Dentary
Irregular bone, part of the skull (axial skeleton)
Also known as: Lower jawbone
Classification
Irregular bone, part of the skull (axial skeleton)
Dimensions
Varies immensely depending on the species, ranging from a few centimeters in small fish or frogs to over a meter in large mammals and reptiles, generally elongated and curved.
Key Features
Look for a curved, arching shape featuring a row of tooth sockets or tiny teeth along the inner edge, often hollow or trough-like with porous textures at the tapered ends.
Similar Bones
Can sometimes be confused with ribs due to the curved shape, but a jawbone stands out because it features distinct tooth sockets or a grooved biting edge rather than the smooth, uniform ends of a rib.
Across Species
In mammals, the lower jaw is a single solid bone known as the dentary, equipped with sockets for teeth. In contrast, reptiles and birds retain a lower jaw made up of several distinct smaller bones fused together, a fascinating evolutionary holdover from ancient ancestors.
Evolutionary History
Over millions of years, the vertebrate lower jaw underwent a dramatic transformation. Early jawed fish possessed jaws made of multiple bones. In the lineage leading to mammals, the lower jaw simplified into just one dominant bone while several of the leftover jaw bones migrated into the inner ear to help us hear.
Photography Tips
Place the bone flat against a solid, contrasting background like a piece of dark paper. Use natural side lighting to highlight the texture of the tooth row and capture the entire curve from a top-down view with a small ruler for scale.