CHIMPANZEE VARIATION FACILITATES THE INTERPRETATION OF THE INCISIVE SUTURE CLOSURE IN SOUTH-AFRICAN PLIOPLEISTOCENE HOMINIDS

For a better understanding of early hominid growth patterns, we need t o compare skeletal maturation among humans and chimpanzees. This study provides new data on variation of the incisive suture closure in exta nt species to facilitate the understanding of growth patterns among So uth African Plio-Pleistocene hominids. The complete anterior closure o f the incisive suture occurs early during human life, mostly before bi rth. In contrast, in chimpanzees a complete anterior closure occurs mo stly after the eruption of either the first permanent molars (pygmy ch impanzees) or the third molars (common chimpanzees). The first aim of this study is to test whether the patterns of closure of both the ante rior and palatal components of the incisive suture in chimpanzees accu rately mirror their polytypism by investigating 720 museum specimens o f known geographical origin. Then we use the data gleaned from the inc isive suture closure in chimpanzees to determine whether there are dif ferent growth patterns among South African Plio-Pleistocene hominids a nd to interpret them. Results about the pattern of incisive suture clo sure are consistent with the differences among chimpanzees as revealed by molecular data. Thus, the variation in chimpanzee patterns of inci sive suture closure facilitates the interpretation of morphology in So uth African fossil hominids. In Australopithecus (Paranthropus) robust us as compared to Australopithecus africanus, the complete anterior cl osure and, probably, the complete palatal closure of the incisive sutu re occurs during early life in the same way as they occur in humans. M oreover, the closure pattern observed on Stw 53, a supposed early Homo from Sterkfontein Member 5, is similar to that seen in A. africanus a nd in chimpanzees. Thus, with respect to the anterior component of the incisive suture, A. africanus and Stw 53 retain the primitive feature for which A. (P.) robustus and Home share the derived character state . Finally, it is worth noting that the Taung child does not show the r obust condition. (C) 1998 Wiley-Liss, Inc.