(The dental arch of ranges from 380–530 cc (23.2–32.3 cubic inches), about one-third the size of that of a modern human.In addition, numerous anatomical details in the mandible and skull are indicative of an apelike ancestry and suppport the distinction of are commensurate with a terrestrial, striding, bipedal gait.Hominin fossils (which included an immature partial skeleton, jaws, and teeth) discovered at the northern Tanzanian site of Laetoli, dating to approximately 3.6 mya, are among the most ancient examples of individuals left a 24.4-metre- (80-foot-) long trail of their own footprints frozen in time.These footprints were made by an arched foot that possessed a forward-pointing great toe, a strong heel strike, and powerful toe-off (that is, where the toes leave the ground during a step)—all of which are hallmarks of human bipedalism. Another feature of the Bouri specimen was a crest running along the midline of the braincase, the sagittal crest.Perhaps the most famous specimen of (2.3–1.2 mya), which comprises three species of australopiths—collectively called the “robusts” because of their very large cheek teeth set in massive jaws.
The extremely large hands of the species suggest a lifestyle that included significant climbing and other activities among the trees.
The pelvis is a mix of ape and human traits; it appears to be broader, shorter, and narrower than an ape’s pelvis and reminiscent of a bipedal pelvis.
The foot is notably apelike with elongated toes and a fully divergent great toe for moving about in trees.
The case for its hominin status rests on the humanlike features of the femur.
According to its discoverers, features of the thighbone implying bipedalism include its overall proportions, the internal structure of the femoral neck (the column joining the ball-shaped head of the femur to the shaft of the bone), and a groove on the bone for a muscle used in upright walking (the obturator externus).