International team discovers new species of hominid

An international team of scientists has described a new fossil find and a new species of hominid, Australopithecus sediba, thought to be at least 2 million years old in an area of South Africa known as the Cradle of Humankind. Lawrence Livermore National Laboratory scientist Dan Farber's work involved describing the geological, geochronological, geomorphological and faunal context of the Malapa site - which holds the fossils of an adult and a juvenile of the new species. The research appears in a pair of papers in the April 9 issue of the journal, Science.

Australopithecus is a genus of extinct hominids, made up of the gracile australopiths, and formerly also, the robust australopiths. The new fossils of Au. sediba reveal its skeletons are exceptionally well preserved, proving unique insight in the period when the earliest members of the genus homo evolved. Based on the morpho-metrics of the various skeletal parts, Sediba appears to be a transitional form between early australopithecines and early members of the genus homo. It may, in fact, replace other candidates such as Homo habilis as our distant ancestor. Because of this, the new species was named Sediba (meaning fountain) reflecting its position at the base of the evolutionary tree.

Using the Laboratory's Center for Accelerator Mass Spectrometry, Farber and a team of researchers, including ex-LLNL post-doc Anne-Sophie Meriaux of the University of Newcastle and Geoff King of the Institut de Physique du Globe, were able to quantify the degree of post fossil landscape change. In other words, they were able to track the evolution of the landscape from where the fossils originally were deposited to where they were found in the present day. Using rare radioisotopes formed by the interaction of cosmic rays with rocks at the Earth's surface, Farber was able to provide a paleo-ruler by which he measured the amount of material lost since the time the fossil was deposited.

Australopithecus sediba is possibly the most important found to date and the site has produced arguably the most notable assemblage of early human ancestors ever found, including the most complete skeletons of early hominids ever discovered and the most complete remains of any hominid dating to around 2 million years ago, Farber said. The species may 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 two hominid specimens lived in the area between 2.3 million to 1.5 million years ago. The fossils are encased in water-laid sediments that were deposited along the lower parts of what is now a deeply eroded cave system. They were buried together in a single debris flow that petrified soon after deposition in a cave inaccessible to scavengers.

Hominid fossils and associated faunal and archaeological remains occur throughout the Cradle of Humankind including the sites, Sterkfontein, Swartkrans, Kromdraai and Coopers.

"While South Africa has long been known for its rich deposits containing early hominid remains, the debris-flow-hosted deposits have proved challenging for scientists to assess the timing and nature of the fossilized remains. My job was to quantify the degree of post fossil landscape change," Farber said. "In fact, I was invited to work in South Africa (just weeks before the first fossils were found at this site) to try for the first time to quantify the post Miocene landscape evolution and work out the type of landscape that our earliest ancestors inhabited. The outcome of lead researcher Lee Berger's initial work is that there was a major new fossil find, and possibly one of the richest ever, which has focused our research efforts for the time being."

Source: DOE/Lawrence Livermore National Laboratory