Ankylopollexia is a clade of herbivorous iguanodontian dinosaurs that lived from the Late Jurassic to Late Cretaceous in all continents. Some members include Camptosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". The Ankylopollexia was named by Paul Sereno in 1986 to denote the group within the Iguanodontia that includes the Camptosauridae and the Styracosterna. The name means "stiff thumbs", referring to a possible synapomorphy, possessing a conical thumb spine. Ankylopollexians were generally large animals, and some (such as Shantungosaurus, which measured up to 50 ft (15 m) in length and weighed up to 8 tons) equaled the largest carnivorous dinosaurs in size.