Other features on Ar. ramidus’s skull that distinguish it include the placement of the foramen magnum on the underside and shortened basioccipital area (the raised part around the foramen magnum).
The brain case of Ar. ramidus is similar to a modern chimpanzee, around 300-350 cubic centimeters. This cavity is more ovular in chimpanzees, and more circular in Australopiths and humans.
The face lacks the prognathism found in modern African apes.
Note the difference in the following features between the 3d models below:
3D model homo sapiens (human) skull.
3D model Ar. ramidus skull.
3D model modern chimpanzee skull.
The location of the foreamen magnum towards the underside and thickened basioccipital area helps the spine support the weight of a the head while standing bipedally. These traits indicate upright posture in Ar. ramidus.
These features are called "derived traits"—features shared with other bipedal hominins and humans.
Up next: Other distinguishing features of Ar. ramidus.