Bipedality and the pelvis

1 minute read

Humans are bipeds. The pelvis in humans has undergone radical changes in orientation and shape compared to other anthropoid primates. Many of these changes serve to adapt our muscle orientations to the requirements of upright stance and bipedal locomotion.

The most significant changes to the pelvis in humans compared to other apes are:

Ilium
The ilium (top portion of the innominate bone) in humans is shorter and broader. It curves around the trunk, whereas in apes it is flat against the back of the trunk.
Greater sciatic notch
This is very wide in apes, a function of their long, tall ilium. In humans, the notch is actually a notch.
Anterior inferior iliac spine
This feature is prominent in the hominin pelvis, absent or small in apes.
Sacrum
In humans, the sacrum is broad and short, in apes it is narrow and long, usually incorporating 6 or more sacral vertebral bodies.

What to do: This station has four pelvic bones from the species Australopithecus africanus, which existed around 2.6 million years ago in South Africa. Assess the anatomy of these bones in comparison to humans, chimpanzees and gorillas. Are these the pelvic bones of a biped? What features point to your conclusion?

In addition, the plaques at the front of the room have the near-complete skeleton of a fossil species, Oreopithecus bambolii, found in Tuscany and Sardinia around 8 million years ago. Look carefully at the pelvis of this skeleton. Does it resemble the living apes or humans? Does it look like Australopithecus?