A new parasaurolophin dinosaur (Hadrosauridae: Lambeosaurinae) from the Oldman Formation of southern Alberta

This is the authors' abstract. We don't add key points for this paper.

Lambeosaurines are abundant in the Dinosaur Park Formation of Alberta, but are poorly known from the underlying Oldman Formation (Upper Cretaceous: Campanian). A new partial skull roof and braincase from the Comrey Sandstone Zone (middle Oldman) at the Milk River Ridge Reservoir locality in southern Alberta represents the first diagnostic material of an adult lambeosaurine from this formation. Derived characters of the frontal platform and braincase (including the steeply inclined frontal platform, boomerang-shaped dorsal surface of the frontals, and pendent alar processes of the basisphenoid) support the referral of this specimen to Parasaurolophini, as the stratigraphically lowest specimen with the skull roof and braincase preserved. The recognition of a new taxon is supported by a unique combination of characters, some resembling the inferred plesiomorphic condition for corythosaurians, including a triangular plateau on the parietal separating the interfrontal process from the sagittal crest, and the anterolaterodorsal orientation of the postorbital process of the laterosphenoid. Despite the large size and fused interfrontal contact, the prefrontal–postorbital contact is not strongly elevated, and the posterior margin of the frontal platform does not overhang the parietal, resembling the condition described in an immature Parasaurolophus from Dinosaur Provincial Park, and providing support for heterochrony in the evolution of the parasaurolophin skull roof. As one of relatively few diagnostic Albertan hadrosaurids older than the Dinosaur Park Formation, the new taxon provides significant new data on the diversification of Corythosauria, and the evolution of hadrosaurid communities in Laramidia.