[[Image:Edmontosaurus_skull.jpg|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,<ref name="Fierstine1968"/><ref name="AlvaradoOrtega2010"/> and two dinosaur groups, ornithischians and ornithuromorph birds.<ref name="Bailleul2019"/>
A predentary is found in all but perhaps the earliest ornithischian dinosaurs. Its occurrence led Othniel Marsh to propose naming the group Predentata,<ref name="Marsh1894"/> though this is now considered a synonym of Ornithischia.<ref name="Norman2022"/> 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.<ref name="Nabavizadeh2016"/> The toothless, beaked tip of the dentary in silesaurids may have been a predecessor of the ornithischian predentary.<ref name="Ferigolo2007"/><ref name="Norman2022"/>
The avian predentary arose in the clade Ornithuromorpha,<ref name="Bailleul2019"/> and is absent from earlier bird lineages such as enantiornitheans and ''Archaeopteryx''.<ref name="Zhou2011"/> It has been interpreted as a sesamoid bone.<ref name="Bailleul2019"/> Members of Neornithes, the group containing all modern birds, lack a predentary, unlike other ornithuromorphs, possibly because the fusion of the mandibular symphysis and loss of teeth rendered the predentary unnecessary.<ref name="Crane2025"/> Due to the independent origins of the predentary in ornithischians and birds, the avian predentary has alternatively been called the '''intersymphyseal ossificiation''',<ref name="O'Connor2009"/> although this term is not entirely appropriate because it is not strictly intersymphyseal in position.<ref name="Bailleul2019"/>
An ossified predentary has arisen in two lineages of fish, the extinct Saurodontidae and the extant Istiophoridae (marlin), and a cartilaginous pre-mandibular element occurs in several other groups.<ref name="Bardack1969"/> The istiophorid predentary differs from other predentaries in bearing denticles.<ref name="Bardack1969"/>
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{{Tetrapod osteology|S.}} Category:Dinosaur anatomy