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South African Journal of Science

versão On-line ISSN 1996-7489
versão impressa ISSN 0038-2353

S. Afr. j. sci. vol.108 no.1-2 Pretoria Jan. 2012

 

RESEARCH ARTICLE

 

Canteen Kopje: a new look at an old skull

 

 

Patricia SmithI; Robert NshimirimanaII; Frikkie de BeerII; David MorrisIII; Leon JacobsonIII,IV; Michael ChazanV; Liora K. HorwitzVI

IThe Laboratory of Biological Anthropology and Ancient DNA, Hadassah Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel
IIRadiation Science Department, Necsa, Pretoria, South Africa
IIIMcGregor Museum, Kimberley, South Africa
IVFaculty of Life Sciences, Cape Peninsula University of Technology, Cape Town, South Africa
VDepartment of Anthropology, University of Toronto, Toronto, Canada
VINatural History Collections, Faculty of Life Sciences, The Hebrew University, Jerusalem, Israel

Correspondence to

 

 


ABSTRACT

The Canteen Kopje (CK) skull was found by a diamond digger working the Vaal River gravels in 1929. It was hailed by Robert Broom as an exceptionally robust prehistoric individual that was ancestral to modern South African populations. Further exploration of the Vaal Gravels has confirmed the antiquity of the purported find locality, but the heavily restored CK cranium offers limited possibilities for morphometric re-examination or direct dating with which to test Broom's assertion. We used X-ray tomography to create a computerised 3D image that would provide optimal visualisation of the morphometry of the bony surfaces. The results showed that the CK cranium falls within the range of variation of Holocene Khoesan and lacks archaic features. We propose that it was probably a Late Stone Age intrusion into the Vaal Gravels or the overlying Hutton Sands.


 

 

Introduction

The Vaal River gravels first attracted attention in the late 19th century following the discovery of alluvial diamonds at Canteen Kopje (CK), then known as Klipdrift, situated about 36 km north-west of the city of Kimberley in the Northern Cape Province of South Africa (Figures 1 and 2). As diamond exploration continued, it became obvious that the Vaal Gravels were also an important archaeological locality yielding thousands of Acheulean artefacts.1,2,3 In 1913, a heavily mineralised fragmentary skeleton was found at Boskop near Johannesburg; the skeleton was attributed to an archaic South African population.4,5,6,7 The discovery a few years later of the Tuinplaas (or Springbok Flats) skeleton, associated with an extinct buffalo, was considered further proof of the presence of antecessors who differed from the extant populations of South Africa. Broom8 noted:

 

 

 

 

A few months ago, the discovery of the Springbok skull revealed to us the fact that many thousands of years ago there lived in South Africa a large-brained powerfully built race which was neither Bushman nor Bantu, and a race which in all essentials resembles the living Korannas [a Khoe group, remnants of whom lived along the Vaal and Riet Rivers9,10] so closely as to leave little doubt that the Korannas are the descendants.

Thus, the discovery in 1929 of human remains at the known Acheulean site of CK11 filled a vacant niche in an already well-constructed paradigm - one that influenced the thinking of physical anthropologists for many years.

The CK remains, comprising fragments of a human cranium, were discovered by a diamond digger named Kenneth Kemp and passed to J.G. van Alphen, 'magistrate, writer and fossil collector'12, who presented them to the McGregor Museum. The museum made the remains available to Robert Broom for examination. Broom11 published the first description of the skull in Nature, describing it as a 'fossilised human braincase recovered from an alluvial deposit of the Vaal River at Canteen Kopje near Barkly West.' Curiously, he also refers to 'some fragments of limb bones' found with the skull, but did not describe them and they are not mentioned in the museum's 1929 accession record (MMK 215: 'Skull [incomplete]').

According to Broom11, the CK human remains were heavily mineralised and discovered 'in a deep alluvial bank' (the museum's accession record suggests a depth of '8 ft'), but the exact find spot at the site is unknown. Seven decades later a 90-year-old digger, Mr Eddie Fortune,13 recalled that Mr Kemp's claim had been along the north-western edge of the diggings, east of the old Kimberley Road. This recollection would place the find spot of the CK skull downslope from the declared Provincial Heritage site zone of Canteen Kopje (Figure 2), possibly in a unit of the Younger Vaal Gravels closer to the river and chronologically more recent than the deposits within the declared heritage zone (Figure 3).14 Previous claims that the skull fragments came from the Younger Gravels beneath the Hutton Sands within the main Canteen Kopje site seem unlikely, given that there is no fossil bone preservation at this locality.15,16 The Younger Gravels at the main site are thought to be late Pliocene to Lower Pleistocene in age,3 corroborated by recent cosmogenic nuclide burial ages ranging from 1.89±0.19 Ma to 1.26±0.10 Ma for the Younger Gravels at Windsorton.17

 

Broom11 described the CK specimen as one of the largest and most robust he had ever examined. Broom identified the specimen as ancestral to modern South Africans, probably more recent than the Tuinplaas or Boskop skulls. The CK specimen was one of a number of crania discovered in South Africa in the first part of the 20th century that were grouped together because of their large cranial capacity and presumed antiquity into the so called 'Boskop' physical type. These crania were found throughout South Africa, some apparently associated with Middle Stone Age artefacts or in 'pre-Bushman' archaeological horizons.18,19,20,21,22,23,24,25 Accordingly, the crania played an important role in early discussions of the origin of the southern African Khoesan.26,27,28,29,30,31,32,33 New developments in the field have enabled researchers to date some of these specimens and re-examine their association with a specific archaeological horizon. At the same time, the application of advanced imaging and statistical techniques have provided better resolution and analysis of the size and shape of incomplete specimens, thus enabling their integration into the current human evolutionary record. This reclassification has been carried out for skeletal remains from Tuinplaas,34 Matjes River Rock Shelter,35 Hofmeyr,36 Peers Cave37 and other localities.38 Ranging in age from the late Pleistocene to the post-contact period, these specimens provide a chronological framework with which to evaluate the CK skull and assess the probability that it derives from the Vaal Gravels.

 

Materials and methods

Description of the Canteen Kopje skull

The CK cranium is incomplete. It comprises most of the occipital bone except for the basi-occiput, incomplete right and left temporal bones, part of the right mastoid process, most of the left parietal, but only fragments of the right parietal and left side of the frontal bone; about two-thirds of the lateral part of the supra-orbital margin and the orbital root of the zygomatic process are also present (Figure 4). The supra-orbital margin is broken inferiorly, which limits assessment of its size and shape. The left lateral portion of the frontal bone shows a pronounced, forward-projecting supra-orbital ridge, associated with a well-defined post-orbital sulcus. The supra-orbital ridge continues laterally as a pronounced supra-orbital shelf that forms the orbital root of the zygomatic process. The ascending portion of the lateral fragment of the frontal squama is low, but full and rounded. The superior temporal line is pronounced with a well-developed crest. The mastoid process is broad and is bounded medially by a deep digastric groove. Medial to this groove are two parallel, well-developed crests, with the medial one the most distinct.

 

 

Broom modelled the missing parts of the cranium in plaster of Paris: the face, the orbits, the glabella, the vault and most of the right side of the frontal and parietal bones, and the sphenoid (Figure 4). The resulting reconstruction shows a very long and low calvarium with projecting supra-orbital ridges and a short, broad face. Based on this reconstruction, Broom11 estimated cranial length (glabella to lambda) as 215 mm, maximum cranial breadth as 140 mm and basi-bregmatic height as 140 mm. It should be emphasised that three of the four landmarks used (glabella, bregma and basion) were missing and arbitrarily defined by Broom.

The occipital and parietal bones of CK are flattened superior-inferiorly, with lambda inferiorly located and there is a prominent occipital bun. How much of the flattening results from post-depositional compaction, and/or the reconstruction, is difficult to establish. Wells25 questioned the accuracy of the restoration, specifically the curvature of the parietal fragments and angulation of the occipital bone. He pointed out that the vault contour was somewhat lower and flatter in the restoration than in the original illustration given by Broom11, exaggerating the length of the skull. Even if the restoration exaggerated the length of the occipital chord, it would not have affected the length of the occipital arc, which is exceptionally long (measuring 120 mm from lambda to the most anterior portion of the incomplete basi-occiput).

A feature of the CK skull, which has not been previously described, is a well-defined circular depression located on the left side, some 44 mm posterior to the rim of the orbit and directly above the superior temporal line (Figures 4a-b and 5a). This lesion is approximately 2 cm in diameter with smooth, inwardly sloping margins and slightly raised edges (Figure 5a). The bone surrounding the lesion shows no cracks or breaks that would indicate that damage occurred around the time of death or post-mortem.

 


 

A depression of similar size and form is present on the frontal bone of at least one other cranium from the Northern Cape held in the McGregor collection - an adult female (catalogue number MMK 292) described in the McGregor museum's accessions catalogue as: 'Skull only, no lower jaw. Koffiefontein. 19/6/1946. [Presented by] W [illiam] Fowler'. It is one of about 57 burials excavated by Fowler in the environs of Koffiefontein that were attributed to the Late Stone Age Type-R stone-walled settlements along the Riet River.39,40,41 In specimen MMK 292, there are clear signs of reparative bone formation in the central part of the affected area confirming that the lesion occurred during life (Figure 5b). It may have resulted from trauma, pressure from a cystic lesion of the scalp or an incomplete scrape trephination, as described by Drennan42 on Khoesan crania. If we assume a similar aetiology for the lesion present on the CK skull, we may conclude that it too resulted from such a non-lethal event.

Broom's restoration of the CK cranium now shows many signs of wear and tear. The bones are coated with shellac that has discoloured with age and is chipped in places. The margins of the bones are deeply embedded in plaster, which obscures their edges, whilst the thick layer of shellac obscures the outer surface of the bones. A lateral skull X-ray radiograph was taken to evaluate the feasibility of freeing the bones from the plaster to facilitate a detailed study of its external and internal morphometry, as well as to check for matrix that could be used for dating or to establish provenance. The radiograph showed that the materials used by Broom in the skull reconstruction included a metal strut placed inside the cranial vault for support, whilst the bone fragments and joins were deeply embedded in the plaster, thus complicating any attempt to free them. As an alternative measure, a series of non-invasive investigations including X-ray computerised tomography (CT) scans was conducted to create a 3D computerised model of the skull that would differentiate between bone and plaster.

Computerised tomography scans of the skull

The X-ray CT scans of the reconstructed CK skull were carried out at the South African Nuclear Energy Corporation (Necsa) near Pretoria.43 In view of its relatively large size, the anterior and posterior portions of the CK skull were scanned separately to improve spatial resolution by reducing the size of the scanned object. Scans were first taken with a focal point of 1 mm with corresponding 3D voxel size of 0.195 mm3 and then with a focal point of 3 mm and a voxel size of 0.208 mm3. A series of individual reconstructed 2D slices were stacked to provide a virtual 3D image (tomogram) of the sample. The radio-opacity of the bone versus plaster was computed using the grey value of voxels on a slice image through the reconstruction (Figure 6). Image-ProPlus (IPPLUS) digital software program44 was used in the opacity analysis. The minimum thickness of the cranial bones at different locations on the skull was computed using VGstudioMax 3D visualisation software.45

 

Results

The line profile graph shown in Figure 6 shows the peaks representing the three media - the void, the plaster and the bone. For the bone area, the voxels varied between 1000 and 18 000 in grey values; for the plaster area, the values varied between 800 and 1000; and for the transitional area between the void and the plaster, the values varied between 500 and 900. These results show that the pixel density provided good definition between the bone, the plaster and the metal strut, with the opacity of the bone nearly double that of the plaster matrix (Figures 6 and 7).

The wall thickness analysis menu, used to map the thickness of the cranial bones at different locations on surface images, is shown in Figure 7. The thickness of the bone at different locations varied between 2 mm and 5 mm. Selected 3D reconstructions of sagittal sections through the parietal and occipital bones are shown in Figure 8.

Detailed examination of the supra-orbital region showed no evidence of frontal sinus extension into the preserved portion of this bone, as would be expected if the supra-orbital region was especially thick. No evidence was found for sclerotic bone or bone resorption on the margins, on the surface of the parietal lesion or in the surrounding bone, nor was there any evidence of damage that might have been caused post-mortem.

The sliced tomogram showing the interior of the posterior half of the skull, primarily represented by the occipital bone, is shown in Figure 9. The endocranial surface is obscured in places, probably by materials used in reconstruction (perhaps hessian impregnated with plaster or glue), but there is no evidence of adherent sedimentary matrix that could be used for dating or to assess provenance.

 

Discussion

The X-ray CT scans confirmed that, during reconstruction of the CK skull by Broom, the bones were inserted directly into the plaster so that any attempt to separate them without causing further damage would be risky. The scans also showed that there does not seem to be any matrix adherent to the inner surface of the bones that could be used for dating or determining the stratum in which they were found.

Measurements taken on the reconstructed tomogram show the CK skull to have had a thin-walled cranium (Figures 6, 7 and 8). Where bones were in anatomical contact, there were no overlapping or unnecessary gaps, indicating that the reconstruction did not exaggerate cranial length or modify angulation between bones. Broom's11 claim that the CK skull was one of the most robust that he had examined was based on the well-developed areas of muscle attachments, especially the marked supra-orbital ridges. These and the large size and outline of the incomplete brow ridge and somewhat flattened frontal region, led him to describe the specimen as 'Australoid'. However, the partial suture closure at lambda indicates that the CK cranium represents a mature adult, so that the pronounced muscle markings on the temporal bones are not exceptional for a mature individual with powerful masticatory muscles. Moreover, Broom46<