Predentary

right|thumb|300px|Edmontosaurus [[skull with a visible predentary]] A predentary is an ossification situated on the front of the lower jaw, which extended the dentary (the main lower jaw bone). A predentary bone has evolved independently in two groups of teleost fish, Istiophoridae and Saurodontidae, and two dinosaur groups, ornithischians and ornithuromorph birds.

A predentary is found in all but perhaps the earliest ornithischian dinosaurs. Its occurrence led Othniel Marsh to propose naming the group Predentata, though this is now considered a synonym of Ornithischia. The predentary coincided with the premaxilla in the upper jaw. Together, they formed a beak-like apparatus used to clip off plant material. In ceratopsian dinosaurs, it opposes the rostral bone. The predentary would have allowed the dentaries to move slightly independently of each other, aiding chewing. The toothless, beaked tip of the dentary in silesaurids may have been a predecessor of the ornithischian predentary.