In 1995, the Royal Saskatchewan Museum excavated a partial skeleton first discovered a year prior by a local farmer from a hill located northwest of Herbert Ferry, Saskatchewan. The skeleton was found articulated and consists of a "moderately complete" skull, a largely complete vertebral column, limb bones, and bones of a smaller mosasaur as stomach content; it was curated into the museum as RSM P2588.1 and nicknamed "Omācīw" (meaning "hunter" in Cree). In 2006, Timon Bullard of the University of Alberta studied the specimen in his Master of Science thesis. At the time, the Omācīw fossil was still in preparation and Bullard was only able to examine the right side of the skull. However, he identified that the fossil represented a new species of "Tylosaurus" and suggested that it be named "Tylosaurus saskatchewanensis" in reference to its type locality. Bullard's thesis was never published but subsequently published studies recognized "T. saskatchewanensis" as a valid species despite technically never having been formally described. In 2018, Bullard co-authored a multi-author study led by Jiménez-Huidobro which formally described Omācīw, which by then was more fully prepared, and confirmed its identity as a distinct species.