LATERAL VIEW OF AUSTRALOPITHECUS-AFARENSIS - PRIMITIVE ASPECTS OF BIPEDAL POSITIONAL BEHAVIOR IN THE EARLIEST HOMINIDS

The pelvis of A1 288-1, when studied laterally, shows the following: (1) the promontory angle measures 70-degrees; (2) the anterior plane of Sl is perpendicular to the plane formed by the biauricular and biacetabular lines; (3) the plane formed by the biauricular and biacetabular lines on one hand, and the plane formed by the two anterior-superior iliac spines and the symphysion on the other hand, are parallel. When the biauricular-biacetabular plane is vertical (necssary requirement for erect posture), the anterior plane of Sl is horizontal and the sacral base makes a steep 70-degrees with the horizontal. In addition, if the vertebral spine is vertical (which is the concept of many anthropologists), lordosis, or the angle formed by the bases of L3 and S1 would have to be 70-degrees. Such concepts, i.e., the sacral base making a steep 70-degrees with the horizontal and a 70-degrees lordosis, are never seen in human erect posture, except under pathological conditions, and are barely compatible with proper erect posture and locomotion. Other possibilities have been proposed in the anthropological literature and are reviewed. The conclusion is that Lucy's erect posture is unlike that seen in modern humans and is still a mystery. Not enough fossil data are yet available to make a final judgement on the nature of her erect posture.