Australopithecus afarensis had a human-like foot in the sense that its great toe was aligned with the rest of the toes, adducted, but it did not have arched feet (Heile-Selassie, 2012), which is what makes the human foot stiff, favourable for walking but not at all for climbing trees and an arboreal life style. In the same time period, Paranthropus deyiremeda, a separate lineage that split from Australopithecus close to the Pan-Homo split, had developed arched feet (Heile-Selassie, 2012), an adaptation that may have later been transferred to Australopithecus by introgression during a population bottleneck, rather than through convergent evolution.
What sort of niche does a paddle-like, soft and flexible foot, fill? Not walking, not running, not climbing: swimming.
