

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transversely oriented, and although slightly larger than in NMC 41357, the fenestra was nevertheless much smaller than in any other species of Chasmosaurus. Only the left lateral corner of the posterior parietal bar is preserved. An oval facet immediately medial to its suture with the squamosal marks the position of the most lateral parietal epoccipital, presumably lost before collection of the specimen. A large,

This skull comprises several hundred fragments, the positions of many of which cannot be determined. However, it was possible to restore the posterior parietal bar, with the exception of its central portion (Fig. 10). The bar, with an estimated width of about 1060 mm, is straight and meets the preserved portions of lateral bars at right angles, as in NMC 41357. Although the most medial epoccipital (here designated one) and the most lateral (five) are not preserved on either side, it is clear that a total of 10 epoccipitals were present in life. Among ceratopsids, this epoccipital count is shared only by NMC 41357. All preserved epoccipitals are large (measured mediolaterally, epoccipitals two, three, and four on the right side are 110+, 130, and 109 mm, respectively; on the left side, epoccipitals three and four are 135 mm and 105 mm, respectively) and have dorsal laminae that curl anterodorsally (although not as sharply as in NMC 41357) from the posterior edge of the parietal bar. As in NMC 41357, epoccipital four is roughly triangular and at its apex projects at about 90Â° to the plane of the dorsal surface of the posterior parietal bar. The more medial epoccipitals are roughly rectangular in proportions, and project more directly anteriorly, with epoccipital three oriented at about 60Â° to the ventral surface, and epoccipital two projecting at a slightly lower angle. As in NMC 41357, the dorsal surfaces of the epoccipitals have a rugose texture, and bear numerous, small ÂŠ 2001 NRC Canada

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Fig. 9. Chasmosaurus irvinensis sp. nov. Reconstruction of TMP 87. 45.1 in (A) anterior; (B) lateral; (C) dorsal. When only one side is preserved, bilateral symmetry is assumed. Scale bar = 10 cm.

their bases and are more or less separated by ringlike constrictions, conspicuous on the anterior, dorsal, and posterior surfaces but only faintly developed on the ventral surface of the parietal bar. The ventral laminae of the epoccipitals in TMP 98.102.8 are much less conspicuous, being separated from the smooth laminar bone of the parietal by only a shallow furrow. The posterior parietal bar of TMP 98.102.8, although similar to that of NMC 41357 in most respects, is noticeably more robust. The bar is somewhat thicker, being about 13 mm thick at the base of the epoccipital and tapering to a bluntly rounded edge of about 5 mm in thickness.

Discussion

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foramina, presumably for blood supply to the germinal epithelium of the horny material that covered these structures in life. The posterior surface of the parietal bar bears a furrow along the ventral edges of the epoccipitals. Several foramina pass into this furrow from a lateral to medial direction. These may be contiguous with a central space visible on the broken ends of the bar, but this cannot be confirmed. Although TMP 98.102.8 shares many similarities with NMC 41357, there are some differences. The epoccipitals are much thicker, especially at their bases. In contrast with NMC 41357, the epoccipitals are not as clearly coalesced at

Chasmosaurus irvinensis shows several striking apomorphies, such as the loss of the postorbital horn cores, (character 10, see Appendix 1), straight posterior parietal bar (character 20), reduced, transversely oriented, posteriorly placed parietal fenestrae (character 21), and 10 parietal epoccipitals (character 28), eight of which curve anterodorsally (character 30). The small, posteriorly placed parietal fenestrae are unique within the clade comprising Chasmosaurus and Pentaceratops and are here interpreted as a reversal to the primitive condition. The presence of 10 parietal epoccipitals represents a unique condition within ceratopsids. When these unusual features of NMC 41357 first became evident, most observers felt that the morphological distance between this specimen and other chasmosaurines justified the erection of a new genus to receive it (e.g., Holmes et al. 1999). Although future discoveries may yet confirm this subjective impression, currently available data does not support it. The present phylogenetic analysis places the taxon securely within the genus Chasmosaurus. Four species of Chasmosaurus have been recognized in recent years by other researchers: C. belli, C. russelli, and C. canadensis, all from Alberta, and C. mariscalensis from Texas (Dodson and Currie 1990; Lehman 1990). In a study of Chasmosaurus cranial material from the Dinosaur Park Formation of Alberta, Godfrey and Holmes (1995) reassigned C. canadensis as a junior synonym of C. belli, but retained both C. belli and C. russelli. Lehman (1998) disagreed, suggesting instead that the characters used by Godfrey and Holmes to define these species are highly variable within Chasmosaurus and do not show discrete states. Lehman further postulated that these taxa are best regarded as an intraspecific morphocline and recognized only two species, Chasmosaurus mariscalensis from Texas, and C. belli from Alberta. Based on a reexamination of specimens, as well as the results of the phylogenetic analysis presented here, we consider both Canadian species, C. belli and C. russelli, to be valid. Stratigraphic occurrence of specimens identifiable to species is consistent with this conclusion. Godfrey and Holmes (1995), based on admittedly limited stratigraphic data, suggested that Chasmosaurus russelli and C. belli might be stratigraphically distinct, with the former being confined to the lower, and the latter being confined to the upper part of the Dinosaur Park Formation. Recent work carried out by Philip J. Currie and others, including one of the authors (MJR), has resulted in the relocation of most of the significant dinosaur quarries within Dinosaur Park. Accurate stratigraphic data show that specimens referrable to ÂŠ 2001 NRC Canada

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Fig. 10. Chasmosaurus irvinensis sp. nov. Dorsal view of posterior parietal bar of TMP 98.102.8. Scale bar = 10 cm. ep2, second epoccipital from the midline; ep3, third epocciptal from the midline; ep4, fourth epoccipital from the midline.

Fig. 11. Relative stratigraphic position of species of Chasmosaurus in Alberta. The stratigraphic column is based on that for Dinosaur Provincial Park, where TMP 87.45.1 was collected. The Lethbridge Coal Zone is time transgressive across the province of Alberta. Consequently, both NMC 41357 and TMP 98.102.8, which were collected outside Dinosaur Provincial Park, may have been preserved in beds equivalent in age to the Lethbridge Coal Zone within the Park. This possibility is indicated by the dashed line and question mark extending into the Lethbridge Coal Zone. BF, Bearpaw Formation; C., Chasmosaurus.

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Chasmosaurus russelli (NMC 8800) and C. cf. russelli (TMP 81.19.175) come from near the base of the Dinosaur Park Formation (with an elevation of 658 and 670 m ASL, respectively), whereas those referrable to C. belli (NMC 2245, ROM 839, ROM 843, YPM 2016) were found significantly higher in the section (ranging from 676 to 692 m ASL; see Fig. 11). Other specimens of Chasmosaurus that have yet to be prepared, or whose quarry location has yet to be determined, can potentially test this hypothesis. The distribution of C. russelli and C. belli is parallelled by that of Centrosaurus apertus and Styracosaurus albertensis, with the former, like Chasmosaurus russelli, confined to the lower part of the Formation, and the latter, like C. belli, confined to the upper portion of the Formation (Ryan et al. 1998). This suggests that the temporal replacement of Chasmosaurus russelli with C. belli may have been part of a faunal turnover also involving Centrosaurus apertus and Styracosaurus albertensis. In this connection, it is important to note that NMC 41357 came from a layer within 20 m of

the Lethbridge Coal Zone (795 m ASL) and well above either of the other Canadian Chasmosaurus species. The other two known specimens of Chasmosaurus irvinensis also came from the uppermost Dinosaur Park Formation, within 20 m and 10 m, respectively, of the Lethbridge Coal Zone (Fig. 11). There is no evidence for stratigraphic overlap among the three species. Only two limited phylogenetic analyses have dealt with species-level resolution in Chasmosaurus. Forster et al. (1993; five ingroup taxa, 9 characters) included C. belli, C. russelli, C. mariscalensis, and Pentaceratops. Their analysis supported the monophyly of Chasmosaurus, with C. russelli and C. belli regarded as sister taxa. Lehman (1996) analyzed species-level relationships among chasmosaurines (nine ingroup taxa, 14 characters), including C. mariscalensis, C. belli, and “C. canadensis.” This analysis suggested that Chasmosaurus was a paraphyletic taxon (Lehman 1996, fig. 10). To construct a hypothesis of the phylogenetic relationships of Chasmosaurus irvinensis to other chasmosaurines, and in particular other species of Chasmosaurus, we performed a cladistic analysis using 30 cranial characters (Appendix 2). Six additional ingroup taxa were analyzed, including Chasmosaurus belli, C. russelli, C. mariscalensis, Pentaceratops, centrosaurines, and “other chasmosaurines” (Anchiceratops, Arrhinoceratops, Diceratops, Torosaurus, Triceratops). Characters were polarized using Protoceratops and Zuniceratops. The coding for “outgroup” in our matrix is a combination of the codings for both of these taxa. All characters were binary, except for character 16, which was left unordered. All characters were equally weighted and optimized using delayed tranformations. The data matrix was analyzed using the Exhaustive Search option in Phylogenetic Analysis Using Parsimony (PAUP, version 3.50) and manipulated in MacClade (version 3.05). Polymorphisms are interpreted by PAUP as uncertainties. Three most parsimonious trees of 40 steps resulted from this analysis (consistency index (CI) = 0.775, CI excluding uniformative characters = 0.679; retention index (RI) = 0.719). The strict consensus tree is shown in Fig. 12. The three trees differ from one another only in the placement of Chasmosaurus mariscalensis, which is either the sister-taxon to Pentaceratops, the sister taxon to a (C. russelli (C. belli + C. irvinensis)) clade, or the sister-taxon to a Pentaceratops (C. russelli (C. belli + C. irvinensis)) clade. In all three trees, a sister-group relationship between Chasmosaurus irvinensis and C. belli is supported by two unambiguous characters (18 and 29). The clade (Chasmosaurus russelli (C. belli + C. irvinensis)) is supported by four characters, although only one (24) is unambiguous. © 2001 NRC Canada

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Fig. 12. Phylogenetic interrelationships of chasmosaurines. For a discussion of the characters indicated on the cladogram, see Appendix 1. C., Chasmosaurus.

chasmosaurine phylogeny. The placement of C. mariscalensis should be evaluated in the context of a larger and more thorough phylogenetic analysis of Chasmosaurinae.

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Two of these characters (12 and 13) are shared with centrosaurs (homoplasies). The fourth character (17), shared with Protoceratops, is interpreted as a reversal. The analysis strongly supports the placement of the new species within the genus Chasmosaurus, since it requires four additional steps to move it outside of Pentaceratops. Pentaceratops and Chasmosaurus are supported as sister-taxa by eight characters (2, 5, 6, 16, 21, 22, 23, and 25), only two of which (5 and 21) are ambiguous. It requires six additional steps to move Pentaceratops to its more traditional position as the sister-group of other chasmosaurines (e.g., Forster 1990; Lehman 1996). Dodson and Currie (1990) have also hypothesized a sister-group relationship between Chasmosaurus and Pentaceratops. However, in their analysis, the Chasmosaurus–Pentaceratops clade was placed within our other chasmosaurines between Anchiceratops and a (Triceratops (Arrhinoceratops + Torosaurus)) clade. Our analysis suggests that the position of C. mariscalensis is somewhat unresolved. Although this is not the result of character conflict, but rather of missing data, it still raises the possibility that C. mariscalensis may be more closely related to Pentaceratops than to the Canadian Chasmosaurus species. Although one of the three most parsimonious trees does place C. mariscalensis as the sister-taxon to all other species of Chasmosaurus, three additional steps are required to move this taxon within Chasmosaurus (that is, as the sister-taxon to any of the other three species). This reflects the fact that C. mariscalensis lacks all but one character (3, septal flange bordering the entire caudal margin of narial strut) of the five characters (3, 12, 13, 17, 24) that unite the Canadian Chasmosaurus species. Of possible significance is that Pentaceratops and Chasmosaurus mariscalensis are both, as far as is known, restricted to the southwestern part of North America and are well separated geographically from the more northerly Canadian species of Chasmosaurus. No other ceratopsid genus (with the exception of Torosaurus, which ranges from Canada to Texas), has such an extensive geographic distribution. Although it is intriguing to consider Pentaceratops and Chasmosaurus mariscalensis as sister taxa, it would be unwise to consider the possibility further on the basis of the present analysis. We emphasize that the characters and taxa for this analysis were chosen specifically to determine the relationships of Chasmosaurus irvinensis to other species of Chasmosaurus, and therefore this analysis is not meant to be a robust analysis of

We would like to thank the late Mr. William Yanke for permission to excavate on his land, and the late Harold Sherman and the late Harvey Champagne, who helped Dr. Wann Langston collect NMC 41357. Thanks again to Dr. Langston for sharing information on the collection of this specimen. Expert preparation was provided by Cao Qiang and Clayton Kennedy on NMC 41357 (thank you to the latter for his help in piecing together the skull), and Wendy Sloboda on TMP 87.45.1 and 98.102.8. Photographs of NMC 41357 were provided by Martin Lipman. Dr. Alison Murray prepared the figures for electronic submission. We would like to thank Dr. Dale Russell for bringing NMC 41357 to our attention, and Drs. Peter Dodson and Scott Sampson, who discussed this specimen with us on several occasions, and shared many useful insights. Finally, we would like to thank Drs. Peter Dodson and Peter Makovicky for reviewing the manuscript and providing many helpful comments.

References Bakker, R.T. 1987. The return of the dancing dinosaurs. In Dinosaurs past and present, Vol. 1, Edited by S.J. Czerkas and E.C. Olson. Natural History Museum of Los Angeles County, Los Angeles, Calif., pp. 38–69. Brown, B., and Schlaikjer, E.M. 1940. The structure and relationships of Protoceratops. Annals of the New York Academy of Sciences, 40: 133–266. Cope, E.D. 1876. Descriptions of some vertebrate remains from the Fort Union beds of Montana. Proceedings of the Academy of Natural Sciences of Philadelphia, 28: 248–261. Dodson, P., and Currie, P.J. 1990. Neoceratopsia,. In The Dinosauria. Edited by D. Weishampel, P. Dodson and H. Osmolska. Berkeley, University of California Press, Los Angeles, Calif., pp. 593–618. Eberth, D.A., and Hamblin, A.P. 1993. Tectonic, stratigraphic, and sedimentologic significance of a regional discontinuity in the Upper Judith River group (Belly River wedge) of southern Alberta, Saskatchewan, and northern Montana. Canadian Journal of Earth Sciences, 30: 174–200. Forster, C.A. 1990. The cranial morphology and systematics of Triceratops, with a preliminary analysis of ceratopsian phylogeny. Unpublished PhD dissertation, University of Pennsylvania, Philadelphia, Pa. Forster, C.A. 1996. New information on the skull of Triceratops. Journal of Vertebrate Paleontology, 16: 246–258. Forster, C.A., Sereno, P.C., Evans, T.W., and Rowe, T. 1993. A complete skull of Chasmosaurus mariscalensis (Dinosauria: Ceratopsidae) from the Aguja Formation (late Campanian) of West Texas. Journal of Vertebrate Paleontology, 13: 161–170. Godfrey, S.J., and Holmes, R. 1995. Cranial morphology and systematics of Chasmosaurus (Dinosauria: Ceratopsidae) from the Upper Cretaceous of western Canada. Journal of Vertebrate Paleontology, 15: 726–742. Holmes, R., Shepherd, K., Forster, C. 1999. An unusual chasmosaurine ceratopsid from Alberta. Journal of Vertebrate Paleontology, 19(suppl. to No. 3): 52A. © 2001 NRC Canada

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Johnson, R.E., and Ostrom, J.H. 1995. The forelimb of Torosaurus and an analysis of the posture and gait of ceratopsians. In Functional morphology in vertebrate paleontology. Edited by J. Thomason. Cambridge University Press, New York, pp. 205–218. Lehman, T.M. 1989. Chasmosaurus mariscalensis, SP. NOV., an new ceratopsian dinosaur from Texas. Journal of Vertebrate Paleontology, 9: 137–162. Lehman, T.M. 1990. The ceratopsian subfamily Chasmosaurinae: sexual dimorphism and systematics. In Dinosaur systematics— approaches and perspectives. Edited by K. Carpenter and P.J. Currie. Cambridge University Press, New York, pp. 211–229. Lehman, T.M. 1996. A horned dinosaur from the El Picacho Formation of West Texas, and a review of ceratopsian dinosaurs from the American Southwest. Journal of Paleontology, 70: 494–508. Lehman, T.M. 1998. A gigantic skull and skeleton of the horned dinosaur Pentaceratops sternbergi from New Mexico. Journal of Paleontology, 72: 894–906. Marsh, O.C. 1889. Notice of new American Dinosauria. American Journal of Science, (series 3), 37: 331–336. Maryañska, T., and Osmólska, H. 1975. Protoceratopsidae (Dinosauria) of Asia. Palaeontologia Polonica, 33: 133–181. Parks, W.A. 1921. The head and forelimb of a specimen of Centrosaurus apertus. Transactions of the Royal Society of Canada (series 4), 15: 53–63. Parks, W.A. 1925. Arrhinoceratops brachyops, a new genus and species of Ceratopsia from the Edmonton Formation of Alberta. University of Toronto Studies, Geological Series, 19: 5–15. Paul, G., and Christiansen, P. 2000. Forelimb posture in neoceratopsian dinosaurs: implications for gait and locomotion. Paleobiology, 26: 450–465. Ryan, M.J., Eberth, D.A., Brinkman, D.A., and Russell, A.P. 1998. A sub-adult Styracosaurus (Ornithischia) from the Dinosaur Park Formation (Late Campanian), Alberta, Canada. Journal of Vertebrate Paleontology, 18 (supplement): 73A. Sampson, S.D. 1995. Two new horned dinosaurs from the Upper Cretaceous Two Medicine Formation of Montana; with a phylogenetic analysis of the Centrosaurinae (Ornithischia: Ceratopsidae). Journal of Vertebrate Paleontology, 15: 743–760. Sampson, S.D., Ryan, M.J., and Tanke, D.H. 1997. Craniofacial ontogeny in centrosaurine dinosaurs (Ornithischia: Ceratopsidae): taxonomic and behavioral implications. Zoological Journal of the Linnaean Society, 121: 293–337. Sternberg, C.M. 1940. Ceratopsidae from Alberta. Journal of Paleontology, 14: 468–480. Wiman, C. 1930. Uber Ceratopsia aus der Oberen Kreide in New Mexico. Nova Acta Regiae Societas Scientarum Upsaliensis, 7: 1–19.

Appendix 1. Characters used in phylogenetic analysis 100

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(1) Premaxilla, narial strut (Forster et al. 1993): absent (0); present (1). The narial strut, a well-defined thickening in the posterior portion of the premaxillary septum, is found in all chasmosaurines, but is absent in centrosaurines and outgroup taxa. (2) Premaxilla, septal flange (Forster et al. 1993): absent (0); present (1). The septal flange is a thin lamina of bone along the posterior margin of the narial strut. The septal flange is present in all species of Chasmosaurus (e.g., NMC 2280),

including C. irvinensis, and Pentaceratops (e.g., AMNH 6325). The septal flange is absent in centrosaurines and all other chasmosaurines. (3) Premaxilla, septal flange length (Forster et al. 1993): spans entire posterior margin of narial strut (0); restricted to ventral portion of narial strut (1). In Chasmosaurus belli, C. russelli, C. mariscalensis, and C. irvinensis, the septal flange borders the entire posterior margin of the narial strut. The septal flange is restricted to the ventral half of the narial strut in Pentaceratops (e.g., AMNH 6325). Character states are randomly assigned.

(4) Premaxilla, septal fossa (Forster, 1996): absent (0); present (1). In all chasmosaurines, a subcircular depression indents the centre of the premaxillary septum. This fossa is absent in all centrosaurines and outgroup taxa. (5) Premaxilla, caudal tip of posteroventral process inserts into an embayment in the nasal (Forster et al. 1993): present (0); absent (1). Primitively (e.g., Protoceratops), the tip of the posteroventral process of the premaxilla inserts into an embayment in the nasal and is thus surrounded by the nasal. This feature is retained in all species of Chasmosaurus, including C. irvinensis and Pentaceratops, although the morphology of the premaxilla is somewhat altered (see character 6). In all centrosaurines and other chasmosaurines, the distal end of the posteroventral process of the premaxilla lies entirely between the nasal and maxilla. (6) Premaxilla, posterior tip of posteroventral process forked (Forster et al. 1993): absent (0); present (1). In Protoceratops, centrosaurines, and some chasmosaurines, the distal posteroventral process of the premaxilla is a single process. In all species of Chasmosaurus, including C. irvinensis and Pentaceratops, this process is forked distally. The larger dorsal prong inserts into an embayment in the nasal, while the smaller ventral prong lies along the contact between the nasal and maxilla. (7) Nasal, horn core position (Forster 1990): centred posterior or posterodorsal to external naris (0); centred dorsal or anterodorsal to external naris (1). With the exception of Bagaceratops (Maryañska and Osmólska 1975), protoceratopsians lack nasal horns, although Protoceratops does exhibit a bilateral dorsal swelling of the nasals posterior to the external naris. Repreparation of the holotype of Montanoceratops shows conclusively that its purported nasal horn is actually a jugal. The nasal of Bagaceratops bears a low horn core well posterior to the external naris. Centrosaurines, Chasmosaurus belli, C. russelli, and C. mariscalensis all have posterior or posterodorsally placed nasal horns. In Pentaceratops, the nasal horn core has shifted forward to directly over the external naris. In C. irvinensis, the nasal horn of NMC 41357 is centred over the naris, while in TMP 87.45.1, the horn is posterodorsally placed. In one extremely large specimen of Pentaceratops, the nasal horn is centred over the anterior portion of the external naris (OMNH 10165, Lehman 1998). Among other chasmosaurines, the nasal horn core is posteriorly placed © 2001 NRC Canada

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in Anchiceratops, but shifted to the front of the external naris in all other taxa (e.g., Torosaurus, Triceratops). (8) Nasal, horn core length (Forster 1990): short, length of horn core less than 15% basal skull length (0); moderate to long, length of horn core 20% or more of basal skull length (1). All chasmosaurines, including C. irvinensis, have relatively short nasal horn cores. The nasal horn cores of centrosaurines are considerably longer, at least 20% of basal skull length. Character states are randomly assigned. (9) Postorbital, position of supraorbital ornamentation (Lehman 1996): centred anterodorsal or dorsal to orbit (0); centred posterodorsal or posterior to orbit (1). In Zuniceratops, Pentaceratops, and all species of Chasmosaurus, including C. irvinensis, the centre of the supraorbital horn core lies dorsal or anterodorsal to the orbit. In all other chasmosaurines, the centre of the horn core is positioned behind the middle of the orbit. The position of the supraorbital horn in centrosaurines is often difficult to ascertain due to their diminuitive size and the presence of resorption pitting (see character 12). However, when short supraorbital horns are present (e.g., Centrosaurus, AMNH 5239), they are centred over the middle of the orbit. Supraorbital horn cores are absent in Protoceratops. (10) Postorbital, length of supraorbital horn core in adults (Forster 1990): elongate, greater than 35% basal skull length (0); short, less than 15% basal skull length (1). Although all other protoceratopsians lack supraorbital horn cores, Zuniceratops possesses very elongate supraorbital horns (although no basal skull length is available for comparison). This supports the suggestion that long supraorbital horn cores are primitive for Ceratopsidae (Forster et al. 1993). Elongate horn cores also occur in nearly all chasmosaurines, with the exception of Chasmosaurus belli and C. russelli, which have both long and short morphs and are polymorphic for this character. The two known specimens of C. irvinensis preserving this part of the skull bear little more than low, rugose swellings over the orbits. While it is possible that C. irvinensis also has both long and short horn morphs, this is impossible to confirm based on currently known material. All centrosaurine taxa with supraorbital horn cores exhibit the short morph. (11) Postorbital, curvature of supraorbital horn core (Forster et al. 1993): posteriorly curved (0); anteriorly curved (1). The primitive condition, in which the axis of the supraorbital horn core curves posteriorly, is present in Zuniceratops, centrosaurines, Chasmosaurus belli (AMNH 5401), C. russelli (e.g., NMC 2280), and C. mariscalensis (e.g., TMM 43098-1). The condition cannot be coded for C. irvinensis, since its supraorbital horns are represented by pitted bosses (see character 12). In all other chasmosaurines, including Pentaceratops (e.g., AMNH 6325), the suporaorbital horn cores are curved anteriorly. (12) Postorbital, “resorption” pits replacing supraorbital horn cores: absent, well formed horn core present (0); present, horn core reduced to boss or absent (1). In Chasmosaurus belli, C. russelli, C. irvinensis, and all

centrosaurines with postorbital horns, an irregular pattern of pitting is often found invading either short, bosslike supraorbital horn cores or marking the place where the horn cores would be normally. Occassionally, these “resorption pits” occur unilaterally, paired with a short, well-formed horn core (e.g., Centrosaurus, NMC 348). This morphlogy is absent in C. mariscalensis, Pentaceratops, and other chasmosaurines that consistently possess well-formed supraorbital horns. (13) Jugal infratemporal flange (Brown and Schlaikjer 1940; Forster 1990): absent (0); present, contacts the jugal process of squamosal to form the ventral margin of lower temporal fenestra (1). Primitively, the jugal and squamosal do not contact below the lower temporal fenestra (e.g., Protoceratops). In centrosaurines, Chasmosaurus russelli and C. belli, a tablike process projects from the posterior margin of the jugal flange to contact the jugal process of the squamosal. Together they form the ventral margin of the lower temporal fenestra. In one specimen, most probably C. belli (UAVP 40), the jugal infratemporal flange is present but does not quite contact the squamosal (Godfrey and Holmes 1995). In C. irvinensis, (TMP 87.45.1), the jugal also contacts the squamosal below the infratemporal fenestra. The jugal infratemporal flange is absent in C. mariscalensis (e.g., TMM 430981) and all other chasmosaurines. (14) Supracranial cavity complex morphology (Forster 1990; Sampson 1995; Forster 1996): narrow and relatively shallow, does not underlie supraorbital ornamentation (0); broad and deep, underlies supraorbital ornamentation and may be confluent with cornual sinuses (1). Ceratopsids possess a system of supracranial cavities (dorsal to the braincase), the depth and extent of which varies among taxa. Centrosaurines, all species of Chasmosaurus including C. irvinensis, and some specimens of Pentaceratops (e.g., KUVP 16100) have narrow and shallow supracranial cavities and lack cornual sinuses. However, Lehman (1998) reported a cornual sinus in a large specimen of Pentaceratops (OMNH 10165), although the supracranial cavity in this specimen appears to remain relatively restricted. Other chasmosaurines (e.g., Triceratops, Torosaurus) have deep and extensive supracranial cavities that communicate with the cornual sinuses (Forster 1996). Deep and extensive cavities and cornual sinuses are also present in Anchiceratops (e.g., AMNH 5251). (15) Frontal fontanelle leading into a supracranial cavity complex: absent (0); present (1). A frontal fontanelle, the dorsal opening into the supracranial cavity complex, is present in all centrosaurines and chasmosaurines. Primitively, there is no supracranial cavity complex and thus no frontal fontanelle (e.g., Protoceratops). The condition is unknown in Zuniceratops. (16) Frontal fontanelle, shape in dorsal view (Forster 1996): transversely narrow, slit-like (0); keyhole shaped (1); oval to circular (2). The frontal fontanelle in all centrosaurines is an elongate, parallel-sided opening between the frontals. Frontal fontanelle shape varies within chasmosaurines. In all © 2001 NRC Canada

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species of Chasmosaurus, including C. irvinensis, and Pentaceratops, the frontal fontanelles are axially elongate but keyhole-shaped, being broader at their anterior end. All other chasmosaurines have broadly oval to circular frontal fontanelles. Rarely, specimens show irregular, surficial bridges of bone that span the opening in Chasmosaurus russelli (NMC 8800) and C. belli (YPM 2016). These bridges divide the fontanelle into anterior and posterior portions but do not affect the supracranial cavities. Character states are randomly assigned. (17) Parietosquamosal frill, maximum transverse width relative to interorbital skull width (Forster et al. 1993): greater than 2.5 times (0); less than 2.5 times (1). Protoceratops, Chasmosaurus belli (e.g., AMNH 5401), C. russelli (e.g., NMC 2280), and NMC 41357 are characterized by extremely broad, triangular frills that are at least 2.5 times the width of the interorbital roof. The condition of this character in C. mariscalensis cannot be determined on currently available materials. In other ceratopsids, the frills never exceed twice the width of the skull roof, except in the chasmosaurine Torosaurus latus (e.g., ANSP 15192). Since the wide frill is almost certainly a derived character for Torosaurus, other chasmosaurs are scored with the derived state. (18) Parietal, location of posteriormost portion: medial to lateralmost corner, more median position of posteriormost margin of the parietal (0); at lateralmost corner at junction with the squamosal (1). Primitively, the posterior margin of the parietal bows gently backward medial to the squamosal junction (e.g., Protoceratops, Leptoceratops). In Chasmosaurus belli and C. irvinensis, the posteriormost portion of the parietal is located at the parietalâ&#x20AC;&#x201C;squamosal juncton, with the parietal bowing at least slightly inward medially. In Chasmosaurus russelli, Pentaceratops, and all other chasmosaurines and centrosaurines, the posteriormost part of the parietal is located medial to the squamosalparietal junction. The condition is unknown in Chasmosaurus mariscalensis. (19) Parietal, length relative to squamosal: subequal in length (0); squamosal is noticably shorter than the parietal (1). In protoceratopsians (e.g., Protoceratops) and chasmosaurines, the squamosal is posteriorly elongated nearly to the same extent as the parietal. The derived condition, with a shortened squamosal relative to the parietal, is present in all centrosaurines.

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(20) Parietal, median embayment on posterior margin: absent or very slight indentation present (0); present, distinct moderate to large indentation present (1). Protoceratops and other protoceratopsians (e.g., Leptoceratops) have a slightly indented to gently convex posterior parietal margin. The posterior margin of the parietal shows a distinct median embayment in centrosaurines, Pentaceratops, Chasmosaurus russelli, C. mariscalensis, and rare specimens of C. belli. Most specimens of C. belli have virtually no embayment (e.g., NMC 2245). The parietal of C. irvinensis also lacks any embayment. In all other chasmosaurines, the posteror margin of the parietal is convex or straight, although occasional specimens of Triceratops have a very slight median embayment. Some centrosaur specimens appear

to have a deeply embayed parietal. However, most of this indentation is only apparent, caused by the anterior curl of the median parietal epoccipitals, and the posterior growth of the more lateral parietal epoccipitals. This is particularly apparent in juveniles that lack epoccipital development. (21) Parietal fenestra, maximum proximodistal diameter (adapted from Forster et al. 1993): occupies less than 40% of the total parietal length (0); occupies at least 45% or more of the total parietal length (1). The derived condition is restricted to Chasmosaurus belli, C. russelli, and Pentaceratops that have a relatively large parietal fenestra relative to parietal length. In these taxa, the parietal fenestrae extend over at least 45% total parietal length. In C. irvinensis, the parietal fenestrae are relatively smaller and more transversely oriented, occupying only 38% the length of the parietal. Protoceratops and all other ceratopsid taxa have relatively smaller parietal fenestrae, covering less than 40% total parietal length. The condition is unknown in C. mariscalensis, although fragments of the parietal (e.g., TMM P37.7.065) suggest that large parietal fenestrae were present in this taxon as well.

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(22) Parietal, posterior bar behind parietal fenestrae (Forster et al. 1993): relatively wide, 0.2 or more total parietal length (0); narrow and straplike, anteroposterior width 0.1 or less total parietal length (1). In all species of Chasmosaurus (e.g., YPM 2016), including C. irvinensis and Pentaceratops, the posterior margin of the parietal fenestra is relatively narrow and straplike. In Protoceratops, centrosaurines and all other chasmosaurines, the posterior border of the parietal fenestra is proportionally deeper anteroposteriorly. (23) Parietal, median bar, mediolateral width: relatively wide, 0.15 or more total parietal length (0); narrow and straplike, width less than 0.10 total parietal length (1). In Pentaceratops and all species of Chasmosaurus, the midline parietal bar, like the posterior bar, is extremely narrow, resulting in closely opposed parietal fenestrae. Despite the shortening of the parietal in Chasmosaurus irvinensis, its median bar remains relatively narrow and straplike. The parietal median bar is broad in Protoceratops, centrosaurines, and all other chasmosaurines. (24) Parietal, median bar, dorsoventral depth: dorsoventrally compressed, thin and straplike, (0); dorsoventrally deep, rectangular, square, or subcircular in cross section (1). In Chasmosaurus belli, C. russelli, and C. irvinensis, the midline bar is as deep or deeper dorsoventrally than wide, assuming a rectangular or subrectangular shape in cross section with flat lateral sides. The sides of the median bar facing the parietal fenestrae are often deeply incised with vasculature originating from the upper temporal fenestra (e.g., C. russelli, NMC 2280). The midline bar is dorsoventrally compressed and tapered laterally, in cross section forming an obtuse triangle in Protoceratops, C. mariscalensis, Pentaceratops, and all other ceratopsids. (25) Parietal, formation of the lateral margin of parietal fenestra: continuous around fenestra, parietal forms entire lateral margin of fenestra (0); may be discontinuous ÂŠ 2001 NRC Canada

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around fenestra, lateral margin completed by the squamosal (1). In Protoceratops and all other protoceratopsians, the parietal always forms the lateral margin of the parietal fenestrae. The parietal forms a discontinuous lateral margin of the parietal fenestra in some (but not all) specimens of Chasmosaurus belli, C. russelli, C. irvinensis, and Pentaceratops. Since no taxon shows the derived condition in all individuals, the polymorphic state is coded as derived in the interests of simplicity. The condition is unknown in C. mariscalensis. (26) Epoccipitals: absent (0); present (1). Epoccipitals, dermal ossifications ornamenting the margins of the parietal and squamosal, are present in all ceratopsids, but are absent in Protoceratops and all other protoceratopsians. The condition is unknown in Zuniceratops. (27) Epoccipitals, shape: crescentic or ellipsoidal (0); triangular (1). In centrosaurines, all unaltered epoccipitals are crescent-shaped or ellipsoidal with rounded apices and often slightly constricted bases. In all chasmosaurines, the epoccipitals are triangular with pointed apices, although the proportions vary greatly among taxa. The character state order is randomly assigned. (28) Epoccipitals on parietal, number per side: one to three (0); five or more (1). Nearly all Chasmosaurinae are characterized by the consistent presence of three parietal epoccipitals on each side. Additionally, Triceratops is apomorphic in having an extra epoccipital spanning the parietal midline. Specimens of Chasmosaurus belli have only a single, laterally placed

parietal epoccipital on each side and rugose regions more medially. Godfrey and Holmes (1995) suggested that each rugose region represents two modified epoccipitals. Although the parietal epoccipitals are similarly modified into irregular, rugose knobs in C. irvinensis, at least 5 individual ossifications per side can be discerned. All centrosaurines possess six or more parietal epoccipitals on each side. Character states are randomly assigned. (29) Epoccipitals, medial ossifications on parietal modified into procurved bony masses fused to each other at their bases: absent (0); present (1). In Chasmosaurus belli and C. irvinensis, the medialmost epoccipitals on the posterior parietal bar occur as gnarled, procurved masses that fuse at their bases to neighbouring epoccipitals. The precise extent of each element, therefore, can often only be estimated. This does not occur in any other ceratopsid. Character states are randomly assigned. (30) Epoccipitals on parietal, orientation relative to parietal margin at median loci: dorsally or anterodorsally directed (0); caudally directed (1). In several ceratopsid taxa, including some centrosaurines, Pentaceratops, Chasmosaurus belli, C. russelli, and C. irvinensis, the epoccipitals at the median locus or loci curl up and sometimes over the dorsum of the parietal. The condition is unknown in C. mariscalensis. In all other chasmosaurines, the median parietal epoccipitals are directly posteriorly, parallel to the frill surface. Character states are randomly assigned.

Appendix 2. Character Matrix

Table A1. Character Matrix. Characters

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Taxon Outgroup (Protoceratops and Zuniceratops) centrosaurines Chasmosaurus irvinensis Chasmosaurus belli Chasmosaurus russelli Chasmosaurus mariscalensis Pentaceratops sternbergi Other chasmosaurines Raw outgroup codings Protoceratops andrewsi Zuniceratops christopheri

12345

67891

11111

11112

22222

22223

00?00 00?01 11010 11010 11010 11010 11110 10?11

0 00000 0010/11 10/1001 10000/1 10000/1 10000 11000 00/1010

12345 000?0 01101 ?1101 01101 01101 00001 1000/11 10011

67890 ?0000 01010 10100 10100/1 10001 1??01 11001 21000

12345 00000 00000 01111 11111 11111 ?110? 11101 00000

67890 0???? 10100/1 11110 11010 11000 11??? 11000 11001

00?00 ?????

000?? ???00

??0?0 00???

?0000 ???0?

00000 ?????

0???? ?????

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