Femur (Specimen Fragment)
Long Bone, Limb Skeleton (Appendicular)
Also known as: Thigh Bone, Upper Leg Bone
Classification
Long Bone, Limb Skeleton (Appendicular)
Dimensions
In mammals, the femur is typically the longest and strongest bone. Even in fragments, it is characterized by massive, rounded ends and a thick, dense outer wall surrounding a hollow center.
Key Features
Identifying marks include a smooth, ball-shaped 'head' that fits into the hip socket and a distinctive bony protrusion near it for muscle attachment. The fragment shown highlights the thick, ivory-like density of the outer layer and the rounded, knuckle-like shape at the joint area.
Similar Bones
The humerus (upper arm bone) is often confused with the femur. Look for a more perfectly spherical 'head' on the femur, whereas the humerus usually has a more flattened or oval-shaped top and a more complex spool-like shape at the bottom joint.
Across Species
Across the animal kingdom, the femur adapts to suit locomotion. In heavy mammals like elephants, it is pillar-like to support weight; in hopping creatures like rabbits, it is long and slender for leverage. Bird femurs are often hollow and light, while the fossil record shows the femur of whales becoming small and buried deep within the body as they moved from land to sea.
Evolutionary History
The femur is a ancient structure dating back to the first vertebrates that walked on land. It evolved from the lobe-fins of ancient fish, eventually rotating underneath the body in mammals to allow for efficient upright walking and running, rather than the sprawling gait seen in early reptiles.
Photography Tips
To help with identification, place a standard ruler or coin next to the specimen for scale. Take photos from several angles: one looking straight at the smooth joint surface, one of the side profile, and a close-up of the textured interior if the bone is broken.