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Cradle of Humankind

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The Cradle of Humankind World Heritage site[1][2] in South Africa comprises three localities containing numerous fossil-bearing caves that have been recognized for their significant contribution to our understanding of human origins in Africa. The core area was proclaimed a World Heritage site in 1999 and additional sites were later added.

Geographical location

The sites which jointly make up the COH World Heritage site are located in three areas of South Africa: Makapansgat, in the Limpopo Province; Taung in the Northwest Province and the area around the well known sites of Sterkfontein, Kromdraai and Swartkrans, which is situated north and west of the greater metropolitan area of Johannesburg in the Gauteng Province. The Taung site is found in tufaceous cave deposits formed on the edge of the Kalahari dolomitic escarpment, while the Makapansgat limeworks site and the sites within the Cradle of Humankind are situated within caves in karstic terrain [3].

History and importance

The dolomitic cave deposits of South Africa and in particular those of the COH , have yielded one the richest record of both hominin and mammalian evolution in Africa[4]. Fossils were first recognized in southern Africa deposits in the early 20th century, but it was the discovery of the Taung child skull from the Buxton limeworks in 1924 that led to the recognition of the importance of these cave sites [5]. Two critical discoveries followed shortly thereafter that brought attention to the area that would become known as the Cradle of Humankind. The first was the discovery of the first adult australopithecine (‘ape-man’) remains from Sterkfontein in 1936, and the discovery in 1938 of another type of ‘ape-man’ at Kromdraai [6]. The two finds demonstrated, for the first time, the possibility that not all hominins were the ancestors of living humans and that there may have been a number of other branches of ape-men who died out[4]. While hominins have often been the focus of research in the COH since 1936, the remains of large numbers of other vertebrates have been recovered from these sites[3]. Unlike in lacustrian (lake) and surficial terrestrial (land) deposits such as those in East Africa, the dolomitic caves of South Africa provide an ideal protected environment for fossilization [4]. Therefore the fossil vertebrate material, when recovered, is generally in very good condition[3]. The vertebrate animal fossils from South African caves are of particular interest because of their completeness and variety, and because of the differences in composition from East African sites, that is, the record in South Africa is often better preserved and in better condition than the very well known fossils from sites such as those in Ethiopia, Kenya and Tanzania [4]. Invertebrate remains, coprolites, egg-shells, fossilized hair and fossil plant material are also preserved and provide a rich record of life in the geological past[3]. Possibly the most remarkable aspects of the South African caves are the sheer numbers and densities of fossils that are found in some localities, with quite literally hundreds of thousands of bones packed into relatively small areas, and the completeness of many articulated skeletons of various vertebrate species[3]. These articulated remains, including those of hominins, carnivores, and bovids, offer a valuable record of individual species morphologies as well as insight into taphonomic processes[4]. Because of the quality of preservation in the calcium carbonate based breccias and flowstones, the bone and tooth surfaces are also in extremely good condition and offer researchers a glimpse at bony detail not available on bones and teeth recovered from terrestrial, lake and river formed deposits[3].

Dating of the sites

Dating of the deposits and individual fossils has however proved to be challenging. The first efforts to date the sites in the COH involved comparing them with European and East African sites, but recent advances in geological understanding, and geophysical and radiometric methods have shown promise in accurately dating South African fossils and breccias[3].

The hominin fossil record

Hominins are represented in the South African cave sites by over 1000 catalogued specimens from more than 11 different cave deposits. Hominin remains include adults and juveniles as young as several months in age, complete skulls, ossicles, and postcranial remains that cover every aspect of the skeleton[4]. At least four and possibly more species of early hominin are found in the South African cave sites[4]. While the hominin fossils from South Africa are not nearly as old as the oldest hominin sites in East Africa (East African fossil hominins may date back over six million years while those in South Africa are probably all less than three million years in age), the South African examples are important because they are almost always more complete and are found in the presence of a much greater range of vertebrates[4]. In addition the high concentrations of fossils in the South African caves have offered taphonomists and palaeo-ecologists the opportunity to access and study them much more easily than sites in East Africa and elsewhere[3]. Also, the period of time which the South African hominins cover represent some of the most critical periods in human evolution, where some of the most important changes have taken place[4].

Deposition of the cave infills

It is now recognized that the fossil bearing breccias of the South African caves accumulated over many hundreds of thousands if not million of years, and in a wide variety of palaeo-environments[3]. In fact bone accumulations are still being made in the area and undergoing fossilization even today. Nevertheless, it is clear from the vertebrate fossil record that most of the early hominin-bearing breccias accumulated under very different environmental conditions than those present in the dolomitic regions today. Some experts suggest that the area was a riverine forest environment while others believe it was more of a savannah grassland, in fact it is probable that environments changed over time in the COH[4]. Accumulation of bone in the Cradle of Humankind caves has occurred in a variety of ways. In many cases animals simply fell into the caves and were killed or trapped, while in others, scavengers or predators dragged their corpses in[3]. Some animals actually lived and then died in the caves.

Fossilization

Bones may be preserved in a wide variety of conditions, but at the COH they were mainly preserved by calcium carbonate. Precipitation on the roofs of the limestone caves caused droplets of calcium carbonate to drip down and effectively ‘cement’ sediments and bone together creating breccia. The COH breccias are interlaced with flowstones, stalactites and stalagmites comprised of purer calcium carbonates than the breccias which are contaminated by other debris often giving them distinctive colours[3]. Fossils occur in almost every situation within the cave and the quality of preservation is highly dependant on immediate local conditions.

Fossil sites within the Cradle of Humankind

References

  1. Fossil Hominid Sites of Sterkfontein, Swartkrans, Kromdraai, and Environs
  2. Cradle of Humankind official website
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 L.R. Berger (2005). Working and Guiding in the Cradle of Humankind. Prime Origins. 
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Hilton Barber, B. and Berger, L.R. (2001). Field Guide to the Cradle of Humankind. Struik. 
  5. P.V. Tobias (1984). Dart, Taung and the 'Missing Link'. Institute for the Study of Man in Africa. 
  6. R. Broom (1950). finding the Missing Link. Watts, London.