The correct option is A Australopithecus
Ancestor of man who first stood erect was australopithecus. The various species of Australopithecus lived during the Pliocene (5.3 to 2.6 million years ago) and Pleistocene (2.6 million to 11,700 years ago) epochs. Like humans, they were bipedal and they had small brains. Hence, option A is correct.