Final answer:
Australopithecus afarensis became bipedal due to evidence from footprints, pelvic shape, and other anatomical features.
Step-by-step explanation:
The belief that Australopithecus afarensis became bipedal is supported by several lines of evidence. One piece of evidence is the discovery of footprints made by early hominins at the site of Laetoli in East Africa. These footprints show a striding gait similar to modern humans, indicating bipedal locomotion. Additionally, the morphology of A. afarensis, such as their pelvic shape, suggests bipedalism. Other anatomical features, like the position of the foramen magnum and the angle of the femoral head and neck, also support the hypothesis of bipedalism in A. afarensis.