UNIVERSITY OF THE WITWATERSRAND, JOHANNESBURG

About the Discovery

The Cradle of Humankind World Heritage Site. Photo courtesy of Wits UniversityA discovery of early hominid remains may be one of the most significant palaeoanthropological discoveries in recent times. Dating to between 1.78 and 1.95 million, at least two partial hominid skeletons in remarkable condition, as well as abundant fauna, unprecedented in its quality of preservation, have been recovered.

Background

In March of 2008, Prof. Lee Berger of the University of the Witwatersrand, Johannesburg, South Africa, undertook an exploration project with Prof. Paul Dirks, then Head of the University?s School of Geosciences, in the Cradle of Humankind World Heritage site outside of Johannesburg, in order to place known fossil sites onto a map that would permanently record their location. The area is critical as nearly a third of the entire evidence for human origins in Africa comes from just a few sites in this region, and is arguably one of the most explored areas in Africa for evidence of human origins, having been investigated continuously since the first discoveries were made there in 1935.Prof. Lee Berger and his dog Tau enter a cave at the site in the Cradle of Humankind. Picture courtesy of Wits University

Prof. Berger used Google Earth to plot the various caves and fossiliferous deposits, and to locate potential new deposits. Google Earth allowed him to share information with other scientists, and its 3-D capabilities allowed him to begin to identify what caves might look like from satellite images.

At the beginning of this project, there were approximately 130 known cave sites in the region and around 20 fossil deposits. Soon he began finding dozens of previously unidentified caves and fossil sites.

By July 2008, through using Google Earth complemented by significant legwork on the ground, Prof. Berger had discovered almost 500 caves that scientists had not previously identified. Included in this were more than 25 fossil sites that had been unknown to science. In late July, Prof. Berger noted on Google a series of caves running along a fault line that that appeared to have clusters of trees that typically marked cave deposits. On the 1st of August 2008, whilst Prof. Dirks mapped the recognised cave system, Prof. Berger proceeded into the uninvestigated area with his dog Tau, a ridgeback, who accompanied him on almost all his explorations. Almost immediately he discovered a rich fossil site that was unknown to science, in the vicinity of more than threedozen caves that had been unrecognised by previous researchers.Prof. Lee Berger and Dr. Job Kibii at the Malapa site in the Cradle of Humankind, moments after the discovery. Photo courtesy of Wits University

On the 15th of August 2008, Prof. Berger returned to the site with his post-doctoral student, Dr Job Kibii and his nine-year-old son Matthew. Within minutes, Matthew had discovered the first remains of early human ancestors - a clavicle, or collarbone. Remarkably, Prof. Berger had done his PhD thesis on this very bone, when he had studied the hominid clavicle, scapula and humerus. On the opposite side of the block, Prof. Berger discovered a jawbone with a canine tooth of a hominid. The find would soon be prepared and identified as part of a partial skeleton of a juvenile hominid, around 9 ? 13 years of age.

On the 4th of September 2008, Prof. Berger returned to the site with more than a dozen colleagues, with high expectations of recovering more fossils. After four and a half hours, the team had not discovered a single element that they could conclusively be identified as hominid. As the group took a break, Prof. Berger went to the edge of the small pit in the middle of the site and noted a bone sticking out of the rock. It was clearly the humerus of a hominid. Astounded, Prof. Berger went down into the pit and realised that it articulated with a scapula and as he put his hand against the wall, two hominid teeth literally fell into his hand. Remarkably this second find was not the same individual that Matthew had found, but a second skeleton of an adult female.

Prof. Lee Berger leads the team onto the Malapa site in the Cradle of Humankind. Photo courtesy of Wits UniversityIn the months to follow the site has produced arguably the most remarkable assemblage of early human ancestors ever found, including what are probably the most complete skeletons of early hominids ever discovered and by far the most complete remains of any hominid dating to around two million years ago. The fossils, one juvenile male, one adult female, occur together in near articulated state in the sedimentary remains of a deeply eroded cave system, where they were laid down by a single debris flow, indicating the timing of their death was closely related, and occurred shortly before the debris flow carried them to their place of burial.

A further important aspect of the find is that a male and female were found together, and are respectively a juvenile and an adult. The sex of the fossils can be determined from the morphology of the jaws and hips, whilst the age of the juvenile has been determined from its dentition making it about 11 to 13 years old in human terms. In contrast the adult female has strongly worn teeth suggesting an age in her late 20?s or perhaps even older. Both individuals are about 1.27cm tall.

Prof. Lee Berger with some of the partial remains of Au. sediba. Photo by Brett Eloff, courtesy of Wits UniversityThrough a combination of faunal, U-Pb (Uranium ? Lead) and palaeomagnetic dating techniques, the age of the rocks encasing the fossils has been determined at 1.95-1.78 Ma. Dating involved a double blind U-Pb date, conducted independently in laboratories in Bern and Melbourne. This is a first in the dating of flowstone deposits in the Cradle of Humankind. Once an absolute date had been obtained, palaeomagnetic analysis was used to constrain the age of the debris flow encasing the fossils. Over 130 elements have been recovered to date, and more are emerging.

The partial skeletons are described in two papers in the prestigious journal Science, due to be published on the 9th of April 2010, as a new species of early human ancestor called Australopithecus sediba (sediba meaning natural spring or wellspring in Sotho). The species is suggested to be a good candidate for being the transitional species between the southern African ape-man Australopithecus africanus (the Taung Child, Mrs. Ples) and either Homo habilis or even a direct ancestor of Homo erectus (Turkana boy, java man, Peking man).

The species has long arms, like an ape, short powerful hands, a very advanced pelvis (hip bone) and long legs capable of striding and possibly running like a human.

The skeletons are found among the articulated skeletons of sabre-toothed cats, antelopes, mice and rabbits. They are preserved in a hard, concrete like substance known as calcified clastic sediments that formed at the bottom of what appears to be a shallow underground lake or pool that was possibly as much as 30 to 50 meters underground at the time. It is not known how these precious skeletons came to be in this pool, but it appears that they may have taken a significant fall. No carnivores or scavengers reached their bodies. Remarkably it is interpreted that the individuals described died at, or around the same time as each other, and thus would almost certainly have known each other in life and may very well have been related.

An international team of over 60 scientists is involved in the project. The authors on the Science papers are:

First paper
Australopithecus sediba : A New Species of Homo-like Australopith from South Africa Lee R. Berger, Darryl J. de Ruiter, Steven E. Churchill, Peter Schmid, Kristian J. Carlson, Paul H.G.M. Dirks and Job M. Kibii.

Second Paper
Geological Setting and Age of Australopithecus sediba from Southern Africa Paul H.G.M. Dirks, Job M. Kibii, Brian F. Kuhn, Christine Steininger, Steven E.
Churchill, Jan D. Kramers, Robyn Pickering, Daniel L. Farber, Anne-Sophie M?aux,
Andy I.R. Herries, Geoffrey C. P. King and Lee R. Berger