Researchers believe the new species might be the link between the southern African ape-man Australopithecus africanus and either Homo habilis or a direct ancestor of Homo erectus. The research is detailed in this week's issue of Science.
The newly discovered fossils, a juvenile male and an adult female, were deposited within a single debris flow and occur together in a near articulated state in the remains of a deeply eroded cave system. The sedimentary and geological context indicates that the timing of their death was closely related and occurred shortly before the debris flow carried them to their place of burial.
Through a combination of faunal, U-Pb and palaeomagnetic dating techniques, the age of the rocks encasing the fossils has been determined at 1.95-1.78 Ma. Cosmogenic dating was used to interpret the landscape formation and to determine the depth of the cave at the time.
The skeletons were found amongst the articulated skeletons of a saber-toothed cat, antelope, mice and rabbits. They are preserved in a hard, concrete like substance known as calcified clastic sediment that formed at the bottom of what appears to be a shallow underground lake
or pool that was possibly about 50 meters tall about 1.9 million years ago.
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. It is likely that they could have climbed. Researchers estimate that "both about 1.27 meters, although the child would certainly have grown taller. The female probably weighed about 33 kilograms and the child
about 27 kilograms at the time of his death," said Lee Burger, a paleoanthropologist from the University of the Witwatersrand.
"The brain size of the juvenile was between 420 and 450 cubic centimeters, which is small (when compared to the human brain of about 1200 to 1600 cubic centimeters) but the shape of the brain seems to be more advanced than that of australopithecines."
Citation: Berger et al., 'Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa, Science, April 2010