Mandible
Irregular Bone and part of the axial skeleton
Also known as: Lower Jaw Bone
Classification
Irregular Bone and part of the axial skeleton
Dimensions
The mandible typically displays an elongated, curved shape with a thicker front edge that thins toward the back. Small mammal mandibles can range from a fraction of an inch to several inches long, maintaining a delicate, arc-like profile.
Key Features
The mandible is easily identified by its distinct 'U' or 'V' shape when both sides are joined. Look for a row of small hollow sockets or remaining teeth along the top edge, a smooth curved underside, and a flared, flat plate at the back corner where it attaches to the skull.
Similar Bones
This can sometimes be confused with a curved rib bone. However, a jaw bone will almost always feature tooth sockets or ridges along one side and a complex, widened hinge at one end, unlike the relatively uniform and simple ends found on ribs.
Across Species
In the animal kingdom, the mandible is a marvel of adaptation. While mammals have a single bone on each side of the lower jaw, reptiles and birds have multiple bones that hinge together. In predators like cats or weasels, the bone is sturdy with deep pockets for strong muscle attachment, whereas in rodents, the jaw is designed for a sliding forward-and-back motion to facilitate gnawing.
Evolutionary History
The story of the jaw bone began hundreds of millions of years ago when the front-most gill arches of ancient fish transformed into biting structures. Over deep time, the mammalian lineage seen today simplified the lower jaw into a single bone, which allowed for more powerful chewing and cleared the way for the smaller, former jaw bones to migrate into the ear to improve hearing.
Photography Tips
To get the best identification shots, place the bone on a flat, neutral surface. Take one photo directly from the side to show the curve, and one looking down at the top edge to clearly show the tooth sockets and the width of the bone.