In his description of hominid specimens from Olduvai Gorge in Tanzania, Tobias (1967, 1991) includes data on several maxillary features which he used for purposes of taxonomic distinctions. Here we consider two of these, focusing on the corpus maxillaris and its associated sinus maxillaris:

1. Minimum orbito-alveolar height as defined by Martin (1928, measurement 48-3)

2. Infra-orbital foramen vertical position indices, based on measurements of the orbito-foraminal height, expressed as a percentage of the minimum orbito-alveolar height.

In this study we re-examine data obtained from East African hominids, compared to new data that we have obtained from South African specimens from Swartkrans and Kromdraai, attributed to Australopithecus (Paranthropus) robustus. We also examine SK 847, now generally regarded as a species of early Homo (Clarke, 1994; Clarke et al, 1970; Brain 1981; Grine et al, 1993), although at least part of it had been considered to represent A. robustus (Mann, 1970). The main purpose of this study is to question again the possibility that SK 847 is a female individual of a species also represented by crania from Swartkrans that have previously been regarded as A. robustus.

Tobias (1991, 169-170) considered that there was a clear-cut morphological trend in the absolute values of the minimum orbito-alveolar height, a variable which he considered important for distinguishing early Homo from ‘robust’ australopithecines. However, in this study, we have obtained a value of 52.1 (+/- 0.1 mm based on six measurements) for this variable in SK 847 generally attributed to early Homo, and this measurement is not significantly different (p=0.05) from the corresponding mean value of 56.1 (+/- 4.4) based on measurements from six specimens attributed to A. robustus, including TM 1517 (from Kromdraai) and SK 12, SK 46, SK 48, SK 52, SK 83 (from Swartkrans).

Our value of only 52.1 mm for the minimum orbito-alveolar height in SK 847 is not only within the range of variability of corresponding values for this variable in six specimens of A. robustus (ranging from 49.5 - 61.5 mm), but it is also near the low end of the spectrum of values. This is consistent with the possibility that SK 847 may be a female of a species represented by other specimens that have been attributed to A. robustus (Thackeray, 1995).

A value of 75.1 mm has been obtained for the minimum orbito-alveolar height in OH 5, the type specimen of Australopithecus boisei, considered to be a male of this species (Tobias, 1967). A value of 61.1 mm has been obtained for KNM-ER 406, another male ‘robust’ hominid of the same species. By contrast, the minimum orbito-alveolar height of another specimen of A. boisei, KNM-ER 732, is only 47.5 mm, and this specimen is believed to be a female. The variability of minimum orbito-alveolar height in male and female specimens of the East African ‘robust’ australopithecine corresponds closely to that which is found for the same variable in South African specimens TM 1517, SK 12, SK 46, SK 48, SK 52, SK 83 and SK 847, with SK 847 at the lower end of the range of variability for the South African hominids..

In his discussion of specimens of early Homo from Olduvai Gorge, Tobias (1991, 170) discussed infra-orbital foramen vertical position indices based on measurements of the orbito-foraminal height, expressed as a percentage of the minimum orbito-alveolar height. Here we use this index to make comparisons between measurements obtained from SK 847, compared to corresponding values for specimens attributed to A. robustus. In the case of SK 847 it was necessary to obtain minimum estimates on account of damage to the specimen, but we believe that they are close to those expected in an undamaged condition. The measurements were used to establish that in SK 847 the infra-orbital foramen vertical position index of 27.2 (+/- 0.2, based on six sets of measurements) is within the range of variation between 26.9 (minimum) and 44.0 (maximum) reported for A. robustus by Tobias (1991, 170), and again SK 847 is near the lower end of the spectrum of values obtained for A. robustus.

We conclude that the data presented above are consistent with the possibility that SK 847 is a female of a species represented by other Swartkrans specimens that have been attributed to A. robustus. We recommend that further studies be undertaken on the variables we have studied. In particular we recommend the use of CT scanning to extend our analysis of the minimum orbito-alveolar height and infra-orbital foramen vertical position indices in South African and East African hominids.

Acknowledgments

P.V. Tobias kindly discussed the topics which we have re-examined in this study, which has

been supported by funds from the National Research Foundation (South Africa), and a grant from the French Embassy in Pretoria (Cultural Services). We are particularly grateful to B. Senut, M. Pickford, Y. Coppens, J. de Mones, and T. d’Albis for being instrumental in facilitating collaboration between palaeontologists from France and South Africa. We thank B. Vandermeersch for his encouragement and support.

References

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