They have discovered a new type of hominid in South Africa. The fossils with an age of about 1.9 million years show features of both the Australopithecus and the homo species. The new type of hominid, Australopithecus sediba, could therefore be an ancestor of the homo species. The formerly unknown transitional form, which is being introduced in the latest edition of "Science", is supplying new findings for the genealogy of the human being.
On 15th August 2008, Matthew Berger, the young son of the paleoanthropologist Lee Berger, found the fragment of a human-type clavicle in South Africa. The first excavation team to work on the new site in Malapa, north of Johannesburg, was the Swiss Field School of the Anthropological Institute of the University of Zurich under the leadership of Peter Schmid. In the meantime, the Zurich-based excavation team has found more than 180 elements of at least four individuals who could be ancestors, unrecognised until now, of the human being.
Peter Schmid and his research colleagues from the University of the Witwatersrand, the Texas A&M University, Duke University and James Cook University have now described two figures in the latest edition of "Science". The adolescent individual is comprised of fragments of a skull and lower jaw as well as a partial skeleton. The adult is made up of individual teeth, fragments of the lower jaw and a partial skeleton. "These skeletons are better preserved and more complete than that of the well-known Lucy", states Peter Schmid from the Anthropological Institute of the University of Zurich.
Peter Schmid goes on to say: "The fossils are between 1.78 and 1.95 million years old". The discoveries do not fit any kind of hominids known until now - they therefore form a new milestone in the history of humanity. On the basis of the age and morphology, the researchers are cautiously allocating the new type of hominid to the Australopithecus species. They have given it the name of Australopithecus sediba, which means "water-well" or "spring" in the seSotho language. The Australopithecines encompass various types such as the Australopithecus africanus, the Australopithecus afarensis or the Australopithecus garhi. They appeared a good 4 million years ago and died out approximately 1.4 to 1.5 million years ago. They have only been found on the African continent, and from them developed the homo species, and thus the homo sapiens.
A small skull with similarity to the homo
As Peter Schmid and his colleagues write in "Science", the new kind of hominid has a relatively small skull - a typical feature of the Australopithecus. The capacity of the skull amounts to only 420 cubic centimetres and is significantly smaller than that of the Australopithecus africanus with an average of 480 cubic centimetres.
On the other hand, the outline of the face differs from the Australopithecus africanus through narrower cheekbones and the contour of the upper jaw which runs diagonally downwards. The lower jaw shows no sign of a fleeing chin and the canine tooth is rather narrow and small. The pectoral girdle equates to the typical Australopithecus pattern: The joint of the shoulder-blade is clearly directed upwards and the alar edge is very strong. The ends of the joints of the upper arm are massive. The lower arm bones are long, similar to those of monkeys. The finger bones are robust, curved and have strong contact points for the tendons of the flexors which indicates strong climbing hands.
Numerous characteristics of the thighs, the knee joints and the ankle joints lead to the presumption that Australopithecus sediba moved in a similar way to the other Australopithecines. The ankle joint and the heel bone are shaped in such a way that the foot was able to be turned more strongly towards the inside, which is an advantage when climbing. However, the hominids could stand upright on the ground and walk on two legs. The bones of the legs nevertheless seem to be longer than those of the Australopithecines.
A transitional form
"The entire build of the body corresponds to that of a type of human in the Australopithecine adaptation stage", says Peter Schmid. He believes that the Australopithecus sediba is a descendant of the Australopithecus africanus. On the other hand, some characteristics of the musculoskeletal system permit the conclusion that this new type shows more special features of the earlier representations of the homo species than all the other Australopithecus types. The pelvis, for example, corresponds much more to that of the homo. In addition, the Malapa skull shows several similarities with the homo erectus.
Up until now, there has been no certain connection between the Australopithecus and homo species. "Our type of hominid could be an ancestral form of the homo species", says Peter Schmid. It is also possible that it is a close relation of that kind of ancestor which, for a period of time, existed alongside the first representatives of the homo species. The skeletons from Malapa in any case show a transitional form of a hominid which was small in size and lived more in the trees to a two-legged species that possibly lived on the ground, for example the homo erectus.
Lee R. Berger, Darryl J. de Ruiter, Steven E. Churchill, Peter Schmid, Kristian J. Carlson, Paul H.G.M. Dirks and Job M. Kibii: Australopithecus sediba: a New Species of Homo-like Australopith from South Africa, in: Science, 9th April 2010, Vol 327, issue 5974
Contact:Dr. Peter Schmid, Anthropological Institute and Museum of the University of Zurich
Beat Müller | idw
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