a troodontid, a classification which stands today. Since 1969 Polyodontosaurus has been considered a synonym of Stenonychosaurus, and later its senior synonym Troodon. Polyodontosaurus is potentially a synonym of the taxon Latenivenatrix, named in 2017, but they may come from separate regions of the formation. Van der Reest & Currie in 2017 determined that due to the lack of sufficient material in the holotype, and that the dentaries of troodontids to not bear unique, autapomorphic features, Polyodontosaurus was a nomen dubium, and could not be considered senior synonym of Latenivenatrix. Below is the phylogenetic analysis of van der Reest & Currie (2017). Polyodontosaurus has been considered a synonym of the "Two Medicine troodontid" and Latenivenatrix previously. Paleoecology The single specimen of Polyodontosaurus was found in the central level of the Dinosaur Park Formation, and was a member of a diverse and well-documented fauna of prehistoric animals that included such well-known dinosaurs as the horned Centrosaurus, Styracosaurus, and Chasmosaurus, fellow duckbills Prosaurolophus, Gryposaurus, Corythosaurus, and Parasaurolophus, tyrannosaurid Gorgosaurus, and armored Edmontonia and Euoplocephalus. The Dinosaur Park Formation is interpreted as a low-relief setting of rivers and floodplains that became more swampy and influenced by marine conditions over time as the Western Interior Seaway transgressed westward. The climate was warmer than present-day Alberta, without frost, but with wetter and drier seasons. Conifers were apparently the dominant canopy plants, with an understory of ferns, tree ferns, and angiosperms. References Troodontids Late Cretaceous dinosaurs Nomina dubia Cretaceous dinosaurs of North America