Australopithecus were "water-adapted apes", swimming apes. They had evolved a paddle-like foot with an adducted great toe by the mid Pliocene, which is inherited by humans today, but they lacked the arched foot of extant humans that makes the foot stiff, an adaptation for walking and running. Their foot was paddle-like, soft and flexible, not adapted for walking, not for climbing, but for swimming.
In the same time period, the Paranthropus lineage had evolved stiffened feet. (Haile-Selassie, 2012; Nygren, 2018) The Australopithecus and Paranthropus lineages each had unique derived features, while both of those features are found in Homo. The craniodental features of Paranthropus in the mid Pliocene also differ from Australopithecus (Haile-Selassie, 2015; Nygren, 2018), tough are similar to Homo .