The human fossils, close to 2 million years old, have been classified as a new species: Australopithecus sediba. Australopithecus means "southern ape" and Sediba, taken from the local South African language seSotho means "natural spring, fountain or wellspring".
The findings represent some of the most significant scientific discoveries of recent years and were published today in the scientific journal Science.
Dr Robyn Pickering of the School of Earth Sciences at the University of Melbourne who was one a team of international and Australian scientists to accurately date the sediments surrounding the fossils says, "We are now able to fill in the gap of what happened 2 million years ago in the beginnings of our species."
"It has never been clear where our own genus Homo came from - this new discovery, Australopithecus sediba could answer these questions," she says.
Researchers say this species appears to be a transitional form, maybe the best yet found, between early australopithecines and early members of the genus Homo, thereby replacing other candidates such as Homo habilis (the tool making 'handy' man from east Africa) as the distant ancestor of Homo sapien.
The Sediba fossils are exceptionally well preserved, and therefore provide a unique insight in the period when the earliest members of our genus evolved.
Sediments from surrounding and supporting the fossils were analysed by several research teams.
Using a state-of-the-art uranium lead dating technique, conducted independently and in parallel by Dr Pickering at the University of Melbourne and her former PhD supervisor Professor Jan Kramers from the University of Bern in Switzerland, they produced an identical age result confirming the sediment was close to 2 million years old.
"Together with palaeomagnetic dating of the sediments more closely surrounding the fossils by Andy Herries of UNSW and our team of colleagues led by Professor Paul Dirks from the University of Townsville, we were collectively able to provide an age of 1.95-1.78 million years for the fossils," Dr Pickering says.
"This is the first time, in relation to these renowned caves in South Africa, that we have been able to achieve such high-quality age control."
"Knowing how old these early human (hominin) fossils are, is critical to our knowledge of where this newly found species fits into our family tree," she says.
Associate Professor Jon Woodhead, who heads the Isotope Geosciences laboratory in the School of Earth Sciences at the University of Melbourne, noted "This is a highly significant find and I congratulate Robyn and her colleagues on their discovery."
"Only very recently have we been able to develop the technologies required to allow precise dating of cave sediments such as those found in intimate association with these new fossils."
"This really is the beginning of a 'new era' as such methods have much to contribute to studies of global climate change, biodiversity and, in this case, human evolution."
"The University of Melbourne is a world leader in this area and we are proud to have been able to contribute to this important discovery."