Innominate Bone (Fragment)
Flat bone; part of the appendicular skeleton (limb support system)
Also known as: Hip bone, Pelvic bone, or Os Coxae
Classification
Flat bone; part of the appendicular skeleton (limb support system)
Dimensions
In large mammals, this is typically one of the most substantial and robust bones. It is characterized by broad, flat blades that narrow into thick, rounded bars around the central cup-like socket.
Key Features
This fragment shows the characteristic 'cellular' or honeycombed internal texture common in the thicker parts of the pelvis. Look for the 'acetabulum,' which is a deep, circular cup that holds the head of the thigh bone. The bone usually transitions from a thin, paper-like wing to a very dense, heavy bridge. The irregular, curving edges and the way the bone twists like a propeller are excellent identification cues.
Similar Bones
It can be confused with the shoulder blade (scapula). However, the hip bone is generally thicker and more robust, with a deep, hollow cup for a joint, whereas the shoulder blade is flatter, thinner, and has a much shallower, oval-shaped socket.
Across Species
Across the animal kingdom, the hip bone's shape reflects how a creature moves. In many four-legged mammals like deer or cattle, the flat blades are upright and elongated to support powerful leg muscles for running. In birds, the hips are fused into a rigid structure called a synsacrum to provide stability during flight. In aquatic mammals like whales, the hip bones have shrunk into tiny, unattached remnants deep within the body, as they no longer need to support the weight of limbs on land.
Evolutionary History
The hip bone evolved from simple plates in the belly of early fish-like ancestors into a complex three-part structure as vertebrates moved onto land. This change allowed limbs to be tucked under the body rather than splayed to the sides, enabling more efficient walking and running. Over millions of years, the bone broadened to provide more surface area for the massive muscles required for terrestrial locomotion.
Photography Tips
To identify a fragment like this, place a common object like a coin or a ruler next to it for size reference. Take one photo looking directly down at the flat surface and another from the side to show the thickness and 'honeycomb' internal structure. Use a plain background and natural light to highlight the subtle ridges where muscles once attached.