prearticular

The prearticular is a bone of the mandible (lower jaw) found in various jawed vertebrates, particularly in fossil groups and early sarcopterygian and amniote lineages. The name reflects its typical position near the jaw joint, usually on the inner surface of the lower jaw, and its relation to the articular bone.

In many taxa, the prearticular forms part of the mandibular arcade and contributes to the posterior and medial aspects of the jaw joint. Its exact contacts vary among species: in some forms it lies medial to the articular and interfaces with the articular or with other nearby jaw bones such as the dentary, surangular, or splenial. The bone may participate in joint surfaces or serve as a site for muscle attachment and for transmitting mechanical forces during jaw closure.

Functionality and development of the prearticular are tied to the broader evolution of the jaw. In early jawed vertebrates, a more complex lower jaw with multiple articulated elements—including the prearticular—supported diverse feeding strategies. Over evolutionary time, many lineages show reduction, fusion, or loss of the prearticular, and in mammals the traditional articular–quadrate jaw joint was replaced by a dentary–squamosal joint, with some ancestral elements reorganized or no longer present as separate bones.

Because the presence and morphology of the prearticular vary considerably across taxa, it is largely a feature described in comparative anatomy and paleontology rather than a universal component of modern vertebrate jaws. See also articular, quadrate, dentary, and jaw joint.