Pelvis
Irregular bone; it serves as the foundational connection of the limb (appendicular) skeleton to the core (axial) skeleton.
Also known as: Hip bone, Pelvic girdle, Basin
Classification
Irregular bone; it serves as the foundational connection of the limb (appendicular) skeleton to the core (axial) skeleton.
Dimensions
In many mammals, this is a broad, sturdy structure. It is typically as wide as or wider than the shoulder girdle, forming a deep basin shape with large circular openings.
Key Features
It is easily recognized by its 'butterfly wing' appearance at the top and the large, hollow ring in the center. Look for the deep, cup-like sockets on the outer sides where the thigh bones attach, and a large, notch-like curve on the back inner edge that resembles a wide hook.
Similar Bones
The shoulder blade (scapula) is also a flat, winged bone, but it lacks the deep central hole and the heavy, circular sockets found in the pelvis. The pelvis is much heavier and more three-dimensional than the relatively flat shoulder blade.
Across Species
The pelvis varies wildly across the animal kingdom. In birds, it is often elongated and fused to the spine to provide a rigid frame for flight and landing. In whales, the pelvis has shrunk over millions of years into small, internal 'floating' bones that are no longer connected to the spine. Standing animals like bears and humans have broader, bowl-shaped bones to support the weight of internal organs against gravity, while four-legged runners like horses have longer, narrower pelvic structures for powerful muscle attachment.
Evolutionary History
The pelvis began as simple paired plates in early fish to support pelvic fins. As vertebrates moved onto land, these plates grew larger and fused with the spine to allow the hind limbs to push the body off the ground. Over deep time, the three separate bones of the hip—the upper blade, the sitting bone, and the front bone—fused into the solid basin we see in modern land-dwelling mammals.
Photography Tips
To get a clear identification, take one photo directly from the front to show the overall 'basin' shape and one from the side to capture the depth of the hip socket. Placing a recognizable object like a coin or a ruler next to it helps viewers understand the scale of the animal it came from.