Hainosaurus pembinensis, a new species of tylosaurine mosasaur, is described from the Pembina Member of the Pierre Shale (Campanian, Late Cretaceous) of Manitoba. Hainosaurus differs from Tylosaurus in having a larger number of vertebrae anterior to the chevron-bearing caudals, a greater length of the femur relative to the humerus, and a greater length of the external nares. Hainosaurus pembinensis is distinguished from other species of this genus by its long supratemporal fenestra and homodont dentition. This is the first record of Hainosaurus from North America and represents both a geographic and stratigraphic range extension for the genus.

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