Humerus
Pneumatic Long Bone; part of the limb (appendicular) skeleton.
Also known as: Upper Wing Bone (in birds), Upper Arm Bone (in mammals)
Classification
Pneumatic Long Bone; part of the limb (appendicular) skeleton.
Dimensions
This is a long, slender bone with a straight, thin shaft and flared ends. Its length is usually several times its width, typical of animals that require reach or leverage in their limbs.
Key Features
The most defining feature of a bird's upper wing bone is the large, hollowed-out area or 'pocket' found on the underside of the rounded top end. This top area is broad and flattened to meet the shoulder, while the shaft is remarkably straight. The bottom end is much smaller and split into two distinct rounded knobs where it connects to the lower wing.
Similar Bones
This bone is most commonly confused with the femur (thigh bone). To tell them apart, look at the top end: the femur almost always has a distinct, ball-like 'neck' that sticks out to the side, whereas this wing bone is more flattened and flared at the top without a separate protruding neck. Additionally, bird wing bones usually feel much lighter in the hand than mammal limb bones of a similar size.
Across Species
In birds, this bone is often 'pneumatic,' meaning it is hollow and filled with air sacs to keep the skeleton light for flight. Large soaring birds like pelicans or albatrosses have extremely long, thin wing bones to catch wind currents. In contrast, flightless birds like penguins have flattened, solid wing bones that act like heavy paddles for swimming. In mammals like dogs or deer, this same bone is much thicker and denser to support the weight of the body while walking.
Evolutionary History
This bone can be traced back over 300 million years to the sturdy fins of ancient lobe-finned fish. As vertebrates moved onto land, these fins evolved into the powerful limbs of amphibians and reptiles. In the lineage leading to birds, the bone became increasingly lightweight and adapted for life in the air, while in terrestrial mammals, it developed ridges and grooves to anchor large muscles used for running and digging.
Photography Tips
Lay the bone flat on a plain, non-reflective surface. Take one photo from directly above to show the full length and curves. Take a second, close-up photo of the wide top end, making sure the deep pocket or hollow is clearly visible, as this is the best cue for identification. Including a common object like a coin or a ruler in the frame helps show the true size.