Orthograde posture

In order to walk upright with maximum efficiency, the skull, spine, pelvis, lower limbs, and feet all underwent evolutionary changes.

The first definitive evidence of habitual orthograde posture in human evolutionary lineage begins with Ardipithecus ramidus, dating between 5.2 and 5.8 million years ago.

The skeletal remains of this hominid exhibit a mosaic of morphological characteristics that would have been both adapted to an arboreal environment and walking upright terrestrially.

[4] The earliest evidence of a hominid exhibiting skeletal morphology capable of achieving orthograde posture dates to 9.5 million years ago, with the discovery of a Miocene ape, Dryopithecus in Can Llobateres, Spain.

However habitual bipedalism in australopiths meant though they nested among the branches in trees at night, they moved with orthograde posture such that their hands could also be used for gathering, feeding, weight transfer, or balance during the day.

Due to the more wooded barren savannahs of northern Africa, O. tugenensis and australopiths began to change, which is evident in morphological data accumulated from the remains of the different species.

Similarly in Australopithecus afarensis, the site of the space in the skull is even more human-like, inferiorly located such that the spinal cord would run perpendicularly to the ground.

[10] Relating this orientation to the encephalization of hominin of the time, the position foramen magnum assisted in balance and supported upright posture.

The femoral neck specifically, which connects the head of the femur to its primary shaft absorbs the force of impact when an upright biped assumes movement.

[14] In Orrorin tugenensis, the orientation of the head condyles of the broadened femur is wider and thicker in comparison to that of chimpanzees and other great apes.