Euoplocephalus, (genus Euoplocephalus), armoured North American dinosaur of the Late Cretaceous Period (99.6 million to 65.5 million years ago). Like its close relative Ankylosaurus and the more distantly related Nodosaurus, Euoplocephalus was a massive animal that likely weighed more than two tons. Euoplocephalus differed from these and most other ankylosaurs in having a bone that protected the eyelid. The teeth, as in all ankylosaurs, were limited to a single curved row and were used to eat plants.