Revisiting the developmental stage and age-at-death of the "Mrs. Ples" (Sts 5) and Sts 14 specimens from Sterkfontein (South Africa): do they belong to the same individual?

During the 1947 fieldwork season, Member 4 (2-3 My) of the South African Sterkfontein site yielded two important Australopithecus africanus fossils: a cranium popularly nicknamed "Mrs. Ples" (Sts 5), and a partial skeleton (Sts 14). Previous reports have proposed that Sts 5 was a nonfully grown adolescent individual (Thackeray et al., S Afr J Sci 2002a;98:21-22), and that Sts 14 was a sub-adult specimen (according to various signs of immaturity in the skeleton) (Berge and Gommery, C R Acad Sci Paris, Sciences de la terre et des planètes 1999;329:227-232; Häusler and Berger, J Hum Evol, 2001;40:411-417; Thackeray et al., S Afr J Sci, 2002b;98:211-212). It was subsequently proposed that these fossils actually belonged to the same individual (Thackeray et al., S Afr J Sci, 2002b;98:211-212), a proposition supported by their spatial positions within the site. The present work attempts to revise these different assertions. The results obtained: (i) show that the Sts 5 fossil represents a fully grown adult cranium; (ii) provide new evidence of immaturity in the Sts 14 skeletal elements (sustaining the proposed young adult age of this specimen), and (iii) suggest that although the revised ages-at-death for these fossils are partially compatible, there is no evidence to support the idea that they represent a single individual. Finally, the encephalization quotient associated with a hypothetical union of Sts 5 and Sts 14 (calculated using data from both specimens) lies between the upper and lower limits of the currently estimated range for this species and H. habilis, respectively.