Sterkfontein - More on a looming or brewing taxonomic controversy?

[Jacques Cinq-Mars]

All,

The following news releases and AJPA Abtract dealing with an apparent rejuvenation of some of the Sterkfontein Australopithecine remains that would subject them to a major taxonomic status change.

Science - Reuters - Friday, Sept. 20

S. African Hominid Fossils May Force Rethink

JOHANNESBURG (Reuters) - South African fossils thought to be key links in the chain of human evolution may not actually be old enough to shed light on the ancestry of modern man, scientists said on Friday.

Research by paleoanthropologists at Johannesburg's University of the Witwatersrand showed the hominid fossils thought to hold clues to the origins of the species Homo sapiens might be too young to claim that role.

The work put the age of fossil skeletons found at the nearby Sterkfontein site at up to one million years younger than previously estimated.

That suggested the species were contemporaries of modern man's ancestors and had already diverged from the line that led to the Homo genus.

"This means we are almost certainly going to have to redraw the family tree," said Dr. Lee Berger, the lead author of the article, published in October's issue of the American Journal of Physical Anthropology.

The World Heritage Sterkfontein site, known as the 'Cradle of Humankind', is fondly referred to by South African President Thabo Mbeki to emphasize the modern world's roots in Africa.

But while the researchers said their work did not detract from the site's significance, they said the site's main fossil cache -- the "member 4" deposit -- was simply not ancient enough at about two million years to contain human ancestors' remains.

"It's just too young," researcher Daniel Lacruz said. "The genus Homo has already been around for several hundred thousand years by the time of Sterkfontein member 4."

The evolutionary chain that links modern man, chimpanzees, and a whole host of extinct fossil species to a common ancestor somewhere about 20 million years ago, has been subjected to fierce criticism since Charles Darwin first proposed the theory of evolution in the 19th century.

A scientific consensus view puts modern man's origins in Africa some 1.5 million years ago, but the route leading to the Homo genus is the focus of intense debate and the research is expected to fuel fresh controversy.

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Business Day (Johannesburg) - September 20, 2002

New Family Tree for Humans?

Jamie Carr And Ernest Mabuza
Johannesburg

STARTLING new research suggests that one of SA's most treasured beliefs that the fossils of the Sterkfontein Caves are the source of humankind may be wrong and out by more than a million years.

This would turn thinking about who holds the title of "matriarch of humanity" on its head.

If fossils that were found at Sterkfontein, such as Mrs Ples of the family australopithecus africanus, are significantly younger than previously thought, it would mean that they are no more than a side-branch of the human family tree.

It would also undermine theories that Mrs Ples could not be a descendant of Lucy of the family australopithecus afarensis another candidate for the "matriarch of humanity" title whose remains were found in Ethiopia in the late 1970s.

"This means that we may have to redraw the human family tree," says Lee Berger, director of Wits University's paleoanthropology unit for research and exploration, whose research is to be published in the October issue of the American Journal of Physical Anthropology.

His claims are likely to unleash great controversy in paleoanthropological and possibly even political circles President Thabo Mbeki frequently uses Sterkfontein's reputation in his domestic politicking and international diplomacy.

It could also reignite the recent fierce debate between Berger and colleague Ron Clarke, discoverer of the ground-breaking Little Foot early human fossil, whose age has also been revised downwards by Berger.

Berger and Clarke were involved in a public spat recently over Clarke's criticism of inaccuracies in a guide to the Cradle of Humankind written by Berger and journalist Brett Hilton-Barber.

Berger and colleagues Darryl de Ruiter and Rodrigo Lacruz said yesterday that the findings would not diminish Sterkfontein's reputation as the Cradle of Humankind. Sterkfontein was declared a World Heritage site in 1999.

"The site remains a unique resource with unparalleled evidence of one of mankind's most critical moments.

The period of 2-million to 2,5-million years ago is where we see some of the most important characteristics of our lineage emerging, such as a large brain, complex tools and possibly even language.

"The cradle never claimed the oldest fossils, but it has the most complete record of human evolution over the last two million years of anywhere in the planet."

Sterkfontein's fossils, such as Mrs Ples, had been believed to be between 2,5-million and 2,8-million years old, and in the case of the Little Foot skeleton, 3,3-million years.

Berger's theory is based on a study of the fossil animals found with the hominins, and a review of new methods of dating Sterkfontein's Member 4 deposit, the richest single site for early hominin fossils in the world.

One of the clearest clues that Sterkfontein was misdated was the presence of 10 species of large mammal that have not been found anywhere else in Africa older than 2,5-million years.

One such is Equus, the predecessor of the modern zebra, which spread down Africa from Asia, and has not been found anywhere on the continent any older than 2,36million years.

For the old dates to be right, all these species would have had to appear suddenly at Sterkfontein significantly earlier than anywhere else.

Other methods of dating lead the researchers to believe that the Sterkfontein fossils are most likely to be about 2-million years old, and that Little Foot may even be younger than Mrs Ples.

The importance of these findings in terms of the human family tree is that where the Sterkfontein fossils had been believed to be the ancestors of modern humans, it now looks unlikely to be so.

Michael Worsnip, programme manager for the Cradle of Humankind site, said the new findings would be good for the site because scientists would now have to battle among themselves on the origins of humanity.

"The idea behind the Cradle of Humankind is advancing research into how the human species developed," Worsnip said. The finding would encourage such debate to take place.

Worsnip said that the site would now be more important for research in the light of the new findings.

Clarke could not be reached for comment yesterday.

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American Journal of Physical Anthropology, Vol. 119, Issue 2, 2002. Pages:192-197.

Brief Communication

Revised age estimates of Australopithecus-bearing deposits at Sterkfontein, South Africa

Lee R. Berger *, Rodrigo Lacruz, Darryl J. De Ruiter
Palaeoanthropology Unit for Research and Exploration, Bernard Price Institute for Palaeontology, University of the Witwatersrand, Johannesburg 2050, South Africa
email: Lee R. Berger (106lrb@cosmos.wits.ac.za)

*Correspondence to Lee R. Berger, Palaeoanthropology Unit for Research and Exploration, Bernard Price Institute for Palaeontology, University of the Witwatersrand, Johannesburg 2050, South Africa

Funded by:
Palaeoanthropology Scientific Trust
University of the Witwatersrand Research Office

Keywords
Australopithecus africanus • Sterkfontein • magnetostratigraphy • faunal dating

Abstract:
The Sterkfontein fossil site in South Africa has produced the largest concentration of early hominin fossils from a single locality. Recent reports suggest that Australopithecus from this site is found within a broad paleontological age of between 2.5-3.5 Ma (Partridge [2000] The Cenozoic of Southern Africa, Oxford: Oxford Monographs, p. 100-125; Partridge et al. [2000a], The Cenozoic of Southern Africa, Oxford: Oxford Monographs, p. 129-130; Kuman and Clarke [2000] J Hum Evol 38:827-847). Specifically, the hominin fossil commonly referred to as the Little Foot skeleton from Member 2, which is arguably the most complete early hominin skeleton yet discovered, has been magnetostratigraphically dated to 3.30-3.33 Ma (Partridge [2000] The Cenozoic of Southern Africa, Oxford: Oxford Monographs, p. 100-125; Partridge et al. [2000a], The Cenozoic of Southern Africa, Oxford: Oxford Monographs, p. 129-130). More recent claims suggest that hominin fossils from the Jacovec Cavern are even older, being dated to approximately 3.5 Ma. Our interpretation of the fauna, the archeometric results, and the magnetostratigraphy of Sterkfontein indicate that it is unlikely that any Members yet described from Sterkfontein are in excess of 3.04 Ma in age. We estimate that Member 2, including the Little Foot skeleton, is younger than 3.0 Ma, and that Member 4, previously dated to between 2.4-2.8 Ma, is more likely to fall between 1.5-2.5 Ma. Our results suggest that Australopithecus africanus should not be considered as a temporal contemporary of Australopithecus afarensis, Australopithecus bahrelghazali, and Kenyanthropus platyops.

Am J Phys Anthropol 119:192-197, 2002. © 2002 Wiley-Liss, Inc.

[Daryl Habel]

Not everyone is yet convinced Berger et al. are correct about this.  Credit goes to Deb (ergaster) for the tip on another forum. See:

http://allafrica.com/stories/200209200655.html

New Twist in the Dating Game
Mail & Guardian (Johannesburg)

September 20, 2002
Posted to the web September 20, 2002

Yolandi Groenewald
Johannesburg

A new calculation of the age of many of South Africa's best-known fossils by a team at the University of Witwatersrand has turned the clock of human evolution forward by a million years.

But not everyone in scientific circles is happy about the way the team rearranged our evolutionary tree.

The researchers found that the Cradle of Humankind heritage site at Sterkfontein near Krugersdorp might be a million years younger than thought. Their recalculation puts Australopithecus africanus, the Southern African apeman who was thought to be a progenitor of humankind, living alongside early members of our own genus Homo.

Lee Berger, director of the Wits Palaeoanthropology Unit for Research and Exploration (Pure), Darryl de Ruiter and Rodrigo Lacruz have revised the estimated age of the australopithecus-bearing deposits at Sterkfontein. Their findings are published in the October issue of the American Journal of Physical Anthropology.

But Tim Partridge, dating expert at the Sterkfontein caves and a geologist with the Climatology Research Group at Wits, slams the claim.

"How can they make this claim when none of them works at the Sterkfontein caves? Their article certainly can't carry much weight. "I want to know where and when they conducted their research," he said.

Partridge says that he and a team of international scientists have also been working on new dating techniques. "Our findings will also shortly be published, but all I can say is that it confirms the results of dating methods used up to now."

The Partridge team's absolute dating techniques allow scientists to calculate dates accurately without comparing the material they find with material found elsewhere.

Phillip Tobias, the world-renowned palaeoanthropologist who popularised South Africa's rich fossil history, wasn't aware of any changes in dating calculations.

"I'll have to read the article first before I can comment on the revised age estimate," he said. "The dating methods that we currently use are based on research of the world's top scientists."

The dating of the remains of early man and his forebears at Sterkfontein has long evoked debate. Unlike in East Africa, where volcanic bedrock allows accurate dating by means of physical and chemical tests, in South Africa, scientists must rely on less exact relative methods.

There are no volcanic rocks at Sterkfontein. Remains are found in dolomite, or limestone, caves. Water melts the limestone and the solution mixes with the sand or bones on the cave floor, forming a concrete-like mixture called brecchia that contains the fossils.

Berger says that biochronogical dating has been the most common method used to date South African sites. This relative method of dating uses index fossils of a known age to date other fossils in the same deposit, including hominins.

"No absolute dating method has come forward and we are reliant on the use of multiple methods to establish relative and absolute ages of the South Africa fossils," the article says.

Partridge devised a geological model for interpreting Sterkfontein's complicated layers of brecchia. He divided the Sterkfontein deposits into age classes called members, labelling them in sequence from oldest to youngest. Member 1 at the bottom would be the oldest and member 6 the youngest.

Paleomagnetic dating, where the magnetic properties of artefacts are studied, estimated that some of South Africa's oldest hominin fossils were up to 3,5-million years old.

Berger's team found that the fauna of Sterkfontein did not tally with those ages and he determined that the fossils could not be older than 3,04-million years.

They now estimate that Sterkfontein member 2, where the Little Foot fossil is being unearthed, is younger than three million years and that Sterkfontein member 4, previously dated at between 2,4-million and 2,8-million years, is between 1,5-million and 2,5-million years old.

"The new facts shake up 30 to 40 years of palaeoanthropology where hominins at Sterkfontein were compared with earlier hominins, when they should've been compared to later hominins," said Berger. "The whole middle branch of human evolution will have to be re-evaluated."

Inconsistencies with the physical characteristics of the hominins found at the Cradle first alerted Berger and his team that something was amiss. Their form showed a more developed hominin than expected from the time.

"Us placing Australopithecus africanus closer to two million years ago resolves much of this debate," De Ruiter said. "We had been comparing the early South African ape-men to the wrong early hominin species elsewhere in Africa."

The new dating technique has specific implications for Little Foot, the most complete early hominin yet discovered.

"There is at present no good evidence that the Little Foot skeleton is as old as has been suggested and it may in fact be younger than fossils like Mrs Ples," Berger said.

Berger's new dates may indicate that Australopithecus africanus, long thought to be an ancestor of the genus Homo, is more likely to be a side branch of the human family tree.