Femur (fragment)
Long Bone fragment, part of the appendicular (limb) skeleton
Also known as: Thigh Bone
Classification
Long Bone fragment, part of the appendicular (limb) skeleton
Dimensions
In mammals, this is typically the longest and heaviest bone. In large livestock like cattle or horses, the central shaft is thick-walled and roughly cylindrical, usually ranging from 8 to 20 inches in total length depending on the species.
Key Features
The most striking feature of a large mammal thigh bone is the thick outer wall of compact bone surrounding a large central hollow, which originally housed marrow. When found as a fragment, look for the 'D-shaped' or round cross-section and the presence of rough, stringy textures on the surface where muscles once anchored.
Similar Bones
The humerus (upper arm bone) is the most common look-alike. You can distinguish them by shape: the thigh bone shaft is typically more perfectly round or oval in the middle, while the upper arm bone often has a distinct spiral-like ridge wrapping around the center for shoulder muscle attachment.
Across Species
The thigh bone varies dramatically across the animal kingdom. While most mammals have a thick, marrow-filled shaft to support body weight, birds have hollow (pneumatized) thigh bones to stay light for flight. Marine mammals like whales have highly shortened and thickened thigh bones, as they no longer need to walk on land.
Evolutionary History
This bone appeared approximately 360 million years ago as lobe-finned fish transitioned into the first four-legged land animals (tetrapods). Over millions of years, it evolved from a flattened plate that jutted out to the side into a vertical column positioned directly under the body, allowing for more efficient running and walking in modern mammals.
Photography Tips
To identify fragments, photograph the bone from several angles. Always include a view of the broken end to show the thickness of the bone wall and the cavity inside. Place a common object like a coin or ruler next to the piece to provide a clear sense of size.