Kirkland J. I., and DeBlieux, D. D. 2010 New basal centrosaurine ceratopsian skulls from the Wahweap Formation (Middle Campanian), Grand Staircase– Escalante National Monument, southern Utah ; in Ryan, M.J., Chinnery-Allgeier, B.J., and Eberth, D.A. (eds.) New Perspectives on Horned Dinosaurs: The Royal Tyrell Museum Ceratopsian Symposium, Bloomington, Indiana University Press, p. 117 – 140. more

NEW BASAL CENTROSAURINE CERATOPSIAN SKULLS FROM THE WAHWEAP FORMATION (MIDDLE CAMPANIAN), GRAND STAIRCASE – ESCALANTE NATIONAL MONUMENT, SOUTHERN UTAH JAMES I. KIRKLAND and DONALD D. DE BLIEUX, Utah Geological Survey, P.O. Box 146100, Salt Lake City, UT 84114-6100 RH: KIRKLAND AND DE BLIEUX—NEW WAHWEAP CENTROSAURINES preprint Kirkland J. I., and DeBlieux, D. D. 2010 New basal centrosaurine ceratopsian skulls from the Wahweap Formation (Middle Campanian), Grand Staircase– Escalante National Monument, southern Utah ; in Ryan, M.J., Chinnery-Allgeier, B.J., and Eberth, D.A. (eds.) New Perspectives on Horned Dinosaurs: The Royal Tyrell Museum Ceratopsian Symposium, Bloomington, Indiana University Press, p. 117 – 140. 1 ABSTRACT A new basal centrosaurine ceratopsid, Diabloceratops eatoni, is described from the Wahweap Formation (lower to middle Campanian, Upper Cretaceous) of Grand Staircase-Escalante National Monument, southern Utah. The isolated, nearly complete skull is one of the oldest and is the first diagnosable centrosaurine recovered south of Montana. It shares with more derived centrosaurines a stepped squamosal and a nasalpremaxillary process along the caudal border of the naris. The species may be diagnosed by numerous autapomorphies relative to other centrosaurines: 1) the preorbital skull is deeper and shorter than other known ceratopsids, 2) rostral to a low, subconical nasal horn is a smaller "epinasal", 3) a large accessory antorbital fenestra is present, 4) fused frontals form a steep vault between large postorbital horns at level of palpebrals, 5) elongate jugals expose the caudal end of maxillae in lateral view, 6) large, triangular, vertically oriented, blade-like epijugal extends laterally from the jugal bone, 7) the erect frill is widest at the laterally directed squamosals, tapering to half its width at the base of a pair of elongate caudal parietal spines separated by a medial notch, 8) epoccipitals on the lateral margin of parietal decrease in size caudally to base of parietal spines, and 9) the parietal fenestrae are caudorostrally elongate. The long postorbital horns and small narial horn are primitive character states for ceratopsids as indicated by the ceratopsid sister taxon Zuniceratops. The basal position of Diabloceratops among centrosaurines is supported by the ascending process of the premaxilla not contacting the lacrimal as in 2 other centrosaurines; rather it terminates rostrally to this element as in Zuniceratops and all chasmosaurines. A second, larger partial centrosaurine skull recovered from the Wahweap Formation is not represented by enough critical elements to be confidently diagnosed. We tentatively placed it in the genus Diabloceratops based on the presence of long postorbital horns, and a dorsoventrally oriented attachment scar on the jugal bone, indicating the presence of a possibly similar blade-like epijugal. It can be distinguished from Diabloceratops eatoni in bearing epoccipitals closely appressed to either side of the squamosal-parietal suture. The presence of a well-developed accessory antorbital fenestra in Diabloceratops is shared with its sister taxon Zuniceratops. Among more basal neoceratopsians, only Magnirostris and Bagaceratops share this distinct character. The presence of distinct, albeit tiny, postorbital horns, indicates that Magnirostris is the Asian sister taxon to North America’s larger ceratopsids. INTRODUCTION The study of microvertebrate fossils collected via wet screen-washing by researchers from the Museum of Northern Arizona, University of Oklahoma, and Weber State University has documented that the Wahweap Formation on the Kaiparowits Plateau of southern Utah preserves the most diverse lower-middle Campanian terrestrial fauna in North America (Fig. 1). These studies have documented four freshwater shark species, two freshwater ray species, seven bony fish species, two amphibian species, six turtle genera, two lizard taxa, three crocodilian taxa, eight dinosaur taxa, and 23 mammal species (Eaton et al., 1999). With the establishment of the Grand Staircase – Escalante 3 National Monument (GSENM) by President Bill Clinton in 1996, the Kaiparowits Plateau was incorporated into the largest national monument in the lower 48 states. Subsequently, the U.S. Bureau of Land Management (BLM) funded the Utah Geological Survey (UGS) to refine the locality data for known paleontological sites and begin efforts to document additional paleontological resources (Foster et al., 2001). In 2001, we began the Wahweap Project, aimed at inventorying fossil localities in the lower sandstone and middle mudstone members of the Wahweap Formation across the southern end of the Kaiparowits Basin (Plateau) to serve as a management tool for the BLM. In addition to providing data on the distribution of paleontological resources, this study has identified and recovered specimens that are adding to our knowledge of terrestrial faunas during a time interval for which they are poorly known. To date, there are still only two dinosaurs had been identified to species from rocks of this approximate age in North America (lower Two Medicine Formation of Montana), a hadrosaurine hadrosaurid Gryposaurus latidens (Horner, 1992) and a “protoceratopsian” grade basal ceratopsian Cerasinops hodgkissi (Chinnery and Horner, 2007). As discussed below, these dinosaurs are now thought to be a couple of million years older than the Wahweap Formation. A number of associated hadrosaurid skeletons have been identified in the field, although taxonomically critical cranial remains have yet to be identified in these asyet preliminary excavations. The isolated skull roof of a juvenile pachycephalosaur has also been collected. Additionally, carnivorous dinosaur remains have been identified at a number of sites, but nothing diagnostic has yet come to light (Kirkland and DeBlieux, 2005). At GSENM, cranial remains of long-horned centrosaurine ceratopsids are the most significant dinosaur fossils to be identified so far from the Wahweap Formation. 4 Joshua A. Smith, while working for the UGS, discovered a skull of a ceratopsid dinosaur during a July 16, 1998, UGS paleontological survey of GSENM, in the lower Wahweap Formation at the top of the lower sandstone member on the south end of the Kaiparowits Plateau, northwest of Nipple Butte. The Nipple Butte skull is the first ceratopsid specimen identified from the Wahweap Formation. Although the skull had been exposed on the surface for many years and had broken into three major sections, it was obviously an important specimen that required salvage. The skull was collected in August 2000 by the UGS, aided by the University of Utah and Utah Friends of Paleontology (Fig. 2). The skull was found one-third of a mile off an established dirt road, and, because wheeled vehicles are not permitted off-road, the three large sandstone blocks were dragged out by an eight-person team using the roof of an old Ford Mustang as a sled (Kirkland, 2001). Following hundreds of hours of preparation, the Nipple Butte skull was identified as a centrosaurine ceratopsid dinosaur (Stokstad, 2001; Kirkland et al., 2002). However, lacking the nasal area and the rear of the frill, we concluded that given the recent discovery of other centrosaurines with large postorbital horns (Ryan, 2003, 2007a), the specimen is not fully diagnostic as to genus. In 2002, Don DeBlieux discovered a skull weathering out of a sandstone ledge near the middle of the middle mudstone member of the Wahweap Formation (Eaton, 1991) near Last Chance Creek on the north side of Reynolds Point in the eastern Wahweap outcrop belt (Fig. 3). The collection of bone on the surface and cleaning of the block revealed a nearly complete skull lying on its left side; part of the right side had eroded away, with much of the skull still imbedded in the rock (Fig. 3). We spent eight days using a gas-powered cutoff saw to separate the block containing the skull from the 5 surrounding ledge. In September 2005, arrangements were finalized by the BLM to airlift the block containing the skull out of the backcountry (Fig. 3). The block was then transported by helicopter to a truck waiting on a nearby road and driven to the UGS preparation lab in Salt Lake City, Utah. More than 800 hours of preparation (by D. D.) were needed to expose the beautifully preserved skull. The Last Chance skull is the first diagnosable, centrosaurine ceratopsid dinosaur older than Late Campanian, and the first diagnosable, centrosaurine ceratopsid dinosaur recovered south of Montana. Herein, we describe and diagnose the Last Chance skull as a new basal centrosaurine ceratopsid dinosaur and contrast it with the Nipple Butte skull, and other pertinent neoceratopsian skulls. Both skulls are curated into the vertebrate paleontology collections of the Utah Museum of Natural History at the University of Utah in Salt Lake City, Utah. Institutional Abbreviations AMNH, American Museum of Natural History, New York; CMN, Canadian Museum of Nature (National Museum of Canada), Ottawa; DMNH, Denver Museum of Natural History and Science, Denver, IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing; NMMNHS, New Mexico Museum of Natural History and Science, Albuquerque; TMM, Texas Memorial Museum, Austin, Texas; TMP, Royal Tyrrell Museum of Paleontology, Drumheller; UMNH, Utah Museum of Natural History, Salt Lake City. 6 SYSTEMATIC PALEONTOLOGY ORNITHISCHIA Seeley, 1888 CERATOPSIA Marsh, 1990 NEOCERATOPSIA Sereno, 1986 CERATOPSIDAE Marsh, 1888 CENTROSAURINAE Lambe, 1915 DIABLOCERATOPS EATONI gen. et sp. nov. Holotype— The "Last Chance" skull, UMNH VP 16699, a skull preserving the entire left side of the skull and portions of the right side. UMNH VP 16699 preserves the entire left side of the skull including the midline (Fig. 4, 5). The skull was sagitally sectioned by erosion through the right side, resulting in the loss of the right squamosal, half of the right postorbital horn, jugal, and part of the maxilla. A number of fragments from the right side were recovered. A rib had come to rest between the two horns lying against the left side of the face. A partial splenial bone was also found adjacent to the skull during excavation. The bone of the skull is very well preserved and almost completely undistorted. Sutures are well fused but can be distinguished in most cases, and the epoccipitals on the squamosal and parietal are well fused, indicating that this specimen is adult. Type Locality—42Ka800V Grand Staircase-Escalante National Monument on the south side of Last Chance Canyon on the north flank of Reynolds Point west of Smoky Mountain Road, central Kaiparowits Plateau, Utah. 7 Stratigraphic Occurrence—The skull was found in a medium-grained, trough cross-bedded, sandstone ledge with common clay clasts and bone fragments, including turtle shell fragments and isolated teeth, in the Wahweap Formation at 105.30 m above contact with underlying Drip Tank Member of Straight Cliffs Formation near middle of middle mudstone member, 51.72 m above its base. Diagnosis— A relatively small centrosaurine ceratopsid (skull estimated at 62 cm from rostrum to condyle) with a large accessory antorbital opening bounded by the premaxilla, maxilla, and nasal, such that the premaxilla is excluded from contact with lacrimal by maxilla; preorbital skull is deep and shorter than other known centrosaurines; small epinasal rostral to low narial horn; large postorbital horns extending rostrally to narial horn; elongate jugal exposes caudal end of maxilla in lateral view; vertically oriented, blade-like epijugals larger than in other described centrosaurines; fused frontals form steep vault between orbital horns rostral to palpebrals; erect frill is subequal in length to skull, widest at laterally directed squamosals, tapering by 50% to a pair of elongate caudal parietal spines separated by a midline notch; laterally parietal epoccipitals decrease in size caudally; parietal fenestrae are triangular and caudorostrally elongate. Etymology— "Diablo," Spanish for devil in reference to the pair of long sweeping spines on the back of the frill; + "ceratops," horned-face, Latinized Greek. "eatoni"— A patronym in honor of Jeffery G. Eaton, a paleontologist at Weber State University in Ogden, Utah, in recognition for his extensive work on the Cretaceous vertebrate faunas of southern Utah, and his role in the establishment of Grand StaircaseEscalante National Monument. 8 DESCRIPTION The skull is ~1 m long from the beak to the back of the frill, where a pair of curved spines adds another 0.5 m to the total length. The base length of skull is estimated at 62 cm (rostrum to condyle), and the occipital condyle is 54.4 mm in diameter. The skull shares with more derived centrosaurines a stepped squamosal and a nasalpremaxillary process along the caudal border of the naris (Fig. 4). The preorbital skull is deep and shorter than other known centrosaurines. Snout Most of the rostral has been lost to erosion with much of the right side extracted as a cast of the external sandstone mold using epoxy putty. The ventral portion is preserved on the left side; the rugosity of the rostral and the suture with the premaxilla are typical of other ceratopsids. Both the premaxillae are preserved. The tall premaxillae contribute to a deep muzzle in Diabloceratops. The sutured dorsal and anterior margin is rugose delineating the anterior extent of the soft narial tissue. The narrow, blade-like premaxillae are similar to those found in other centrosaurines (Fig. 4, 5). The rostral portion is deep and forms a simple smooth nasal septum that bears one small nutrient foramen, entering ventrally, along its anterior edge adjacent the rostral bone. There is no secondary opening, fossa, or narial strut as in chasmosaurines (Lehman, 1993; Dodson et al., 2004). At the caudal border of the external naris, the ascending process of the premaxilla, along with the rostroventral border of the nasal, forms a small process as in other centrosaurines (Dodson et al., 2004; Ryan, 2007a). The caudal portion of the ascending process of the 9 premaxilla overlaps the nasal and forks to form the rostral and ventral border of an accessory antorbital fenestra. Unlike the condition in other centrosaurines, the ascending process of the premaxilla does not contact the lacrimal; rather, it terminates well rostral to this element as in chasmosaurines. Ventral to the naries, the ventral margin of the premaxillae has a narrow, ventral expansion (offset just medial to the lateral margin) as in other centrosaurines (Ryan, 2007b). In centrosaurines that preserve this region, this ventral expansion matches a trough in the caudal ramae of the predentary, where it onlaps the dentary, forming a crushing surface. Although present in UMNH VP 16699, this expansion is modest compared to the condition seen in other centrosaurines. The paired nasal bones are completely fused along the midline and bear a long (ovate base), low, robust, subconical narial horn. This horn lies dorsal to the caudal-most edge of the nasal opening. Rostral to this is a smaller ossification, or epinasal, that may have borne a second horn. The epinasal is more coarsely textured than the nasal horn and is located dorsal to the anterior portion of the nasal opening, extending rostrally to the suture with the premaxilla. The rostral contact of the nasal and premaxilla is similar to that seen in other centrosaurines. The caudal half of the dorsal margin of the accessory antorbital fenestra is formed by the nasal. The sutures of the nasal with the maxilla and the lacrimal are discernable along the dorsal margin of the antorbital fossa. Sutures along the contact of the nasal with the frontal and the palpebral are completely fused and difficult to identify (Fig. 4). The triangular maxilla is preserved on the left side, whereas only an impression of the interior of the maxilla is preserved on the right side. The maxilla is of typical ceratopsid morphology. Caudal to the ascending process of the maxilla, the maxilla 10 contacts the lacrimal. The contact with the nasal and lacrimal forms the dorsal margin of an antorbital fossa. The antorbital fenestra, as is typical for ceratopsids, is small and lies in a crescent shaped trough, the caudal margin of which lies between the maxillary contact with the lacrimal and the jugal. The antorbital fenestra forms the caudoventral margin of the antorbital fossa, which extends rostrally across the ascending process of the maxilla to the accessory antorbital fenestra (Fig. 6). The ascending process of the maxilla contacts the premaxilla rostroventrally, forms the caudoventral border of the accessory antorbital fenestra, and contacts the nasal along its triangular dorsal apex. A well-defined suture is visible between the maxilla and the jugal and exhibits typical ceratopsid morphology. The ventral portion of the palatine contacts the medial surface of the maxilla, and the ectopterygoid extends along the dorsal surface of the maxilla caudal to its ascending process. The pterygoids extend across medial-dorsal margin of the ectopterygoids, twisting laterally, to contact the most caudal dorsolateral surface of maxilla obscuring the most posterior tooth in lateral view. Diabloceratops eatoni is unique in having the caudal end of the maxilla visible rostral to epijugals in lateral view (Fig. 4). The maxilla contains 24 tooth rows preserving teeth in various stages of wear and replacement. The continuous wear surface is nearly vertical as in other ceratopsids. Although not visible, we predict that the teeth are double rooted. There are several dorsocaudally directed nutrient foramina entering the maxilla above the tooth row along rostral half of the maxilla. Circumorbital region and skull roof 11 The orbit in Diabloceratops is formed by the jugal, lacrimal, palpebral, and postorbital. The most significant features of this region are the long, erect, postorbital horns (25 cm long from top of the orbits) a feature seen primarily in chasmosaurines and shared only with Albertaceratops among described centrosaurines (Ryan, 2007a). The entire left postorbital horn is preserved, whereas only the medial half of the right horn is well preserved, although fragments of the lateral portion of the horn were recovered (Fig. 4, 5). The postorbital horns are inclined rostrally to a point just caudal to the low narial horn and are gently curved dorsally. The surface texture of the postorbital horns is characterized by shallow, longitudinal grooves, a feature seen in Albertaceratops and many of the long-horned chasmosaurines (Ryan, 2007a). The bases of the horns are robust and subtriangular in cross-section, being flattened laterally. The cross-section of the right horn demonstrates that there is no sinus in the base of the postorbital horns. The bases of the postorbital horns along with the skull roof bones form a tall, steep vault nearly as deep as the palpebrals forming a "forehead" that is relatively larger than that of any other ceratopsid. Ryan (2007a) noted a similar feature, massive "vaulted frontals,” in Albertaceratops (WDCB-MC-001). Complete fusion of the frontals and prefrontals has obscured all sutures on the skull roof. Robust, blocky, strongly grooved palpebrals form a buttress along the rostrodorsal margins of the orbits in continuity with the postorbital horns and form the lateral margins of the “forehead.” Ventral to this buttress, the lacrimals are flush with the lateral surface of the skull and form a smooth rim along the rostroventral margin of the orbits. The orbits are oval with the long axis of the oval oriented rostrodorsally in line with the postorbital horn. 12 On the skull roof caudal to the postorbital horns, the well-developed frontal fontanelle forms an elongate oval with straight sides (Fig. 7) as in other centrosaurines (Dodson, et al., 2004). Although the frontal fontanelle displays a range of interesting morphologies in centrosaurines, this feature has not yet been shown to be of taxonomic importance within the group (Sampson, et al., 1997). Temporal region The jugal is preserved on only the left side of the skull. The sutures delineating the contacts of the jugal bone with surrounding elements are well defined and are typical of ceratopsids. The jugal is more caudorostrally elongate than in other Neoceratopsia. In line with the ascending process of the left maxilla, its ventral margin is gently arched dorsally and laterally. The most prominent feature of the jugal is the vertically oriented, subtriangular, blade-shaped, epijugal. This epijugal is relatively larger than in any other ceratopsid that we have examined and much larger than in any known centrosaurine. Large epijugals are more commonly found in the chasmosaurines. The epijugal was highly vascularized as shown by the numerous blood vessel grooves on the epijugal. The large, wedge-shaped quadratojugal separates the jugal from the quadrate medially and supports the caudal margin of the epijugals. The exterior surface of the jugal is characterized by a number of depressions or shallow dimples, about 1-1.5 cm across, that may have resulted from an interaction with the integument. The jugal forms the rostral half of the dorsal margin of the circular infratemporal fenestra, which is 54 mm wide and 64 mm tall. A triangular process of the jugal bone forms the ventral border of the infratemporal fenestra. The quadrate process of the squamosal makes up the posterior margin of the fenestra. The contact between the jugal and squamosal overlying the 13 infratemporal fenestra is obscured by a presumed pathology taking the form of a circular opening 33 mm in diameter in the rostral portion of the squamosal. This opening overlies and is connected to the infratemporal fenestra at the position of this suture. The contacts between the jugal, quadratojugal, and quadrate are well defined and similar to those of other ceratopsids. The squamosal bone is discussed below with the frill. Palatal region The left quadrate is well preserved and is much like that of other centrosaurines. Its dorsal contact with the squamosal is obscured rostrally behind the paraoccipital process of the braincase (Fig. 8). The main body of the quadrate is straight and rostrocaudally flattened with a slight depression extending down its length ventrally. There is an extensive medial (pterygoid) flange that is overlain caudally by the pterygoid. Ventral to a moderate constriction in the quadrate shaft, its lateral and medial condyles are 75 mm across and form a roughened surface that was the substrate for the cartilaginous articulation for the lower jaw. The medial condyle is 33 mm across rostrocaudally and the lateral condyle is slightly lower and more rostral, measuring 41 mm across rostrocaudally (Fig. 8). The left pterygoid is completely preserved but has not been fully exposed by preparation. The extensive quadrate wings expand laterally and are broadly forked where they overlap the pterygoid flange. Just rostral to the articulation with the pterygoid process of the basisphenoid, a dorsomedially directed fold is formed that corresponds to the “eustachial” canal (Fig. 9) described in Triceratops (Hatcher et al., 1907). Samson (1997) noted that in centrosaurines this feature is typically represented by a shallow trough. 14 The complete left palatine is preserved, but portions of it are still obscured by matrix. Its contacts with the caudodorsal margin of the maxilla, medially, and the pterygoid, caudally, are well expressed. Medially, it forms the rostral margin of the ventral notch that is formed caudal to the maxilla between it and the quadrate. The dorsal margin of the right palatine is preserved, where it overlaps the rostrolateral wall of the braincase. As discussed above, the ectopterygoid is a narrow element overlapping the caudodorsal surface of the maxilla, lateral to the palatines. It is marked by an elongate, rugose tuberosity on its exposed dorsal surface as in other centrosaurines (Sampson, 1993). Braincase As with all adult ceratopsian braincases, the sutures of nearly every element are completely fused. The right side of the braincase was removed by erosion prior to discovery, such that most of the right paraoccipital process and basitubera are missing and the entire right side of braincase and the cranial nerve openings are well exposed. Thus, all elements of the braincase are well represented and the braincase is highly informative. The supraoccitpial region of the parietal surrounding the dorsal side of braincase bears a number of recesses or fossae for the attachment of nuccal musculature. The supraoccipital forms a long keel above the foramen magnum separating two of these fossae. Near its dorsal end is pair of small tabs of bone that extend caudally. It is well fused with the parietal dorsally, which has a deep medial fossa caudal to this contact on 15 the rostroventral surface of the parietal at the base of the parietal bar. The ventral end of the supraoccipital preserves its suture with the underlying exoccipitals. The paraoccipital processes are made up of the fused exoccipitals and opisthotics. They extend laterally, expanding dorsoventrally to fit in a groove formed on the medial surface of the squamosal posterior to articulation with the quadrate. The ventral margin of the paraoccipital extends ventrally below the base of the flange of the squamosal such that the base of the paraoccipital process is exposed below the quadrate process of squamosal in lateral view. Although possibly pathologic in UMNH VP 16699, as discussed below, this unusual condition is symmetrically developed in Centrosaurus “nasacornis” (AMNH 5351). The foramen magnum is oval to subrectangular (18 mm wide and 34 mm tall). The exoccipitals completely enclose the foramen magnum and form a thin shelf that extends caudally from the base of the supraoccipital to extend over the foramen magnum. A fossa in the base of the exoccipitals, at the base of the paroccipital processes on either side of the foramen magnum, has three openings for cranial nerves IX-XII. The spherical occipital condyle is fully fused on a short neck that is ventrally inclined. The basioccipital makes up the lower one third of the condyle and is completely fused with the basisphenoid rostrally. At its contact with the basisphenoid, the basioccipital supports a pair of massive, basal tuberosities of which only the left is completely preserved. The basal tuberosities are highly rugose and flare ventrally and laterally from the base of the braincase. Anterior to the basituberae the basisphenoid supports a pair of robust pterygoid processes that angle rostrocaudally away from the 16 braincase to buttress the pterygoids. A trough between the basal tuberosities and the pterygoid processes marks the route of the carotid artery. The lateral wall of the braincase is exposed on the incomplete right side of the skull. The laterosphenoid and prootic are completely fused with each other and the surrounding bones of the braincase. A robust laterosphenoid buttress extends rostrodorsally along the wall of the braincase to join the postorbital below the base of the horn and separates the medal surface of the supratemporal from a rostral fossa. The dorsal side of the rostral fossa is partially crushed into the frontal sinus below the horn. The openings for cranial nerves IV, II, III, and VI extend in a line ventrally just rostral to the laterosphenoid buttress (Fig. 9.). Extending caudally to the base of the paraoccipital process and ventral to the laterosphenoid buttress, the area of the prootic is a shallow fossa with the openings for the trigeminal nerves (V2-V3 and V1) caudal to the opening for VI and rostral to the opening for VII. The auditory nerve (VIII) passes through the foramen ovale posterior to the opening for the facial nerve (VII). Frill In Diabloceratops, the parietal and squamosal bones form the frill as in all other ceratopsids. The entire left side of the frill, including most of the midline parietal bar, is preserved in UMNH VP 16699 (Fig. 3, 4). The erect frill is subequal in length to the skull and is widest at the laterally directed squamosals, tapering to about half its width at the base of a pair of caudal parietal spines separated by a midline notch. This gives the frill of Diabloceratops a caudally tapered appearance, which is unique among the Centrosaurinae. 17 The squamosal is short and square and forms the rostroventral margin of the frill. The narrow squamosal bears two large epoccipitals laterally and possibly two weak epoccipitals rostrally (Kirkland and DeBlieux, 2007). The caudal contact between the squamosal and parietal bears the "stepped" condition that defines the Centrosaurinae (Dodson et al., 2004). The squamosal/parietal suture at the lateral margin of frill is separated rostrocaudally by about 1 cm. A gap in the series of epoccipitals along the lateral frill margin, spanning this suture between the squamosal and parietal, may have borne an epoccipital spaning this suture that had been lost. The morphology of the squamosal in the region caudal to the quadrate, the alleged jugal notch, is distinctive in UMNH VP 16699. In ceratopsids, the squamosal expands laterally such that there is a notch between the back of the skull (quadrate) and the frill that housed the external ear. In type of Diabloceratops eatoni, Zuniceratops, and more basal neoceratopsids, the notch is not developed such that the posterior surface of the quadrate and the ventral surface of the squamosal make a right or obtuse angle. However, it was pointed out to us by Andrew Farke (2007, personal commun.) that the ventral margin of this squamosal maybe pathologic. Close examination of this surface does not reveal obvious signs of pathology showing that, if present, the pathology was well healed. It is possible, though, that the straight ventral margin and two weakly developed epoccipitals on the ventral margin may actually be artifacts of a healed pathology. As the right squamosal is not preserved it is impossible to test the symmetry of this feature in UMNH VP 16699. Another interesting feature is a circular opening dorsal to the infratemporal fenestra at the suture between the squamosal and the jugal on the rostral part of the left squamosal. This feature is likely pathological, possibly the result of intraspecific conflict 18 (Sampson, 1997). However, a recent study by Tanke and Farke (2007) has shown that healed traumatic injuries are quite rare in ceratopsids, and lesions and fenestrae not attributable to trauma are found on many centrosaurine squamosals. Lacking a right squamosal, we cannot be certain that this opening is pathological, but we think it is unlikely that this feature would have been present on the other side. The broad parietal bar is broadly convex dorsally and preserves barely discernable undulations on its dorsal surface, but it has no distinct ornamentation. It is ventrally concave in cross-section unlike other centrosaurines. There is a small (~1 cm) triangular process that projects laterally into the parietal fenestra near its widest point, 5 cm from the rostral margin of the parietal fenestra (Fig. 4). This feature may to be related to the connective tissues spanning across the parietal fenestra. Rostrally, the parietal bar overlaps the caudal margin of the frontal fontanelle, where it divides into three rounded prongs as in other centrosaurines (Fig. 7). The lateral margins of the frontal fontanelle are formed by smooth, depressed rostral projections of the parietal forming sulcae connecting the fontanelle with the supratemporal openings on either side. Penkalski and Dodson (1999) report that this character is variable even within species, but it appears to be widespread in centrosaurines (pers. observ.; Farke, 2006). Laterally, the parietal is thin and bears five triangular epoccipitals (Fig. 4), which are slightly flexed dorsally, with the largest near its suture with the squamosal. The epoccipitals are progressively smaller caudally such that the epoccipital at the base of the caudal parietal spine is less than one square centimeter in size. Numerous vascular grooves are appressed into the lateral parietal; they are especially prominent on the 19 ventral surface where they form a branching network. Two robust spines dominate the caudal parietal margin and are nearly as long as the entire frill. These spines extend caudally and then gradually sweep laterally beyond the widest portion of frill. Using the classification marginal processes devised by Sampson et al. (1997), this large spine would correspond to process 3 and be homologous to the large parietal spines seen at this locus in Styracosaurus, Einiosaurus, and Achelosaurus, among others. There is no indication of any processes medial to the large spines (parietal loci 1 and 2) in Diabloceratops. The parietal fenestra is elongate (315 mm long and ~170 mm wide rostrally) and, due to the narrowing of the frill caudally, triangular, in contrast with the oval parietal fenestrae seen in most centrosaurines. A raised rugose area extends laterally from the parietal bar just rostral to the parietal fenestra and would have defined the caudal limit of the jaw adductor muscles on the parietal, excluding them completely from the area of the parietal fenestra. The surface texture of the preserved left parietal spine is mottled and marked by a series of longitudinal vascular grooves. There is a well-defined collar caudal to the base of the caudal spine where the surface texture changes from smooth to mottled. Several distinct sections can be identified in the caudal spine that suggest it grew as a series of stacked conical ossifications. cf. DIABLOCERATOPS sp. Material— The "Nipple Butte" skull (UMNH VP 16704), discovered by Joshua A. Smith in 1998 near the top of the lower sandstone member of the Wahweap Formation (Eaton, 1991) on the south side of the Wahweap outcrop belt. Collected in 2000, the skull 20 was eroded into three large blocks (Fig. 2) and numerous fragments; it preserves part of the right side of the frill, occipital condyle, posterior braincase, portions of the right pterygoid and maxilla, right jugal, a portion of the right orbital and antorbital region (lacrimal and palpebral), palate, left maxilla, and pterygoid, a partial postorbital horn core. Locality—42K586V Grand Staircase-Escalante National Monument, on the top of a low ridge on north side of Nipple Butte southwestern Kaiparowits Plateau, Utah. Stratigraphic Occurrence—The skull was found in a medium-grained, slabby, cross-bedded, sandstone ledge with common clay clasts and bone fragments, including turtle shell fragments (one partial turtle) and isolated teeth that were found at the base of the ledge a few meters laterally to the north of the skull. Found in the Wahweap Formation in the uppermost sandstone of the lower sandstone member about 50 m above contact with underlying Drip Tank Member of Straight Cliffs Formation. Description— The description UMNH VP 16704 is arranged as description of elements preserved in each major sandstone block. The largest block, Block 1, preserves a portion of the right frill including the distal portion of the postorbital, a portion of the jugal, the paraoccipital process of the exoccipital, most of the squamosal, and the rostral portion of the medial and lateral parietal. Also preserved are the braincase, the left pterygoid, and portions of both the right and left maxillae and possibly the left palatine. The right frill fragment in UMNH VP 16704 preserves a large distally flaring squamosal with a stepped squamosal-parietal suture; preserved elements are larger than the corresponding elements in UMNH VP 16699 (Fig. 10). Two low epoccipitals are 21 present along the lateral margin of the squamosal. A portion of the lateral parietal displays two long and low epoccipitals (Fig. 10). There is an even larger rostrodorsal displacement of the parietal/squamosal suture on the lateral margin of the frill, than is observed in UMNH VP 16699, but unlike the type specimen of Diabloceratops eatoni, the epoccipitals on either side of this suture are closely spaced and there would be no space for an epoccipital spanning the suture. The dorsal surface of the squamosal and parietal have a rugose surface texture characterized by many pits and grooves; larger vascular channels are also present (Fig. 10). The rostral portion of the parietal fenestra is 234 mm wide with a fairly straight margin. The preserved anterior margin of the parietal fenestra is slightly more oval than the parietal fenestra in UMNH VP 16699. The basicranium preserves the occipital condyle (57.8 mm in diameter), both basituberae, and basipterygoid processes, the ventral margin of the maxilla, and much of the left pterygoid bone (Fig. 11). This region is large than the corresponding region in UMNH VP 16699. The pterygoid is particularly well preserved with the medial side preserving a well-developed fold corresponding to the “eustachial” canal described in Triceratops by Hatcher et al. (1907; see also Penkalski and Dodson, 1999). The dorsal portion of the braincase, including the foramen magnum, is damaged and poorly preserved. Much of the bone in Block 2 has been lost to erosion leaving primarily bone impressions. Part of the left orbital region is preserved including what may be the base of a postorbital horn. There is also an internal mold that may be from the nasal region caudal to the external nares. 22 Block 3 preserves much of the right jugal, a portion of the right maxilla (ascending ramus and rostomedial portion), and the rostromedial portion of the left maxilla (Fig. 12). The external surface of the jugal has a rugose texture and does not display the dimpled features seen on UMNH VP 16699. The rostromedial portion of the maxillae extends to the midline forming a slightly arching partial palate. The ascending process of the right maxilla and right jugal form a broad arch as in the type of Diabloceratops. The caudal jugal has a large articular facet that compares favorably with the morphology of the articulation of the large epijugal in the type of Diabloceratops, an indication that it may have possessed a large, vertically-oriented epijugal. Initially, when only partially prepared, the presence of a large epijugal was not recognized (Kirkland and DeBlieux, 2007). The ventral and rostral portion of the right orbit is preserved and is similar to that seen in UMNH VP 16699, though with a dorsorostral margin (palpebral) that is triangular in cross-section and less rectangular than in UMNH VP 16699. The antorbital fenestra is preserved, and the trough housing it is shorter than that in the type of Diabloceratops but generally similar in morphology. The presence or absence of an accessory antorbital fenestra cannot be determined because of the loss of this area to erosion. It appears that UMNH VP 16704 may have had the vaulted supraorbital "forehead" seen in UMNH VP 16699. DISCUSSION Age The age of the contact of the Wahweap Formation with the underlying Drip Tank Member of the Straight Cliffs Formation is Early Campanian, based on the occurrence of 23 the latest Santonian ammonite Desmoscaphites in the upper marine tongue of the John Henry Member that underlies the Drip Tank (Peterson, 1969; Eaton, 1991). A maximum detrital zircon date of 84 Ma from the basal Wahweap Formation (Link et al., 2007) probably represents reworked Upper Santonian (Ogg et al., 2004) strata from the upper John Henry Member of the Straight Cliffs Formation. Jinnah et al. (2007) published an 40AR/39AR date of 80.1 ± 0.3 from an ash near the base of the middle mudstone member of the Wahweap Formation, 54 m above the base of the formation. This is nearly the same stratigraphic level of the Nipple Butte skull and indicates an early Middle Campanian age (Ogg et al., 2004). Given Jinnah’s calculation of a general sedimentation rate of 8.2 cm/KA, the type locality of Diabloceratops (Last Chance skull) would date at ~79.57 Ma, well into the Middle Campanian. Thus, although younger than the Late Santonian to Early Campanian Menefee (Molenaar, 1983; Dyman et al., 1994), Santonian Milk River (Braman, 2002; Eaton, 2006) and Early Campanian lower Two Medicine (Rogers et al., 1993; Chinnery and Horner, 2007) faunas, the Wahweap would still be older than any of the known centrosaurine-bearing Judithian faunas of southern Alberta and Montana (Eberth et al., 1992; Brinkman et al., 1998; Sampson and Loewen, 2007, this volume). However, it is unlikely that the sedimentation rate was continuous from the base of the Wahweap Formation up into the base of the overlying Kaiparowits Formation, as proposed by Jinnah et al. (2007), because the capping sandstone member of the Wahweap Formation represents a reorganization of sediment dispersal in the region (Pollack, 1999; Pollock et al., 1999) and perhaps condensation (Eaton and Nations, 1991). Additionally, there are major faunal differences between the Wahweap and overlying Kaiparowits 24 Formation (Cifelli and Madsen, 1986; Cifelli, 1990a, b, c; Eaton et al., 1999; Eaton, 2002; Eaton and Kirkland 2003) and, with the recognition that the Aquilan Land Mammal Age is Santonian and not Campanian (Eaton, 2006), perhaps a distinct Middle Campanian “Wahweapian” Land Mammal Age should be recognized. The latest Middle Campanian Foremost Formation microvertebrate fauna appears to be distinctly different from that of the overlying Upper Campanian Dinosaur Park Formation in southern Alberta (Peng et al., 2001), adding some support to this concept. Given a condensed interval, or unconformity, near the contact between the Wahweap and Kaiparowits formations, the sedimentation accumulation rate in the lower part of the Wahweap Formation may have been significantly higher than that proposed by Jinnah et al. (2007). Therefore, the time difference between the Nipple Butte and Last Chance Skulls was probably significantly less that 0.5 million years. Comparisons Diabloceratops can be included within the Centrosaurinae on the basis of possessing a caudal narial process and a stepped suture between the squamosal and parietal (Dodson et al., 2004; Ryan, 2007a). Additionally, the morphology of its frontal fontanelle is shared by other centrosaurines (Dodson, et al., 2004). The long postorbital horns and small narial horn in D. eatoni are primitive character states within the Ceratopsidae as indicated by the ceratopsid sister taxon Zuniceratops (Wolfe and Kirkland, 1998; Wolfe, 2000; Wolfe et al., 2007; Ryan, 2007a). Diabloceratops and the recently described Albertaceratops (Ryan, 2007a) are the first centrosaurines discovered that have large postorbital horns and small narial horns. These 25 discoveries confirm predictions made after the discovery of Zuniceratops that long horned centrosaurines should be found in the fossil record. Diabloceratops eatoni exhibits several autapomorphies that are unique to currently described centrosaurines. Although a short, deep preorbital skull is characteristic of other centrosaurines (ex. Dodson et al., 2004), in Diabloceratops this shortening of the skull is even more readily apparent. Although an epinasal fused to the nasal horn is diagnostic of chasmosaurine ceratopsids, the presence of a distinct epinasal fused to the nasal rostral to the nasal horn is unique to Diabloceratops. As discussed below, an accessory antorbital fenestra is present in some chasmosaurines and more basal neoceratopsians. However, this character is known in no other centrosaurines. The skull roof is distinctive in rising in a steep vault at the base of the postorbital horns. Ryan (2007a) reports this character in Albertaceratops, but it does not appear to be so strongly developed. The jugals are elongate and inclined rostrally such that the posterior margin of the maxilla is completely exposed in lateral view. This character is developed rarely in Triceratops, as can be observed in DMNH 48617 (Hatcher et al., 1907; Carpenter, 2007). Diabloceratops has the largest epijugals of any known centrosaurine, and their blade-like shape and vertical orientation are distinctly different from the large conical epijugals developed in some chasmosaurines, such as Pentaceratops (ex. Lehman, 1993). The frill of Diabloceratops is completely different from all other centrosaurines in that it is erect and widest at its laterally directed squamosals narrowing to half its width caudally. Two elongate caudal spines are nearly as long as the entire frill. The parietal fenestrae are caudorostrally elongate (Figs. 4, 5, 13). Additionally, the epocipital on the lateral side of parietal decrease in size caudally whereas, the epoccipitals increase in size caudally or 26 maintain a relatively constant size in all other centrosaurines (fig. 13). Chasmosaurines typically decrease the size of the epoccipital along the lateral margin of the frill caudally, but in chasmosaurines this occurs along the margin of their elongate squamosals (ex. Dodson et al., 2004). We conducted a preliminary phylogenetic analysis of Diabloceratops in 2006, utilizing the data set developed by Ryan (2003) for his revision of the Centrosaurinae. This analysis indicated that Diabloceratops was the sister taxon of Albertaceratops and the other more derived centrosaurines, although its inclusion in the data set led to a significant loss of phylogenetic resolution among the more derived centrosaurines (Kirkland and DeBlieux, 2006). Further preparation of the lateral margin of the snout supports this result, but indicates that, in light of these new observations, further comparison with advanced, nonceratopsid neoceratopsians from Asia are needed to fully understand the phylogenetics of the Ceratopsidae. Merging the data sets for the more basal neoceratopsians (You and Dong, 2003; You and Dodson; 2004; Makovicky and Norrell, 2006; Chinnery and Horner, 2007) and the Ceratopsidae (Dodson et al., 2004; Ryan, 2007a) should be done, but is beyond the scope of this descriptive paper. Ornamentation of the adult centrosaurine frill is thought to be sexually selected for display and species recognition (Sampson et al., 1997) and has proven critical to understanding the phylogenetic relationships. Sampson et al. (1997) developed a nomenclature for designating proposed homologies in the epoccipitals of centrosaurines using a numbering system from the midline out (Fig. 13). Epoccipital 3 is a large spine projecting from the back of the frill in all genera except Centrosaurus, and Dodson et al. (2004) have proposed that this is an ambiguous autapomorphy for centrosaurines. Given 27 its distinctiveness, it is often referred to as the parietal spine. In this, we agree, but on examing the spine in Diabloceratops, we come to the conclusion that these large parietal spines may accrete by the fusion of multiple epoccipital ossifications, enlarging the spine through ontogeny. In this, it would be fundamentally different from the single step fusion that occurs at other epoccipital loci. Additionally, when considered with Albertaceratops (Ryan, 2007a), it appears that the parietal spine was the initial parietal ornamentation developed in centrosaurines, with all more derived centrosaurines developing a medially directed spine at the lateral margins of the parietal notch (process 2). Styracosaurus and Centrosaurus both develop a fold rostral to the parietal notch that variably develops with fusion of an epoccipital into a rostrally oriented spine (process 1). Thus, both processes 1 and 2 are derived characters of more restricted distribution (Ryan, 2007a). Given the discovery of Albertaceratops and Diabloceratops, the nomenclature used for describing the ornamentation of the frill should be reconsidered in light of phylogenetic patterns as well as ontogenetic patterns. Another feature of considerable importance is the presence of an accessory antorbital fenestra in the side of the skull behind the nasal opening at the front of the antorbital fossa. This fenestra is not present in the more advanced centrosaurines, but is present in Zuniceratops, where it is also bounded by the premaxilla, nasal, and maxilla (Wolfe et al., 2007). Two more basal species of protoceratopsid-grade neoceratopsians Bagaceratops (= Breviceratops, Lamaceratops, and Platyceratops) (Maryanska and Osmolska, 1975; Witmer, 1997; Sereno, 2000; Alifanov, 2003) and Magnirostris (You and Dong, 2003) have a similar accessory antorbital fenestra, where the nasal is excluded from the margin of the opening (Fig. 14). 28 The occurrence of Protoceratops hellenikorhinus with Magnirostris dodsoni at Bayan Mandahu, Inner Mongolia, China, suggests that these strata are a somewhat different age than the Barun Goyot Formation of Mongolia where Bagaceratops occurs (Maryanska and Osmolska, 1975; Lambert et al., 2001; You and Dong, 2003). Eberth (1993) has correlated the redbeds at Bayan Mandahu with the Djadokhta Formation of southern Mongolia, further suggesting that Magnirostris and Bagaceratops did not occur contemporaneously. Together with the presence of postorbital horns and elongate rostral bone, the synonymy of Magnirostris with Bagaceratops suggested by Makovicky and Norell (2006) is difficult to support. Lehman (1993) recognized a tiny accessory antorbital foramen at the junction of the premaxilla, nasal, and maxilla in Pentaceratops (ex. AMNH 1624) and in the skull of Agujaceratops (TMM 43098-1) described by Forster et al. (1993), although we have observed that preparation is such that it is visible only on the right side of skull. It is impossible to determine the presence of this feature in the poorly preserved type material of Agujaceratops mariscalensis, although its presence is suggested in the line art of the maxilla (Lehman, 1989). We noted this feature in fossil material representing a new chasmosaurine from the Kaiparowits Formation in Utah (Kaiparowits new taxon B, Sampson and Loewen, 2007), indicating its presence in all the southern chasmosaurines of the Late Campanian. We also observed that a tiny accessory antorbital foramen is present in individuals of Chasmosaurus (ex. AMNH 5401, TMP 81.19.175) with large brow-horns and is not present in any known specimens of Chasmosaurus russelli, Chasmosaurus belli, or Chasmosaurus irvinensis with reduced brow horns. Thus, the accessory foramen is lost within the well-established Chasmosaurus line of the northern 29 Western Interior (Holmes et al., 2001). The repeated loss of the accessory antorbital fenestra in more derived ceratopsids may have resulted from selection for a more solid facial area due to the stresses imparted by intraspecific grappling combat (Sampson, 1997). However, while the accessory antorbital fenestra is bordered by the premaxilla and maxilla in Bagaceratops and Magnirostris, the nasal contributes to the dorsal border of the accessory fenestra in Zuniceratops and in all ceratopsids, where it is recognized. Magnirostris also possesses small, but distinct, rugose, postorbital horns not present in any specimens of Bagaceratops (Fig. 14). Thus, Diabloceratops eatoni, together with Zuniceratops, provide substantial evidence that among all the known Asian protoceratopsians, Magnirostris is the sister taxon to the large horned ceratopsids of North America (Fig. 15). This repudiates the monophyly of the more derived protoceratopsid-grade neoceratopsians of Asia (You and Dodson, 2004; Makovicky and Norrell, 2006, Chinnery and Horner, 2007). Additionally, these hypotheses lead us to predict that, when more complete specimens of the central Asian advanced neoceratopsian Turanoceratops (Nessov et al., 1989; Sereno, 2000) are described, they will be found to have a well-developed accessory antorbital fenestra. Diabloceratops shares a number of features with the chasmosaurines. The large postorbital horns and small narial horn are well established as being primitive shared character states (Wolfe and Kirkland, 1998; Dodson et al., 2004; Ryan, 2007a). However, there are a number of other characters that are not recognized in any other centrosaurines. In particular, the caudal process of the premaxilla does not meet with the lacrimal in Diabloceratops or in any chasmosaurines. The closure of the accessory antorbital 30 opening in more derived centrosaurines may have resulted by the extension of this process across the dorsal side of the maxilla. The large epijugals in Diabloceratops is a character shared with many chasmosaurines. Although differing in position, the presence of an epinasal is shared only with chasmosaurines. These additional characters would also be shared primitive character states with the chasmosaurines, if our phylogenetic hypotheses were correct (Fig. 15). The Nipple Butte skull appears to be more mature than the Last Chance skull in that the occipital condyle is a bit larger, and the epoccipitals are fused into the margin of the frill. The caudally recurved tip of the postorbital horns in the type of Diabloceratops may indicate that this is a young adult individual (Horner and Goodwin, 2006, in press: Goodwin and Horner, 2007, this volume). The adult age of the type of Diabloceratops is suggested by the complete fusion of the nasals, a fused epinasal, and the exclusion of the supraoccipital from the foramen magnum (Horner and Goodwin, 2006). Also, the ectopterygoid is more fully fused to the maxilla in the Nipple Butte Skull forming little more than a roughened bulge for muscle attachment, whereas the ectopterygoid in the Last Chance skull exhibits a distinct sutural contact with the maxilla. However, in contradiction to the hypothesis that the Nipple Butte skull is more mature, the epijugal is not attached to the Nipple Butte skull. Additionally, the squamosal/parietal suture is open in both skulls. The surface morphology of ceratopsian periosteal skull bone has been used as a means of determining the relative ontogenetic age of individuals (Sampson et al., 1997; Tumarkin-Deratzin, 2003; Brown et al., 2007). Both specimens described here have bone with areas of smooth, mottled, and rugose surface textures that are associated with adult 31 specimens. No long-grained, striated bone indicative of juveniles is seen on either of these two specimens. Based on bone surface texture, along with other lines of evidence mentioned above, we propose that UMNH VP 16699 was fully adult but not an extremely old individual, based on that the lack of large areas of extremely rugose bone. The frill of UMNH VP 16704 generally displays more rugose bone, especially on the dorsal surface of the lateral parietal, than does the frill of UMNH VP 16699, a fact that fits well with other indications that this may have been an older individual. Finally comes the question as to the relationship between Nipple Butte and Last Chance skulls; does the Nipple Butte specimen represent Diabloceratops eatoni? The stepped squamosal suture and the presence of a robust postorbital horn indicate that the Nipple Butte skull represents a basal, long-horned centrosaurine (Kirkland et al., 2002; Ryan, 2003, 2007a; Kirkland and DeBlieux, 2007). Although there appear to be differences in the relative maturity of the two skulls, they both are about the same size and are the smallest known centrosaurines. The jugals are very similar in being elongate and inclined posteriorly with a dorsoventrally deep epijugal overlapping the suture between the jugal and quadratojugal. The rostral margin of the parietal fenestra of both skulls is relatively straight and the fenestra appears that it may taper posteriorly in both skulls. Nonetheless, there are important differences in the rostral portion of the frill. In all other centrosaurines (including the Nipple Butte skull) and in all chasmosaurines, the squamosal expands laterally (Fig. 16) so there is a notch between the back of the skull and frill that housed the external ear. In Diabloceratops eatoni, Zuniceratops, and more basal neoceratopsids, the notch is not developed, such that the posterior surface of the 32 quadrate and the ventral surface of the squamosal make a right or obtuse angle, in contrast with an acute angle seen in all other ceratopsids. Taken together, these observations would indicate that Diabloceratops eatoni is basal to the other known centrosaurines (Fig. 15). However, it is critical to note that, based on the presence of a presumed pathological opening on the squamosal above the infratemporal fenestra and the lack of a preserved right squamosal for comparison, it is possible that the square rostral margin of the lateral squamosal in UMNH VP 16699 may also be pathological, as noted in the description. The exposure of the base of the paraoccipital process laterally below the squamosal may reflect this pathology, except this condition is present in some specimens of Centrosaurus apertus; symmetrically in AMNH 5351 (type of Centrosaurus nasicornis) and asymmetrically in NMC 348 (type of Centrosaurus flexus). Additional definitive Diabloceratops material will be needed to determine whether the squared-off squamosal is pathological, so we hesitate to give much weight to this character at this time. Differences in the positioning of the epoccipitals across the squamosal-parietal suture are significant. Whereas differences in maturity would explain the variation in the development of these epoccipital in these two skulls, it would not account for the differences in their relative position. There is a large gap between the most rostral epoccipital on the preserved lateral margin of the parietal and the most caudal epoccipital on the right squamosal in the Last Chance skull, such that a missing epoccipital may well have straddled this suture as in many centrosaurines, such as Styracosaurus (Ryan, 2007b). In the reconstruction of this skull, Rob Gaston included an epoccipital in this position on the reconstructed right side of the frill (Fig. 17). In the Nipple Butte skull, 33 epoccipitals on the parietal and squamosal are closely placed to this suture, such that there would be no room for any intermediate epoccipital straddling this suture (Figs. 4, 10). The squamosal in the Nipple Butte skull appears to be similar in morphology to the older, and much larger centrosaurine (NMMNHS P-25052) from the Menefee Formation in New Mexico (Williamson, 1997) (Fig. 16). As the ornamentation of the frills in centrosaurines is critical taxonomically (Sampson, 1993, 1996; Dodson et al., 2004; Ryan, 2003, 2007a, b), it is unlikely that the Nipple Butte and Last Chance skulls represent the same species if not the same genus. Until more specimens of Diabloceratops eatoni are collected, it will be impossible to determine which of the many characters diagnosing the species currently represent characters that are variable within the species, diagnose the species, diagnose the genus, or are shared by as yet unknown sister genera. CONCLUSIONS Two species of basal centrosaurine ceratopsians are recognized from the lower Middle Campanian Wahweap Formation of southern Utah: Diabloceratops eatoni and cf. Diabloceratops. Of the many dinosaur taxa documented from microvertebrate sites in the Middle Campanian Wahweap Formation of southern Utah, Diabloceratops is the first dinosaur that has been described to species (Fig. 18). At present, Diabloceratops is the most southern and oldest diagnosable centrosaurine, although there are less complete, Late Campanian centrosaurines known from Coahuila, Mexico (Murray et al., 1960; Kirkland et al., 2000; Loewen et al., this volume) and southern Arizona (Heckert et al., 2003) and older. There is also an older and more southern centrosaurine fossil from the 34 Menefee Formation of northwestern New Mexico (Williamson, 1997). Together with Zuniceratops, Diabloceratops provides important supporting data regarding character states at the base of the Ceratopsidae and ceratopsid relationships with the known more basal neoceratopsians of Asia. ACKNOWLEDGMENTS All excavations were conducted under Bureau of Land Management (BLM) permit numbers UT-S-00-001, UT-EX-03-007, and UT-EX-05-026. Funding was provided by the BLM through assistance agreement JSA015002 and the UGS. Alan Titus is thanked for his efforts to facilitate this research at GSENM. Marietta Eaton and Dave Hunsaker at the GSENM are thanked for their assistance. Help in the field was provided by Bob and Linda Baldazzi, Jane DeBlieux, Walt Elkington, Terry “Bucky” Gates, Joe Gentry, Mike Getty, Martha Hayden, Don and Sheila Hughes, Mark Loewen, Tom Mellenthin, Andrew Milner, Sandy Mosconi, George Muller, Phil Policelli, Joshua A. Smith, Steve and Sally Stevenson, Alan Titus, Darrell and Terri Wade, Dave Wilcots, Bill and Arlene Yensen, David Zivcovic, Zion Helitack, and the UGS. Rob Gaston is thanked for his skillful molding, casting, and reconstruction of UMNH VP 16699. We thank Jim Gardener of the Royal Tyrrell Museum of Paleontology, Mike Getty of the Utah Museum of Natural History, Carl Mehling of the American Museum of Natural History, Tim Rowe of the Texas Memorial Museum, Kevin Seymour of the Royal Ontario Museum, Keiren Shepard of the Canadian Museum of Nature, and Tom Williamson of the New Mexico Museum of Natural History for the opportunity to study 35 their ceratopsian specimens. Hailu You and Xu Xing are thanked for arranging for JIK to study the holotype specimen of Magnirostris dodsoni IVPP V 12513. Discussions with Peter Dodson, Andrew Farke, Pete Makovicky, Lukas Panzarin, Mark Loewen, and Mike Ryan are appreciated. Scott Hartman suggested the generic name. Brad Wolverton's skillful rendering of Diabloceratops in figures 4A and 18 is appreciated. Reviews by Peter Dodson, Jennifer Cavin, Martha Hayden, Mike Lowe, and xx are appreciated. LITERATURE CITED Alifanov, V. R. 2003. 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A, Grand Staircase – Escalante National Monument with outcrop of Campanian Wahweap and Kaiparowits Formations. General location of Nipple Butte and Last Chance ceratopsian skulls indicated. B, Wahweap fauna mostly from Eaton et al. (1999). N = 57 identified taxa. Figure 2. Collection of the Nipple Butte Skull. A, Overview of site at top of the lower sandstone member of Wahweap Formation. Nipple Butte to southeast in background. B, Field sketch showing relationship of bone-bearing sandstone blocks. C, Dragging skull block toward road. D, Winching skull block up slope in middle mudstone member. E, Lifting skull block up for loading into truck. Figure 3. Collection of Last Chance Skull. A, North side of Reynolds Point with the gorge of Last Chance Creek in foreground. Star indicates location of skull. Arrowheads indicate member contacts of Wahweap Formation. Abbreviations: ls, base of lower sandstone member; mm, base of middle mudstone member; us, base of upper sandstone member; cs, base of capping sandstone member. B, Skull as first observed. C, Skull after surface clean-up. D, Rock-sawing the skull block. E, Airlifting the skull out of the backcountry to the road. Abbreviations: oc, occipital condyle; pb, parietal bar; rh, right horn; rm, impression of right maxilla. 48 Figure 4. Left lateral view of Diabloceratops eatoni holotype (UMNH VP 16699). A, Diagramatic representation of skull. B, Skull. Abbreviations: aaf, accessory antorbital fenestra; af, antorbital fenestra; ec, ectopterygoid; ej, epijugals; en, epinasal; j, jugal; l, lacrymal; it, infratemporal fenestra; m, maxilla; n, nasal; nh, nasal horn; np, caudal nasal process; oh, orbital horn; p, parietal; pal, palpebral; path, pathology; pb, parietal bar; pf, parietal fenestra; po; postorbital; pp, paraoccipital process; ps, parietal spine; pt, pterygoid; q, quadrate; qj, quadratojugal; r, rostral; s, squamosal; st, supratemporal fenestra; t, triangular process on parietal. Figure 5. Caudal and right lateral views of Diabloceratops eatoni holotype (UMNH VP 16699). A, Caudal view. B, Right lateral (medial) view. Figure 6. Detail of antorbital fossa of Diabloceratops eatoni (UMNH VP 16699) from cast specimen. Abbreviations: aaf, accessory antorbital fenestra; af, antorbital fenestra; j, jugal; l, lacrymal; m, maxilla; n, nasal; np, caudal nasal process; pal, palpebral. Figure 7. Skull roof of Diabloceratops eatoni. Blurred right side is reconstructed in this cast. Abbreviations: ej, epijugal; ff, frontal fontanelle; lam, caudal limit of jaw adductor muscle on parietal; oh, orbital horn; pb, parietal bar; pf, parietal fenestra; po, postorbital; sad, sulcus connecting frontal fontanelle with supratemporal fenestra; st, supratemporal fenestra. 49 Figure 8. Caudal view of rear of skull of Diabloceratops eatoni. Blurred right side is reconstructed. Abbreviations: bt, basitubera; ec, ectopterygoid; ej, epijugals; fm, foramen magnum; j, jugal; m, left maxilla; o, occipital condyle; q, quadrate; qj, quadradojugal; p, parietal; pb, parietal bar; pl, palatine; pp, paroccipital process; pt, pterygoid; s, squamosal; so, supraoccipital; IX-XII, cranial nerve openings. Figure 9. Right lateral view of Diabloceratops eatoni braincase (UMNH VP 16699). Abbreviations: bp, basipterygoid process; bt, basitubera; cc, path for carotid artery; cff, area collapsed into frontal fontanelle; e, “eustachial” canal of Hatcher et al., (1907); fo, fenestra ovalis; lb, laterosphenoid buttress; m, left maxilla; mqc, medial condyle of left quadrate; oc, occipital condyle; oh, cross-section of right postorbital horn; pb, parietal bar; pl, right palatine; pp, paroccipital process; pt, pterygoid; stf, supratemporal fenestra; II-XII, cranial nerve openings. Figure 10. Preserved frill of Nipple Butte skull (UMNH VP 16704) from block 1. A, Dorsal view. B, Ventral view. Figure 11. Additional elements of Nipple Butte skull (UMNH VP 16704) from block 1. A, Medial view of braincase and preserved partial left palate. B, Ventral view of braincase and preserved partial left palate. C, Detail of medial view of palate (Fig. 11A). D, Lateral view of postorbital horn fragment. E, Distal view of postorbital horn fragment. F, Lateral view of maxilla and pterygoid in Figs.11A, B. Abbreviations: bp, basipterygoid process; bt, basitubera; e, “eustachial” canal of Hatcher et al., (1907); ec, 50 ectopterygoid; m, right maxilla; oc, occipital condyle; pp, paroccipital process; pt, pterygoid. Figure 12. Elements of Nipple Butte skull (UMNH VP 16704) from block 3 and partial right maxilla from block 1. A, preserved right side elements from block 3. B, Caudolateral portion of right maxilla and ectopterygoid from block 1. Abbreviations: ec, ectopterygoid; ej, sutural surface for epijugal; j, jugal; l, lacrymal; m, ascending process of right maxilla; o, orbit; pal, palpebral. Figure 13. Parietals of various genera of centrosaurines with epoccipital nomenclature developed by Sampson et al. (1997) indicated by numbers. A, Diabloceratops. B, Albertaceratops. C, Pachyrhinosaurus. D, Achelousaurus. E, Einiosaurus. F, Centrosaurus. G, Styracosaurus. Gray areas indicate actual bone preserved. Scale bars = 10 cm. Modified after Sampson et al. (1997) and Ryan (2003). Figure 14. Holotype of Magnirostris dodsoni in the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP V 12513) missing both squamosals and parietals with reconstructed left jugal, left quadrate, and partial left postorbital. A, Right side. B, Rostral view. C, Left side. D, Dorsal view. E, Caudal view. F, Ventral view. G, Left oblique view of nasal and orbital area. Left orbital horn partially preserved and depressed along fracture. 51 Figure 15. Hypothesized ceratopsian family tree plotted against a linear time scale in millions of years ago (MYA) and Cretaceous rocks in the Grand Staircase – Escalante National Monument. Note: frill is not preserved on figured skull of Magnirostris. Francois Gohier is thanked for many of the ceratopsian skull photographs. Figure 16. Comparison of Santonian to Middle Campanian centrosaurine squamosals from the southwestern United States. A, Last Chance right squamosal (UMNH VP 16699). B, Nipple Butte right squamosal (UMNH VP 16702). Arrowheads indicate positions of epoccipitals. C, Menefee squamosal (NMMNHS P-25052). Solid arrows indicate position of epoccipitals. Open arrows indicate position of suspect apparent epoccipitals. Drawn in same orientation. Figure 17. Reconstructed skull of Diabloceratops eatoni. A, Dorsal view. B, Oblique lateral view. C, Caudal view. D, Rostral view. Figure 18. Life reconstruction of the head of Diabloceratops eatoni by Brad Wolverton. 52 53 Fig. 1 54 Fig. 2 55 Fig. 3 56 Fig. 4 57 Fig. 5 58 Fig. 6 59 Fig. 7 60 Fig. 8 61 Fig. 9 62 Fig. 10 63 Fig. 11 64 Fig. 12 Fig. 13 65 Fig. 14 66 Fig. 15 Fig. 16 67 Fig. 17 68 Fig. 18 69