The Nature article about the new Australopithecus afarensis child (which is behind a subscription wall) gives more details. The endocranial volume is estimated because the head is not quite complete and it overlaps with both ape and human ranges. Other things:
• craniodental characteristics place it with A. afarensis
• post crania clearly indicates bipedality
• scapular border is more ape-like than human
This is a really interesting mix of traits and lends more credence to the idea that A. afarensis was a transitional form in the truest sense of the phrase.