Artwork showing the relative scale of humans and Euoplocephalus. This animal from the Late Cretaceous period, 76 million years ago, belonged to a diverse group of armoured dinosaurs called (after their prototype) ankylosaurids. Euoplocephalus was the second largest animal from this group (after Ankylosaurus), and grew to lengths of around 5.5 m (18 ft). Like most ankylosaurs, it was covered in bony plates and equipped with a massive club at the end of its tail, to defend itself from and deter predators.