Scientists at the University of Liverpool have dated an ape-man skeleton at 2.2 million years old suggesting that it may not have been part of the ancestral tree leading to humankind as originally thought.
Liverpool researchers worked in collaboration with colleagues at the University of Leeds to analyse the skeleton, which was found in 1997 in Sterkfontein cave in South Africa. Known as ‘Little Foot’, it was known to be between two million and four million years old, but the team has now dated it precisely to 2.2 million years old.
These new findings reveal that the ape-like creature – part of the Australophithecus africanus family – may not be the immediate ancestor of human beings as some experts originally thought. This is because the team found that ‘Little Foot’ lived after the arrival of the stone tool makers, Homo habilis, raising the possibility that this family was more of a side branch of the human evolutionary tree.
Dr Alfred Latham, from the University’s School of Archaeology, Classics and Egyptology said: "‘Little Foot’ is known to have stood on two feet, standing approximately 130cm tall and having a brain not much larger than a modern chimpanzee. It was discovered cemented in layers of stalagmites and archaeologists are continuing to extract the skeleton from the hardened deposits. We believe that ‘Little Foot’ either fell down a shaft or somehow got trapped in the cave and died there. The remains were preserved in the stalagmite layers and it is these layers that have helped our team to date the skeleton."
In order to ascertain the age of the skeleton, Dr Latham, together with Dr Bob Cliff and Jo Walker at the University of Leeds, used a technique called uranium-lead dating. Stalagmite layers contain traces of radioactive uranium, which eventually decays to form lead. The team measured the amount of uranium and lead in the stalagmite layers to form an accurate date for their age and for that of the skeleton.
Dr Latham continued: "Liverpool was the first to obtain rock samples from the cave in 1997 when the skeleton was found. At that point the team dated the layers at 3.3 million years old using magnetic analysis and evidence from animal remains.
"Further investigation by an American team subsequently dated it at 4.29 million years old, which was considered controversial. It was clear from these varying results that another technique was needed in order to place the species within the evolutionary tree. Uranium-lead analysis – an established technique in geology – has never been used on an archaeological site of this kind before, but it has proved to be highly successful."
Uranium-lead analysis has proved to be more accurate than other dating techniques as it does not rely on animal remains or sediment traces surrounding the excavation site. Animal remains or sediment traces are often buried in many layers of hardened deposits making it difficult for archaeologists to pin point exactly where and when the specimens were in existence.
Dr Latham added: "Though these caves hold by far the most numerous ape-man deposits in the world they have been very difficult to date accurately. We have now opened up the way to dating more of these important fossils using the uranium-lead technique."
Dr Latham is now working on another site in Africa similar to Sterkfontein. It is thought to hold the remains of the same ape-man species but these are thought to be approximately 3 million years old. If this is confirmed it means that the species could still be ancestral to humans.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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