Which early hominin is characterized as not fully bipedal?

The early hominin Ardipithecus is characterized as not fully bipedal due to its anatomical features which reflect a mix of adaptations for both climbing and upright walking. Fossil evidence suggests that while Ardipithecus had some traits associated with bipedalism, such as a more adapted pelvis and position of the foramen magnum, it also retained features suitable for grasping and climbing in trees, indicating it was still somewhat arboreal in behavior. This blend of traits demonstrates that Ardipithecus was evolving towards bipedal locomotion but had not fully transitioned to a completely upright gait.

In contrast, other hominins such as Australopithecus, Homo habilis, and Paranthropus exhibit more pronounced characteristics of bipedalism and show adaptations that suggest they were primarily terrestrial. Australopithecus, for instance, is known for its fully bipedal structure, while Homo habilis and Paranthropus also display significant adaptations for walking upright, making Ardipithecus stand out as the least fully bipedal among the options.