Mandible
Irregular bone, part of the core skull structure
Also known as: Lower jawbone
Classification
Irregular bone, part of the core skull structure
Dimensions
Varies widely from a few inches in small rodents to over a foot in large grazing mammals, featuring an elongated horizontal body holding teeth and a tall vertical back portion for muscle attachment.
Key Features
Look for a long, heavy trough-shaped bone holding a row of complex, flat-topped grinding teeth. The back end rises up into distinct high points or hooks designed for powerful chewing muscles, while the front end tapers off.
Similar Bones
Can be confused with the upper jaw, but the lower jaw is always a single movable bone with a tall back section. Upper jaws are fused directly into the main skull structure and rarely wash up as a single curved bar with teeth.
Across Species
In herbivores like deer and cows, the jaw features a long, toothless gap at the front followed by flat, ridged grinding teeth suited for chewing tough plant matter. Carnivores have shorter, deeper jaws with prominent canines and shearing teeth designed for catching and slicing prey. Birds lack a heavy bone here entirely, having evolved a lightweight beak instead.
Evolutionary History
The lower jaw underwent one of the most dramatic transformations in vertebrate history. In early fish and reptile ancestors, the lower jaw was made of multiple smaller bones. Over millions of years through the evolution of mammals, most of these smaller bones shrank and migrated into the inner ear to help us hear, leaving the single main bone we see today.
Photography Tips
Place the jaw flat on a solid, neutral-colored background. Take shots from the side to clearly show the full profile and tooth row, and a top-down view to capture the shape and width of the teeth.