is was thought, by reputable paleoanthropologists, to be the closest thing found that indicates we evolved from the ape branch.
How paleoanthropologists come to conclusions:
As in a modern humans skeleton, Lucy's bones are rife with evidence clearly pointing to bipedality. Her distal femur shows several traits unique to bipedality. The shaft is angled relative to the condyles (knee joint surfaces) which allows bipeds to balance on one leg at a time during locomotion. There is a prominent patellar lip to keep the patella (knee cap) from dislocating due to this angle. Her condyles are large, and are thus adapted to handling the added weight which results from shifting from four limbs to two. The pelvis exhibits a number of adaptations to bipedality. The entire structure has been remodeled to accommodate an upright stance and the need to balance the trunk on only one limb with each stride. The talus, in her ankle, shows evidence for a convergent big toe, sacrificing manipulative abilities for efficiency in bipedal locomotion. The vertebrae show evidence of the spinal curvatures necessitated by a permanent upright stance.