Calvarius is a genus of styracosternan ornithopod from the Late Cretaceous of Spain. The name alludes to its chronostratigraphic proximity to the extinction event that wiped out the non-avian dinosaurs at the end of the Cretaceous. The highly modified metatarsal that is known from shows an example of convergent evolution, as it is more similar to non-iguanodontian ornithopods than to other styracosternans. It is thought that this is due to fulfilling a niche in its island habitat, resulting in Calvarius becoming a small-bodied animal, capable of rapid locomotion.