Thursday, April 29, 2010

Sediba - Natural Spring

Earlier this month a team of scientists at the Institute for Human Evolution of the University of the Witwatersrand in Johannesburg announced an amazing discovery. It was nothing less than the holy grail of paleoanthropologists – the fossilized remains of a new species of hominid. Excitement spread through the expert community at once, but the discovery caught the imagination of the general public also. It’s not hard to understand why. Few prehistoric issues are more intriguing than our linage and where it branches from the great apes, our close genetic relatives. There is even some possibility that the new species – named Australopithecus sediba (Sediba is a natural spring in the Sotho language) - is a link between the previously known southern African Australopithecus specie - Australopithecus africanus – and Homo habilis or Homo erectus. In other words a connection between the two genera, one of which is our own.

Lee Berger with sediba
The first Australopithecus specimen was also discovered by a Wits professor. Raymond Dart wrote up his discovery of the so-called Taung Child in the journal Nature in 1925. Other discoveries followed first by Dart and then under the leadership of Dart’s successor, Professor Phillip Tobias. Several are from the same area where the new specimens where found. Pictures of Dart and Tobias, with friends, are below:

It seems that Australopithecus evolved some four million years ago in east Africa and spread over much of the continent. It is thought to have become extinct some 2 million years ago. Thus the age of the new specimens is a very important issue. Paul Dirks, then the head of the School of Geosciences at the university, was involved with the dating issues. They attacked the problem three ways. Various other fossil creatures were found in the same sediments; several of these are well-known as are their periods of existence. Next, the magnetic polarity reverses which took place in the geological past put the fossils between 1.78 and 1.95 million years of age. Finally uranium/lead dating puts them at around 2 million years. 2 million years mean that sediba lived in the same time frame as the homo species; possibly they were contemporaries. More controversially, Berger has suggested that humans may be descendents of sediba. Reaction to that has been mixed. Either way it is a branch of our tree which was unknown before.

The species had long ape-like arms, short hands and long legs which might have made it possible to run or walk like a human. Two more specimens have been discovered, preserved in a hard conglomerate of calcified clastic sediments, apparently deposited at the bottom of an underground lake nearly two million years ago.
Makapansgat where some earlier specimens of Australopithecus were discovered.

The New York Times featured Lee Berger and his young son, Matthew, with his dog, Tau, at the site, and delighted in the story of the boy picking up the first piece of fossilized clavicle bone. Tau means Lion in Setswana, which is the unofficial language of Botswana but also widely spoken in South Africa. Apparently the dog ran off and Matthew followed, returning with the fossil. It would have been an even better story if the bone had been dug up by Tau! The full story of that first discovery is at

What makes the discovery particularly remarkable is the location. The specimens were found at the Cradle of Mankind, a world heritage site where some of the Australopithecus africanus specimens were discovered. It is a rich collection of (now filled) caves which seems to have hosted a variety of species for millennia. Now it seems it hosted at least two different species of hominid over time.

The scientists have been working with the specimens, and finding additional ones, for eighteen months. I recall Paul Dirks telling me about a year ago that he was working on dating a marvelous fossil discovery at the Cradle. At the time we were discussing the use of certain geophysical techniques to try to find additional filled caves and promising sites in the area. In the end none of the high tech was necessary. It all came down to a boy and his dog.

Michael -Thursday

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