Volume 23 1980

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    Palaeontologia africana Volume 23
    (Bernard Price Institute for Palaeontological Research, 1980)
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    The Sterkfontein Valley australopithecine succession
    (Bernard Price Institute for Palaeontological Research, 1980) Vrba, E. S.
    If we knew the kinds and relative frequencies of animal species belonging to a natural living community, we would be able to predict the supporting environment with some accuracy. Unfortunately for the palaeoecologist the equivalent parameters of a fossil assemblage usually differ substantially from those of the ancient living parent community. This distortion results from the action of a number of taphonomic factors during the passage of remains "from the biosphere to the lithosphere". The major steps of palaeoenvironmental reconstruction from fossils follow a circuitous route of erecting hypotheses upon hypotheses: 1. Analyses of taxonomy and relative frequency. 2. Recognition of environmental indicators (El): Which fossil groups are environmentally specialized (i.e. good Els); and precisely what kind of environments do they indicate? (estimated from modern analogy). 3. Recognition of taphonomic biases: Have the proportions of Els in the original community been distorted by preferential inclusion and survival in the assemblage? Such bias or distortion may be caused by many factors, for example seasonality and duration of deposition, geographic area sampled, mode of death, transport and accumulation, species death rate, and so forth. 4. Estimation of El proportions in the original community by correcting where necessary for taphonomic biases. 5. Interpretation of taxonomic and morphologic change: Let us assume that estimates of original EI proportions, resulting from steps 1-4, can be seen to change significantly in chronologically successive strata in one area like the Sterkfontein Valley. Must such morphologic/ taxonomic change necessarily imply a change in the ecosystem, or may it imply no more than the passage of time? A particular palaeoenvironmental study on fossil assemblages from Sterkfontein, Swartkrans and Kromdraai is followed through steps 1-5 to its conclusion.
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    Dating possibilities for the South African hominid sites
    (Bernard Price Institute for Palaeontological Research, 1980) Vogel, J. C.
    A brief description is given of dating methods which may in future prove to be applicable to the calcified ossiferous cave deposits of the early hominid sites in the Transvaal. Potentially the techniques based on amino acid racemisation, uranium series disequilibrium and radiation damage could provide dates for at least the upper members of the cave formations. The results would, however, have. to be calibrated in the younger time-range by radiocarbon dating of parallel samples.
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    Sedimentological characteristics of the "red muds" at Makapansgat Limeworks
    (Bernard Price Institute for Palaeontological Research, 1980) Turner, Brian R.
    The "red muds" which occur at Rodent Corner along the west face of the exit quarry at Makapansgat limeworks have been divided into two sedimentary facies according to lithology, sedimentary properties and biological content: (1) coarse sandstone; and (2) siltstone and fine-sandstone. These two facies form a depositional couplet or sedimentary motif that occurs throughout the deposits and can be used as a basis for interpretation of the conditions of deposition. The coarse sandstone facies consists of thin lenticular beds which contain occasional elongate bone fragments showing a pronounced sedimentary fabric. This facies was probably deposited by flowing water, but, because of its coarse grain size, scale and low granulometric contrast, traction current structures such as cross-bedding and ripple cross-lamination were not developed. The angular character of the individual grains implies a short distance of transport and local derivation of the facies. The siltstone and fine sandstone facies is red and calcareous and contains sporadically distributed coarse sand grains. It is generally thicker and laterally more persistent than the coarse sandstone facies and capped by a mudcracked surface. The general characteristics of this facies are consistent with deposition in slow-moving or standing water from quiet suspension sedimentation. Shallowing of the water, related to changes in level of the water table, led to exposure of the depositional surface and the development of mudcracks. A variation of this facies pattern occurs in the middle of the succession where two limestone layers were deposited, the upper one intimately associated with local concentrations of cave pearls which originated from the lime-rich surface waters in locally agitated pools by concentration and precipitation of carbonate about a central nucleus. The facies couplet is interpreted in terms of storm and fair weather processes and compared with modern analogues found on shallow marine shelves, alluvial plains and in lakes. The coarse sandstone facies is attributed to storms and heavy rainfall outside the cave washing in coarse sandy detritus and raising the level of the water table. Between storm episodes quiet suspension sedimentation occurred accompanied by a gradual shallowing of the water table. Thus the coarse sandstone facies provides clues to storm periodicities and rainfall and suggests a rather wet climatic regime at this time. The red muds at Rodent Corner differ from those near the "Ancient Entrance" in that they contain coarse sandy interbeds, implying that the two deposits were separated from one another, possibly by a floor high, and that the opening into the cave at this time was small and probably located close to Rodent Corner.
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    "Australopithecus afarensis" and A. Africanus: Critique and an alternative hypothesis
    (Bernard Price Institute for Palaeontological Research, 1980) Tobias, Phillip V.
    During the seventies, a succession of East African discoveries has been claimed to represent the "true" ancestral line of modern man, thus relegating A. africanus, and especially its Transvaal subspecies, to a subordinate role in hominid phylogeny. The latest such attempt has been the claim of Johanson and his co-workers that the 3, 7-2,6 My-old hominids of Laetoli in Tanzania and of Hadar in Ethiopia represent a new species, "A. afarensis", which led to H. habilis, whilst A. africanus represents early stages in a specialized side-branch leading to A. robustus and A. boisei. A critique of the diagnostic criteria of "A. afarensis" reveals that on the available evidence, the Laetoli and Hadar fossils cannot be distinguished at specific level from A. africanus transvaalensis. Furthermore, it is by no means clear that the pooling for statistical and comparative purposes of the Hadar and Laetoli fossils is justified. Hominids from the two sites are separated by about 800 000 years and about 1 600 km as well as by morphometric differences. As an alternative hypothesis, it is proposed that the Laetoli and Hadar hominids belong to the same lineage as that represented by the hominids of Makapansgat Members 3 and 4 and of Sterkfontein Member 4. Moreover, it is hypothesized that the Laetoli and Hadar hominids cannot be separated morphologically from A. africanus and that they represent two new subspecies of that species. Since "A. afarensis" is tied to a Laetoli specimen as holotype, only the Laetoli specimens should be designated A. africanus afarensis (though A. africanus tanzaniensis suggested by the author in 1978 would have been a more appropriate nomen) and the Hadar fossils A. africanus aethiopicus. These newest East African discoveries afford strong confirmation of the hypothesis that A. africanus is the common ancestor of the two later hominid lineages, A. robustuslboisei and Homo, leading from H. habilis through H. erectus to H. sapiens.