Dentary
Irregular bone, Flat bone, part of the facial skeleton (core/axial)
Also known as: Lower Jawbone, Fish Mandible, Tooth-bearer
Classification
Irregular bone, Flat bone, part of the facial skeleton (core/axial)
Dimensions
Typically longer than it is tall, providing a lever-like structure. In many bony fish, this bone can range from a few millimeters in minnows to several feet in giant predatory species like marlin.
Key Features
Look for a clear row of small peaks or sockets along one edge where teeth were once seated. It often has a distinct 'V' or 'L' shape when viewed from the side, with a thin, plate-like body and a sturdier, thickened edge that supported the bite. The bone is often translucent or very light in fish specimens.
Similar Bones
The premaxilla or maxilla (upper jaw bones) are the most similar. You can distinguish the dentary by its characteristic upward curve toward the front and the way it hinges at the back. It may also be confused with a broken piece of a pectoral fin spine, but the presence of tooth sockets is a dead giveaway for a jawbone.
Across Species
In fish, the dentary is the main tooth-bearing bone of the lower jaw, often featuring a serrated edge or distinct sockets. Unlike the single-bone mandible found in mammals, fish jaws are a complex puzzle of multiple interlocking bones. In predatory fish like pike, the dentary is elongated and needle-thin to snap shut quickly, while in bottom-feeders it may be shorter and thicker for crushing shells.
Evolutionary History
The dentary has undergone a massive transformation through deep time. In early jawed vertebrates, it was just one of many small bones in the lower jaw. Over millions of years, as vertebrates transitioned from water to land, the dentary became increasingly dominant. In mammals, it eventually became the only bone in the lower jaw, while the other smaller jaw bones moved into the ear to help with hearing.
Photography Tips
Place the bone on a flat, neutral background. Take one photo directly from the side to show the profile and tooth row, and another looking straight down at the biting surface. Including a coin or a ruler for scale is essential for identifying the specific type of fish.