First occurrence of <i>Daspletosaurus horneri</i> (Tyrannosauridae, Tyrannosaurinae) in the Dinosaur Park Formation of Dinosaur Provincial Park, Alberta (Treaty 7 Territory)

The upper Campanian tyrannosaurine <i>Daspletosaurus horneri</i> was originally described based solely on specimens from the Two Medicine Formation of Montana, U.S.A.. Here, a taxonomic reassessment of a stratigraphically high occurrence of a <i>Daspletosaurus</i> specimen, CMN 350, from the Dinosaur Park Formation provides the first evidence of <i>D. horneri</i> within Alberta, Canada. CMN 350 was originally referred to the species <i>D. torosus</i>, but re-examination of the cranial morphology of this specimen revealed characteristics more similar to those of <i>D. horneri</i>. These characteristics include an inflated lacrimal horn that does not extend to the medial margin of the bone, a medial pneumatic recess opening of the lacrimal that is dorsoventrally tall and mediolaterally narrow, and a distinct lateral bow of the dentary. The referral of CMN 350 to <i>D. horneri</i> offers valuable insight into intraspecifically variable characteristics of the skull and aided in the amended species diagnosis. Furthermore, the recognition of <i>D. horneri</i> within the uppermost biozone of the Dinosaur Park Formation, 49 m above the underlying Oldman Formation contact, supports system-wide faunal turnover within the formation and extends the known latitudinal range of this taxon to approximately 350 km.