The origins of The Cradle

  • September 02, 2012

Mrs Ples”, which was initially named Plesianthropus transvaalensis, but has been retrospectively identified as an adult Australopithecus africanus.

Two and a half billion years ago, the site occupied by the “Cradle of Humankind” in Gauteng was nothing like it is today. According to geological evidence, the land was once submerged by a giant inland sea. This gave rise to the optimum conditions for the formation of caves and ultimately the fossil deposits found in the area today.

According to archaeologist, Morris Sutton, “Within the last 20-50-million years, the caves were formed inside dolomitic rock. Slightly acidic groundwater dissolved solution cavities beneath the water table. Over time, the water table dropped deposits. These deposits accumulated over time and the caves became air-filled voids in which stalactites and stalagmites could form. Water from the surface percolating through cracks in the dolomite absorbed calcium carbonate. On reaching the cavern ceiling, carbon dioxide was released, and a thin film of calcium carbonate was formed.”

Dr. Morris Sutton, one of the principal researchers and the project archaeologist for the Swartkrans Paleoanthropological Research Project at Maropeng.

“Four and a half million years ago, the first caves became visible to the surface. These were not traditional caves but really sinkholes. For this reason there are a number of deposits of breccia on cave floors, which are an aggregation of soil, rock and bone that fell into these sinkholes. An accumulating factor is that there were a lot of predators in the area at the time.”

Visitors to The Cradle may be forgiven for thinking that the area is the actual birthplace of humankind: the name of the Visitors’ Centre, Maropeng, comes from an old Setswana word, meaning, “returning to the place of origin”. In actual fact, the oldest hominid specimen in the world was found in Chad in 2001. The fossil skull is called Tomaï, meaning “hope in life”, and is dated as being over 7 million years old. Other specimens that are dated as being as old as 4.4 million years have been found in Ethiopia and include the Australopithecus afarensis specimen, “Lucy” which was a major fossil discovery in the 1970s. Ethiopia, like South Africa, also has its own unique geological features which make a prime site for fossil discovery. Millions of years ago, a volcano erupted at what is now the Hadar site, later this land became cleft open, making fossils available on the surface to be discovered. 

 As a result of the majority of fossil finds being made in Africa, scientists postulate that humankind originally came from Africa, although it is difficult to be more specific about the exact location. What makes the fossil sites in South Africa unique is the completeness of the fossil finds in the area. The quality of these fossil finds is due in no small part to excellent excavation techniques.  An example of these are the techniques pioneered by Bob Brain, the palaeontologist responsible for dating and demarcating the various zones at the Swartkrans dig site.

Brain was not the only scientist to make his mark on the area, with many of his predecessors having made some of the most important palaeoanthropological finds of the time. According to Sutton, “Robert Broom , who had already spent many years searching for and discovering dinosaur fossils in the Karoo area of South Africa, was one of the few that believed Dart was right in proclaiming the Taung Child as a hominin in the human evolutionary line. Broom realised the geology around Sterkfontein was similar to that in the Taung area and began searching for hominin fossils there. Two decades later Broom discovered “Mrs Ples”, which was initially named Plesianthropus transvaalensis, but has been retrospectively identified as an adult version of the Taung Child specimen of the Australopithecus africanus. Dart and Broom discovered a number of other fossils in the area, including specimens of Australopithecus robustus (sometimes also called and Paranthropus). Specimens of Homo ergaster have also been found at Swartkrans. Some of these finds have been dated as belonging to simultaneous periods and scientists believe that as many as five different hominid species may have coexisted in the same area.

Sutton says, “After finding only parts of skeletons of animals within the cave deposits, Dart concluded the hominins were using the bones as tools and as weapons for hunting. Bob Brain, working at Swartrkans and pioneering the field of taphonomy (the study of the processes of fossilisation), tested Dart’s hypothesis. He was able to show that factors affecting a body’s skeleton after death, such as predators’ chewing and crushing, scavenger gnawing and natural weathering result in only the denser parts of the skeleton surviving. Brain proved that the bone assemblages in the caves were there, not because of collection by hominins, but due to predation by carnivores using the caves as dens.  Hominins were not predators, using bones as tools and weapons, but were instead prey.” 

Sutton continues, “What happened next was an example of real scientific spirit. Dart was so impressed by Brain’s work, even though it had overturned his own initial theories, that he nominated Brain as the Young South African Scientist of the Decade, a nomination which secured Brain the accolade.” Even more interesting is Sutton’s final comment on the matter, “However Brain did recover bones from Swartkrans with small striations on the ends suggesting use by the hominins. His actualistic experiments digging in the soil with modern bones showed the fossils had been used as digging tools, probably for food, by the hominins; demonstrating that Dart was at least partially right.”

The story of humankind’s tool using appears to still be unfolding. As a result of the outstanding work that has been conducted at the many Cradle of Humankind fossil sites, South Africa continues to yield some of the most important historical fossil finds in the world.
 

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