Ankylosaurus magniventris is an iconic dinosaur species often depicted in popular media. It is known from relatively fragmentary remains compared with its earlier and smaller relatives such as Euoplocephalus and Anodontosaurus. Nevertheless, the known fossils of Ankylosaurus indicate that it had diverged significantly in cranial and postcranial anatomy compared with other Laramidian ankylosaurines. In particular, the dentition, narial region, tail club, and overall body size differ substantially from other Campanian–Maastrichtian ankylosaurines. We review the anatomy of this unusual ankylosaur using data from historic and newly identified material and discuss its palaeoecological implications.