The synonymy of the ankylosaurid dinosaur Scolosaurus with Euoplocephalus has been widely accepted since the 1970s. However, Scolosaurus cutleri exhibits differences which separate it from Euoplocephalus tutus and Dyoplosaurus acutosquameus. Although the holotype of Euoplocephalus is fragmentary, several other specimens can be reliably referred to this taxon and thus used for comparison. Scolosaurus differs from Euoplocephalus in cervical half-ring, osteoderm, and forelimb morphology. Scolosaurus differs from Dyoplosaurus primarily in pelvic morphology and osteoderm shape. Recognition of Scolosaurus as a valid taxon adds to the growing concept that the Upper Cretaceous ankylosaurid fauna of North America was more diverse than previously thought.