The tetanurans (Tetanurae, or “stiff tail”) are regarded as a sister group of the ceratosaurs; they are considered to be all theropods more closely related to modern birds than to the ceratosaurs. The tetanurans were a large and diverse group, comprising many species, including most of the well-known theropods. The unique characteristics of this group include a special row of teeth, a large pubic boot, the presence of a large opening in front of the jaw, and a rear half of the tail stiffened by interlocking, rod-like projections of vertebrae. The tetanurans also had a three-fingered hand. Many popular dinosaurs are tetanurans, including Archaeopteryx, Allosaurus, Oviraptor, Spinosaurus, Tyrannosaurus, Velociraptor, and all species of modern bird.