Parksosaurus (meaning "William Parks's lizard") is a genus of neornithischian dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada.

[4] Paleontologist William Parks described skeleton ROM 804 in 1926 as Thescelosaurus warreni, which had in 1922 been discovered in what was then called the Edmonton Formation near Rumsey Ferry on the Red Deer River.

Like Thescelosaurus, Parksosaurus had a relatively robust hindlimb, and an elongate skull without as much of an arched shape to the forehead compared to other hypsilophodonts.

[12] Cladogram based in the phylogenetic analysis of Rozadilla et al., 2015: Hypsilophodon Thescelosaurus Gasparinisaura Morrosaurus Trinisaura Macrogryphosaurus Notohypsilophodon Talenkauen Anabisetia Parksosaurus Kangnasaurus Rhabdodontidae Tenontosaurus Dryomorpha The cladogram below results from analysis by Herne et al., 2019, which placed Parksosaurus as the most basal member of Ornithopoda.

[13] Heterodontosauridae Eocursor Thyreophora Lesothosaurus Agilisaurus Hexinlusaurus Yandusaurus Nanosaurus Haya Jeholosaurus Changchunsaurus Orodromeus Koreanosaurus Zephyrosaurus Yueosaurus Thescelosaurus Marginocephalia Parksosaurus Talenkauen Macrogryphosaurus Gasparinisaura Galleonosaurus Leaellynasaura Anabisetia Diluvicursor Hypsilophodon Rhabdodontidae Muttaburrasaurus Tenontosaurus Dryomorpha Parksosaurus is known from the base of Unit 4 of the Horseshoe Canyon Formation,[14] which dates to about 69.5 million years ago.

[16] The Horseshoe Canyon Formation is interpreted as having a significant marine influence, due to an encroaching Western Interior Seaway, the shallow sea that covered the midsection of North America through much of the Cretaceous.

[9] Paul in 2010 suggested that the long toes were an adaptation for walking over mud or clay near rivers and that the strong arms were used for burrowing.