This illustration compares the crania of a female gorilla, Australopithecus africanus, and Homo sapiens. 

The dark area at the bottom of the skull is the foramen magnum, the hole through which the spinal column passes. It has a forward position in australopithecine skulls, a strong indication that they were bipedal. 

Note also that both the shape of the jaw and the teeth of australopithecines are very similar to those of modern humans. Australopithecines do not have the rectangular-shaped jaw or the large canine teeth of apes. 

This illustration is from "Humankind Emerging", edited by Bernard Campbell.