Final answer:
Orrorin tugenensis is the early hominin ancestor that has shown the most evidence for bipedalism, due to its anatomical traits that suggest bipedal locomotion.
Step-by-step explanation:
Of the early hominin ancestors mentioned, Orrorin tugenensis has shown the most evidence for bipedalism. Orrorin was discovered in Kenya and dated to around 6 million years ago. Its anatomical traits, such as the large femoral head and dental characteristics, suggest a strong potential for bipedal locomotion. On the other hand, Ardipithecus ramidus, found in Ethiopia and dated to about 4.4 million years ago, also showed bipedal traits. Yet, the evidence for Ardipithecus includes adaptive features for life both on the ground and in trees. In contrast, Homo erectus, much later around 2.8 million years ago, demonstrates an almost human-like efficiency in bipedal locomotion with several skeletal adaptations.