Sternum fragment (likely avian)
Flat bone; part of the axial (core) skeleton
Also known as: Breastbone, Brisket bone, Keel bone
Classification
Flat bone; part of the axial (core) skeleton
Dimensions
Typically broad and thin, these bones vary widely in size from a few centimeters in small songbirds to several inches in large waterfowl or mammals. This specific piece is a flat, plate-like section characterized by its thinness relative to its surface area.
Key Features
Look for a thin, slightly curved plate that is very smooth on one side. This bone often features sharp, clean edges where other structures once attached. In birds, you will often find a high, thin wall (the keel) rising perpendicularly from the center line, resembling a blade or a fin.
Similar Bones
This could be confused with a shoulder blade (scapula) or a fragment of a skull. To tell them apart, check for symmetry and thickness; a shoulder blade is usually more triangular and has a thicker 'neck' at one end, while skull fragments often show tiny wavy lines (seams) where they once met other bones.
Across Species
In the animal kingdom, the breastbone is a master of adaptation. In flying birds, it develops a massive central ridge called a keel, which provides a huge surface area for flight muscle attachment—think of it as the hull of a ship. In contrast, flightless birds like ostriches have a flat, shield-like breastbone. Mammals like humans or dogs have a segmented, narrow breastbone that acts as a central anchor for the ribs, protecting the chest cavity.
Evolutionary History
The breastbone first appeared in early tetrapods as they transitioned from water to land, providing a necessary anchor for the front limbs to support body weight against gravity. Over millions of years, as some dinosaurs evolved into birds, the bone expanded and developed its signature ridge to accommodate the high power requirements of powered flight.
Photography Tips
To help with identification, photograph the bone from the side to show its thickness or the height of any ridges. Place a common object like a coin or a ruler next to it for scale, and try to use soft, natural light to highlight the subtle textures of the bone surface.