armoured North American dinosaur of the Late Cretaceous Period (99 million to 65 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 (dinosaur) 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.