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. Copyright (c) 2008 Wiley-Liss, Inc.