The StW 573 Little Foot Fossil Should Not Be Attributed to Australopithecus prometheus

Objectives: To test the hypothesis that the StW 573 (Little Foot) fossil specimen should be attributed taxonomically to Australopithecus prometheus. Materials and Methods: We adopt the methods of classic morphology by comparing StW 573 to the type specimen of A. prometheus (MLD 1) and other consensus members of Australopithecus africanus. We utilize qualitative anatomical descriptions and comparisons, supplemented with the examination of selected relevant quantitative measurements. Results: We find that the morphology preserved by StW 573 does not support assigning that specimen to A. prometheus because it does not share a unique suite of primitive and derived traits in common with the A. prometheus type specimen, MLD 1. Specifically, StW 573 differs from MLD 1 in having a more pronounced external occipital protuberance, a sagittal crest at lambda, an asterionic notch, a long nuchal plane, and a smaller cranial capacity. Regarding these same areas of anatomy, MLD 1 more closely resembles Sts 5, and MLD 37/38, consensus members of A. africanus. Discussion: A. prometheus should remain a junior synonym for A. africanus based on the demonstrated morphological similarities between MLD 1 and the broader A. africanus sample. Conversely, while StW 573 cannot be attributed to A. prometheus, the results of this study indicate that it also differs in meaningful ways from specimens conventionally attributed to A. africanus.