Sex at Sterkfontein: ‘Mrs. Ples’ is still an adult female Frederick E. Grine a, b, * , Gerhard W. Weber c , J. Michael Plavcan d , Stefano Benazzi c a Department of Anthropology, Stony Brook University, Stony Brook, NY 11794-4364, USA b Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY 11794-8081, USA c Department of Anthropology, University of Vienna, Althanstraße 14, Vienna 1090, Austria d Department of Anthropology, University of Arkansas, Fayetteville, AR 72701-1201, USA article info Article history: Received 19 October 2011 Accepted 31 January 2012 Available online 27 March 2012 Keywords: Sexual dimorphism Canine root size Palate depth Dental development Computed tomography Australopithecus africanus abstract 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 M 3 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 M 3 development in juvenile australopiths from Sterkfontein. Thus, even if the M 3 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/P 3 ; 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. Ó 2012 Elsevier Ltd. All rights reserved. Introduction The species Australopithecus africanus is conventionally held to be represented by fossils from Taung, Sterkfontein (especially Member 4) and Makapansgat (Tobias, 1978; White et al., 1981; Rak, 1983; Strait et al.,1997; Wood and Richmond, 2000; MacLatchy et al., 2010). This taxon is one of the least stable in phylogenetic analyses (cf. Skelton et al., 1986; Chamberlain and Wood, 1987; Skelton and McHenry, 1992; Strait et al., 1997; Kimbel et al., 2004; Strait and Grine, 2004), and its instability is almost certainly owing to the fact that it is variable in so many craniodental characters (Strait et al., 1997). The question of whether this variation is attributable to taxonomic heterogeneity within the hypodigm has been a point of prolonged discussion (e.g., Clarke, 1985, 1988, 1994, 2008; Kimbel and White, 1988; Lockwood, 1997; Lockwood and Tobias, 2002). The sex assignment of the Sterkfontein specimens is critical to evaluating the taxonomic significance of this variation (Kimbel and White, 1988; Lockwood, 1997 , 1999; Lockwood and Tobias, 2002). For example, Kimbel and White observed that greater facial prognathism and robusticity are expected for males in sexually dimorphic hominids. Because they regarded the comparatively orthognathic Sts 71 cranium to be male on the basis of facial robusticity and postcanine tooth size, they opined that “if Sts 5 is a female, as is commonly thought, then the differences in facial prognathism between these specimens is opposite that which characterizes the sexes in great apes” (1988: 185). Although Broom (1950: 2) had argued “the case of the splitter of the South African ape-men,” recognizing three species to accom- modate the fossils from Taung, Sterkfontein and Makapansgat, he nonetheless did not recognize any taxonomic distinction within either the Sterkfontein or Makapansgat assemblages. Although some of the Sterkfontein crania were seen to differ “very consid- erably” from one another (Broom and Robinson, 1950: 26), sexual dimorphism was believed to account for at least some of this variation. Specimens such as TM 1511 1 , TM 1512, Sts 5, Sts 17, Sts 71 * Corresponding author. E-mail address: frederick.grine@stonybrook.edu (F.E. Grine). 1 Broom (1946) initially regarded TM 1511 as being not improbably a young male, but following the discovery of an “excellent upper canine” of a male (Sts 3) (Broom and Robinson, 1950: 57) he subsequentlycame to view TM 1511 as female owing to the size of its canine alveolus (Broom and Robinson, 1950). Although Sts 3 was interpreted as a maxillary canine by Broom and Robinson (1950: Fig. 14), Robinson (1956) later identified it as a mandibular tooth. Contents lists available at SciVerse ScienceDirect Journal of Human Evolution journal homepage: www.elsevier.com/locate/jhevol 0047-2484/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jhevol.2012.01.010 Journal of Human Evolution 62 (2012) 593e604