Sex at Sterkfontein: ‘Mrs. Ples’ is still an adult female

The important question of whether the Australopithecus africanus hypodigm is taxonomically heterogeneous revolves largely around the interpretation of the morphological variation exhibited by the fossils from Sterkfontein. The sex assignment of these specimens is a critical component in the evaluation of their morphological variability. The Sts 5 cranium is pivotal in this regard because it is the most complete and undistorted specimen attributed to A. africanus. Although it has traditionally been regarded as an adult female, this view has been challenged. In particular, it has been argued recently that Sts 5 is a juvenile and that this, together with alveolar bone loss that has supposedly reduced the size of the canine socket, has led to its misinterpretation as a female. Virtual reconstruction of the M3 roots (and/or alveoli) contradicts arguments that these teeth were erupting at the time of death. Regardless, canine emergence and root completion are well ahead of M3 development in juvenile australopiths from Sterkfontein. Thus, even if the M3 root of Sts 5 was incomplete, its canine root would have been fully formed. Measurements of palate depth indicate that the alveolar margins of Sts 5 have not suffered from much (if any) bone loss in the region of the C/P3; any additional bone would result in a palate of truly exceptional depth. Therefore, the dimensions of the canine alveolus of Sts 5 can be regarded as proxies for those of the canine root. The canine root of Sts 5 is among the smallest recorded for any Sterkfontein australopith, which provides strong support for Robert Broom's initial attribution of sex to this specimen. There is no evidence to contradict the assertion that ‘Mrs. Ples’ is an adult female.