The holotype of Dyoplosaurus acutosquameus Parks, 1924 (=Euoplocephalus tutus Lambe, 1910), represents one of the most complete ankylosaurid specimens collected to date. It consists of a partial skull roof, four mandible fragments with two teeth in situ, portions of postcranial armor (some in situ), skin impressions, articulated post-thoracic vertebrae, ten partial thoracic ribs, a partial left ilium, both ischia, and tail club, and associated right radius, left metacarpal IV, femur, tibia, fibula, and pes. We provide a detailed redescription of this material as well as comparisons with other ankylosaurid specimens referred to E. tutus. The synonymy of the genus with Euoplocephalus is not supported, and Dyoplosaurus is a valid taxon. It is possible that the fragmentary nature of the holotype of Euoplocephalus leads to the inference that the diversity of Late Cretaceous North American ankylosaurids is lower than it actually is. As such, it might be necessary to look beyond traditional cranial characters in order to accurately appraise the number and nature of various ankylosaurid taxa.