Dating the fossil record
These footprints are remarkably similar to those of modern humans in key details, including a forward-pointing big toe, relatively short lateral toes, and arched feet.
The main fossil sample of this species comes from is a mosaic of primitive features and evolutionary developments shared by later hominins.
Its skull is primitive in having a crest and a strongly projecting (prognathic) lower face.
The brain was about one-third the size of a modern human’s.
The oldest dates are approximately 3.3 mya for hominin specimens (perhaps appear to be smaller and the upper limbs larger.
Males weighed approximately 41 kg (90 pounds) and stood 138 cm (4 feet 6 inches) tall.
Whether it walked upright is not known because only a single skull, jaw fragments, and teeth have been found.
Bipedalism may have been established in the six-million-year-old is primitive in most if not all of its body except for femurs (thighbones) that appear to share traits of bipedalism with modern humans.
The case for its hominin status rests on the humanlike features of the femur.In 1947 a partial skeleton was unearthed that revealed the humanlike specializations for bipedalism now known to be characteristic of all australopiths.Almost all of the remains from Sterkfontein come from a deposit where there is a conspicuous absence of stone tools.In addition, the ankle and knee are specialized for upright walking.
Other skeletal features are very much like those of later hominins.
The dentition is also mostly primitive, with canines that shear against the lower premolars and a gap (diastema) between the upper incisors and canines.