Sternum
Flat bone, part of the core axial skeleton in birds
Also known as: Breastbone or Keel bone
Classification
Flat bone, part of the core axial skeleton in birds
Dimensions
Varies widely by species, generally elongated and shield-like with a prominent central ridge running along the bottom.
Key Features
Characterized by a long, flat plate-like base topped with a prominent, curved vertical blade running down the middle. Tiny natural holes or notches may appear along the edges depending on the species.
Similar Bones
Can be mistaken for pelvic bones or shoulder blades due to the flat surfaces, but the presence of the central knife-like ridge immediately gives away its identity as a bird breastbone.
Across Species
In flying birds, this bone features an exaggerated, knife-like vertical ridge called a keel, which anchors the massive flight muscles. In flightless birds like ostriches, the bone is flat like a raft because powerful flight muscles are unnecessary. In mammals, the breastbone is segmented and lacks the giant vertical ridge.
Evolutionary History
The avian breastbone evolved from simpler reptilian chest plates, transforming dramatically as dinosaurs took to the air. The development of the deep keel allowed early birds to anchor the powerful musculature required for powered, flapping flight.
Photography Tips
Place the bone on a solid, contrasting background. Take one photo from the side to show the height of the central ridge curve, and another from the top looking down at the flat plate. Include a coin or ruler for scale.