Anatomy of the neornithischian dinosaur Parksosaurus warreni (Parks, 1926) from the Upper Cretaceous (lower Maastrichtian) Horseshoe Canyon Formation of Alberta, Canada

The fossil record of Late Cretaceous non-hadrosaurid neornithischians from the Western Interior of North America is sparse. Parksosaurus warreni is an early Maastrichtian taxon currently known only from a skull and much of the associated postcranial skeleton and a referred isolated tooth from the Horseshoe Canyon Formation of Alberta, Canada. This article presents a detailed anatomical account of the holotype of this dinosaur following extensive additional preparation of the holotype and provides photographs of the postcranial elements for the first time. The premaxilla has a dorsoventrally deep posterolateral process, which overlaps the maxilla. The antorbital fenestra is small and teardrop-shaped. The lingual surfaces of dentary teeth bear nine or 10 vertically extending ridges that terminate in apical denticles. The suprascapula is mineralized or ossified. The dorsal margin of the ischium is posterodorsally concave at mid-length. The greater and lesser trochanters of the femur are not separated by a distinct cleft. The pendent fourth trochanter is placed on the proximal half of the femur. The more distal caudal vertebrae have greatly elongated prezygapophyses, which, together with a basket of ossified tendons ensheathing the caudal vertebrae, indicate that the tail may have functioned as a dynamic stabilizer during locomotion. The substantial new anatomical information from the holotype and only known skeleton of Parksosaurus warreni will allow more detailed comparisons to other closely related taxa and facilitate further discussions of unresolved aspects of the interrelationships of neornithischian dinosaurs.