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141 9 A New Pachyrhinosaurus-Like Ceratopsid from the Upper Dinosaur Park Formation (Late Campanian) of Southern Alberta, Canada MICHAEL J. RYAN, DAVID A. EBERTH, DONALD B. BRINKMAN, PHILIP J. CURRIE, AND DARREN H. TANKE in 2001, an almost complete, but disarticulated, adultsized centrosaurine ceratopsid (TMP 2002.76.1) with a pachystotic nasal boss and deeply excavated bosses over the orbits on each postorbital was collected from the transgressive Dinosaur Park Formation (DPF) at Dinosaur Provincial Park (DPP) near Iddesleigh, Alberta. Surficial bone texture indicates that the specimen was an old, mature individual. Pathological deformations are present in the anterior parietal bar and in many of the phalanges. Unfortunately, the typically diagnostic posterior parietal was not recovered, hindering a definitive identification of the specimen. A restricted phylogenetic analysis of Centrosaurinae produced an unresolved trichotomy of (TMP 2002.76.1 + Achelousaurus + Pachyrhinosaurus). TMP 2002.76.1 occurs near the top of the DPF in a stacked channel succession that cuts out the lowest coal of the 15 m thick Lethbridge Coal Zone. Dates from bentonites that bracket this interval suggest an age of 75.1 Ma, making TMP 2002.76.1 the first occurrence of a pachyrhinosaur ceratopsid in the fossil record. Introduction Centrosaurine ceratopsids are known primarily from the northern Upper Cretaceous biogeographic zone, although they are now known to have been present as far south as Mexico (Sampson and Loewen this volume), and Pachyrhinosaurus sp. is known from Alaska (Fiorillo et al. this volume). In regions with good fossil records (e.g., the Dinosaur Park Formation of Alberta and the Two Medicine Formation of Montana), centrosaurs appear to have undergone rapid stratigraphic replacement on the order of approximately every 0.5 Ma (Ryan and Evans 2005; Sampson and Loewen this volume). The last centrosaurines to appear in the fossil record are the clade of ‘‘pachyrhinosaurs’’ (Pachyrhinosaurus + Achelousaurus) distinguished by having large, pachystotic, boss-like nasal ornamentation and highly modified postorbital ornamentation, that, while usually described as being a ‘‘boss,’’ is more typically a wide, thin-floored, irregularly excavated depression. Pachyrhinosaurus canadensis was first described by C. M. Sternberg (1950) based on material collected from the St. Mary’s River Formation (Late Cretaceous) of southern Alberta from badlands along the north side of the Little Bow River and from the limited exposures at Scabby Butte. Additional material was collected from the Scabby Butte bonebed in 1957 by Wann Langston, Jr. (1975), as well as from the Horseshoe Canyon Formation along the Red Deer River in the Drumheller Valley. Starting in 1986 the Royal Tyrrell Museum of Palaeontology (then the Tyrrell Museum of Palaeontology) has collected Pachyrhinosaurus n. sp. (Currie et al. 2008) material from at least one monodominant bonebed in the Wapiti Formation near Grande Prairie, Alberta. A second bonebed in the same region may produce a different species of Pachyrhinosaurus (Fanti and Currie 2007). Pachyrhinosaurus material has 142 ryan, eberth, brinkman, currie, & tanke FIGURE 9.1. Locality map. TMP 2002.76.1 occurs at the southeastern margin of Dinosaur Provincal Park, Alberta. Inset shows the location (star) relative to Alberta. also been collected from northern Alaska (Nelms and Clemens 1989; Fiorillo 2004; Fiorillo et al. this volume). To date, the geologically oldest pachyrhinosaur has been Achelousaurus from the Two Medicine Formation of Montana (approximately 74.0 Ma; Sampson 1995; Sampson and Loewen this volume). It differs from Pachyrhinosaurus is having a nasal boss that does not contact the postorbitals, and having a less excavated form of the postorbital boss. Achelousaurus replaces Styracosaurus ovatus in that formation, and occurs approximately 1.0 Ma later than the last occurrence of Styracosaurus albertensis (Ryan and Evans 2005; Sampson and Loewen this volume) from the Dinosaur Park Formation of Alberta. We describe here a new pachyrhinosaur from the Dinosaur Park Formation of Dinosaur Park (Fig. 9.1), Alberta, which is now the geologically oldest pachyrhinosaur known, and discuss its implications for centrosaurine paleoecology. Institutional Abbreviations. AMNH: American Museum of Natural History, New York; MOR: Museum of the Rockies, Bozeman; TMP: Royal Tyrrell Museum of Palaeontology, Drumheller. Anatomical Abbreviations. A: angular; AF: antorbital fenestra; AG: groove for angular; AR: ascending ramus; ART: articular; D: dentary; EJ: epijugal; G: glenoid; J: jugal; JC: surface for jugal; L: lacrimal; M: maxilla; N: nasal; NB: nasal boss; O: orbit; P: parietal; PC: pterygoid contact; PD: predentary; PM: premaxilla ; PNR: posterior raised ridge of nasal boss; POA: anterior margin of postorbital ornamentation; POB: posterior margin of postorbital ornamentation; POP: postorbital process ; PP: pathological pit?; PS...

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