Mandible
Irregular bone of the facial skeleton
Also known as: Jawbone
Classification
Irregular bone of the facial skeleton
Dimensions
Varies widely by species, ranging from a few inches in small mammals to several feet in large herbivores and carnivores, characterized by a distinct curved or U-shape.
Key Features
Look for a smooth, sweeping curve resembling a horseshoe or a boomerang. One end typically features a vertical upward rise or a rounded knob that once connected to the skull, while the curved body often shows sockets or a rough upper edge where teeth were anchored.
Similar Bones
Ribs also feature a gentle curve, but ribs are generally more slender, twisted along their length, and lack tooth sockets or the broad upward extensions found at the ends of a jawbone.
Across Species
In mammals, the jawbone is a single solid piece on each side that holds the lower teeth, whereas reptiles and birds have multiple smaller bones making up the lower jaw. Herbivores like deer and horses have wide, flat surfaces for grinding tough plant matter, while carnivores have sharp locking joints designed for gripping and slicing meat.
Evolutionary History
The mammalian jawbone has a fascinating deep-time origin. In early ancestral vertebrates, the lower jaw was composed of several smaller bones. Over millions of years of evolution, most of these bones migrated away from the jaw and shrank to become the tiny hearing bones inside the mammalian ear, leaving the single robust bone we recognize today.
Photography Tips
Place a coin or ruler next to the bone for scale. Take a top-down shot with bright, even natural light to highlight the curve and any remaining tooth sockets, and take a second side-angle view to show the height and thickness of the bone.