iguanodont

The skulls of iguanodonts accommodated still larger jaw muscles, but the cheek teeth were less regular and compacted than in the primitive ornithopods and consequently did not occlude as uniformly. Both the premaxillaries and the predentary were toothless but probably were sheathed in horny beaks.

…rise to the more advanced iguanodontids and hadrosaurs, which spent most of their time on all fours. The iguanodontids were medium-sized to large dinosaurs with the specialized grinding teeth typical of advanced ornithopods. The largest and best-known species, Iguanodon, reached a length of nine metres.