AUSTRALOPITHECUS SEDIBA: DISCOVERY SITE AND SIGNIFICANCE

AUSTRALOPITHECUS SEDIBA

replica of skull of Australopithecus sediba

Australopithecus sediba, which means "southern ape, wellspring", lived some 2 million years ago. Discovered in 2008 by the nine-year-old son of paleoanthropologist Lee Berger of the University of the Witwatersrand in a cave South Africa, it was good at climbing trees but also walked upright on the ground. Some scientists regard it as an the evolutionary link between the genus Homo, which includes modern humans, and the australopithecine, ape-like species that are believed to have preceded Homo.

Scientists are still attempting to piece together exactly how Australopithecus sediba fit into the evolutionary history of humans. The age of the skeletons and their mix of traits has convinced Berger that Australopithecus sediba may be a direct ancestor of our genus, Homo, and is the most plausible known ancestor of archaic and modern humans. However, this theory has been controversial. Few other paleoanthropologists share Berger’s view.

A 2011 analysis of some of A. sediba's bones revealed a combination of human and more apelike traits, which Associated Press described as being “like a snapshot of evolution in action.” After a 2013 analysis it was determined that A. sediba and an older South African species, A. africanus, appear more closely related to early humans than other australopithecines like the famous "Lucy" from Ethiopia.

A. sediba bones show a head-to-foot combination of features of Australopithecus and the human genus, Homo. "It's as if evolution is caught in one vital moment, a stop-action snapshot of evolution in action," said Richard Potts, director of the human origins program at the Smithsonian Institution. He was not among the international research team, led by South African scientists. Their research was published online in the journal Science. The journal published five papers detailing the findings, including separate reports on the foot, hand, pelvis and brain of A. sediba. [Source: Randolph E. Schmid, AP, September 8 2011]

The fossils of Australopithecus sediba were accidentally discovered by Mathew Berger, Lee Berger's nine-year-old son, in 2008 in a cave in the Malapa Nature Reserve, in the fossil-rich cave region of Malapa, 40 kilometers northwest of Johannesburg, South Africa. Scientists later excavated an almost complete skull, together with shoulder bones, a hand, wrist bones and ankle bones. Two key specimens were discovered — a juvenile male as developed as a 10- to 13-year-old human and an adult female maybe in her late 20s or early 30s. Professor Berger announced the discovery in 2010.

Significance of Australopithecus sediba

Endocast of Australopithecus sediba

Randolph E. Schmid of AP wrote in 2011: “An analysis of 2 million-year-old bones found in South Africa offers the most powerful case so far in identifying the transitional figure that came before modern humans — findings some are calling a potential game-changer in understanding evolution. The bones are from Australopithecus sediba. The research places that pre-human branch of the evolutionary tree as the best candidate to be the ancestor of the human line, said Lee R. Berger of the University of Witwatersrand in South Africa. [Source: Randolph E. Schmid, AP, September 8 2011]

Scientists have long considered the Australopithecus family, which includes the famous fossil Lucy, to be a primitive candidate for a human ancestor. The new research establishes a creature that combines features of both groups. Berger said the brain, hand and foot have characteristics of both modern and early pre-human forms that show a transition under way. It represents a bona fide model that could lead to the genus Homo, Berger said.

Berger has argued that Australopithecus sediba may represent an intermediate form between the primitive australopiths and our genus, Homo. Josh Fischman wrote in National Geographic magazine, “The evidence they point to includes an australopith's little brain (with some curiously modern features), apelike shoulders, and arms adapted to climbing in trees — attached to a bizarrely modern hand with the precision grip of a toolmaker. According to the researchers, the adult female's foot presents an even odder melange; her mostly modern ankle is connected to a heel bone more primitive than that of A. afarensis — Lucy's species — which is at least a million years older. In a science known for its contentiousness, such a claim will surely not go unchallenged. But no one disputes that the Malapa fossils are unprecedented. [Source: Josh Fischman, National Geographic , August 2011]

"It really is a jaw-dropping find," says Carol Ward, a paleoanthropologist at the University of Missouri who studies the evolution of apes and early hominins (a term for humans and other nonape primates; some researchers prefer the older term, hominin). "We have no other collection of fossil skeletons, until the Neanderthals just over 100,000 years ago, that are so articulated, so complete."

When asked if Australopithecus was a missing link, Darryl J. DeRuiter of Texas A&M University said that if scientists prefer the terms "transition form" or "intermediary form": "This is what evolutionary theory would predict, this mixture of Australopithecene and Homo," DeRuiter said. "It's strong confirmation of evolutionary theory." But it's not yet an example of the genus Homo, he said, though it could have led to several early human forms including Homo habilis, Homo rudolfensis or Homo erectus. [Source: Randolph E. Schmid, AP, September 8 2011]

These articles "force a rethinking of how traits are coupled together in human evolution," the Smithsonian's Potts said. "For example, in previous definitions of our genus, the leading edge in the emergence of Homo has been brain enlargement. The sediba bones show, however, that reorganization of the brain and pelvis typically connected with the evolution of Homo need not have involved brain enlargement," he noted.

"The more we learn about human evolution, the more we see that traits" that must have happened together could occur separately, Potts said. The study of the hand shows that major changes in the thumb usually associated with stone toolmaking "did not imply abandoning life in the trees. In the foot article, we're introduced to a unique and previously unknown combination of archaic and advanced traits in sediba," Potts explained.

More Australopithecus Sediba Found

facial reconstruction of Australopithecus sediba

Richard Gray wrote in MailOnline: “Since 2010, Professor Berger and his team have unearthed the remains of five other individuals at the Malapa site, including two almost complete skeletons along with a variety of animal fossils. These, he insists, have helped to confirm the attributation of Australopithecus sediba as a unique species. The researchers believe the site was once an ancient cave that perhaps contained a pool of water that attracted a range of animals that fell in. The cave later collapsed, preserving everything down there.[Source: Richard Gray, MailOnline, May 8, 2015 ^=^]

“Professor Berger said he had no idea how many more individuals they may find at the site. Speaking to Naked Scientists said: 'That's why we're building this laboratory over the top that we've begun excavation. 'But so far, what is exposed on the surface have been two main skeletons and at least the remains of 4 other individuals that we found so far. ^=^

But every time we open up a little bit of rock here and move a little bit of dirt, we see someone new. We're introduced to another one of these people that died 2 million years ago. 'The cave is like a big swimming pool that you'd fill up with concrete throwing bones intermediately into it and in this case, some of those and in fact, quite a lot of them, were skeletons of this early human ancestor species.'” ^=^

Australopithecus Sediba Characteristics

The shape of the pelvis, hands and teeths in relatively human-like, but other characteristics are quite ape-like. Professor Berger said: 'They walk on two legs. They would probably only be standing about 1.3 metres tall. They also been more lightly built. They would've been quite skinny. 'They had longer arms than we do, more curved fingers. So, they're clearly climbing something. They also would've moved a little different. Their hips were slightly different than ours and their feet are slightly different. 'So, their gait would've probably been a more rolling type gait, slightly different from the more comfortable long distance stride we had. 'As they got closer to you, you'd be struck by for the most obvious thing which would be, their heads are tiny.' [Source: MailOnline, May 8, 2015]

According to MailOnline: “It has a narrow upper rib cage while the modern human's thorax is uniformly cylindrical. The cone-shaped rib cage allowed the early hominin to move its shoulder blades so it could climb trees. However, this prevented A. sediba from swinging its arms, meaning that walking and running was much more difficult. It had a slim waist similar to modern humans but feet which turned sharply inwards. A. sediba had the same number of lumbar vertebrae as a modern humans and a similar curvature of the lower back. However, its back was longer and more flexible than that of modern humans. They had longer arms than we do with curved fingers, which would have made them adept at climbing. [Source: MailOnline, May 8, 2015]

Earliest Evidence of Cancer Found in Australopithecus Sediba Fossil

In June 2016, an international team of researchers led by scientists from the University of the Witwatersrand's Evolutionary Studies Institute announced in two papers, published in the South African Journal of Science that they had discovered of the oldest evidence for cancer and bony tumours. A University of the Witwatersrand press release said: The discovery of a foot bone dated to approximately 1.7 million years ago from the site of Swartkrans with definitive evidence of malignant cancer, pushes the oldest date for this disease back from recent times into deep prehistory. Although the exact species to which the foot bone belongs is unknown, it is clearly that of a hominin, or bipedal human relative. [Source: Posted by Jonathan Kantrowitz at 1:41 PM No comments: July 2016]

In an accompanying paper appearing in the same journal, a collaborating team of scientists identify the oldest tumour ever found in the human fossil record, a benign neoplasm found in the vertebrae of the well-known Australopithecus sediba child, Karabo from the site of Malapa, and dated to almost two million years in age. The oldest previously demonstrated possible hominin tumour was found in the rib of a Neanderthal and dated to around 120,000 years old.

Edward Odes, a Wits doctoral candidate and lead author of the cancer paper, and co-author on the tumour paper, notes "Modern medicine tends to assume that cancers and tumours in humans are diseases caused by modern lifestyles and environments. Our studies show the origins of these diseases occurred in our ancient relatives millions of years before modern industrial societies existed".

The cancer in a foot bone, a metatarsal, was identified as an osteosarcoma, an aggressive form of cancer which usually affects younger individuals in modern humans, and, if untreated typically results in early death. "Due to its preservation, we don't know whether the single cancerous foot bone belongs to an adult or child, nor whether the cancer caused the death of this individual, but we can tell this would have affected the individuals' ability to walk or run," says Dr Bernhard Zipfel, a Wits scientist and an expert on the foot and locomotion of early human relatives. "In short, it would have been painful."

Lead author of the tumour paper and co-author of the cancer paper, Dr Patrick Randolph-Quinney of Wits University and the University of Central Lancashire in the UK, suggests "The presence of a benign tumour in Australopithecus sediba is fascinating not only because it is found in the back, an extremely rare place for such a disease to manifest in modern humans, but also because it is found in a child. This, in fact, is the first evidence of such a disease in a young individual in the whole of the fossil human record".

Prof. Lee Berger, an author on both papers and leader of the Malapa project where the fossil vertebra was found adds "not only has there been an assumption that these sorts of cancers and tumours are diseases of modernity, which these fossils clearly demonstrate they are not, but that we as modern humans exhibit them as a consequence of living longer, yet this rare tumour is found in a young child. The history of these types of tumours and cancers is clearly more complex than previously thought".

Both incidences of disease were diagnosed using state of the art imaging technologies including those at the European Synchrotron Research Facility in Grenoble, France, medical CT at the Charlotte Maxeke Hospital in Johannesburg, and the micro-CT facility at the Nuclear Energy Corporation of South Africa at Pelindaba.

Australopithecus sediba and the Evolution of Man

Matthew's father Lee

Josh Fischman wrote in National Geographic magazine, “A. sediba's greatest promise may lie in its power to illuminate the murky origins of Homo. The birth of our genus has long been a conundrum for paleoanthropologists, to say the least. Only a few scattered and fragmentary fossils older than two million years have been argued to belong to the genus. Then, around 1.8 million years ago, not one but two or possibly even three Homo species appear, mostly in East Africa. The smaller brained, more primitive ones are called Homo habilis, or "handy man," a name given by Louis Leakey and colleagues in 1964 to specimens from Olduvai Gorge because of their association with the first crude stone tools. Some researchers group a few H. habilis specimens into a separate species, Homo rudolfensis. Then there is Homo erectus (the early African forms are sometimes called Homo ergaster) — larger brained, bigger bodied, more advanced, yet contemporaneous with little H. habilis. [Source: Josh Fischman, National Geographic , August 2011]

Where did all these characters come from? Attempts to look deeper into the past only increase the frustration, says William Kimbel, a paleoanthropologist at Arizona State University and director of the Institute of Human Origins there. "There are only a handful of specimens. You could put them all into a small shoe box and still have room for a good pair of shoes," he says. An upper jaw from Hadar in Ethiopia, found by Kimbel himself, is 2.3 million years old. A lower jaw from Malawi may be 100,000 years older, though the dating is uncertain. Some researchers would include a skull piece from Kenya of about the same age. That's about it.

Enter the skeletons of A. sediba — as resplendently well preserved as those shoe box fossils are not. Anatomically, the species shows a mix of primitive and advanced traits. In addition to its long upper limbs, small brains, and primitive heel bone, its small body size and the shape of its molar cusps and cheekbones hark back to earlier australopiths, such as A. africanus, that lived in southern Africa between two and three million years ago. (Indeed, some researchers suggest that it might be a late form of that species.) The long legs and that modern ankle are key elements on the human side of the ledger, says Darryl de Ruiter, a paleoanthropologist at Texas A&M University and part of the Malapa team. He also cites the surprisingly humanlike pelvis built for a fully bipedal stride; smaller teeth and chewing muscles; a projecting nose and some other features of the face; and that remarkable, precision-grip hand. These traits are enough for the team to propose it as the australopith species most likely to have given rise to Homo.

But which Homo? The team leans very cautiously toward Homo erectus, the species generally seen as the immediate forerunner of Homo sapiens. If this is so, then the smaller, mostly East African forms now attributed to Homo, including Louis Leakey's original toolmaker H. habilis, would become a branch of the family tree that simply petered out. It is not the first time scientists have suggested these species could be evolutionary dead ends. But the Malapa fossils bring more clout to the debate. "Sediba casts everything called Homo before erectus into question," says de Ruiter.

The biggest obstacle facing this challenge to the establishment view is the timing. If two-million-year-old A. sediba is indeed the true ancestor of Homo, how could it give rise to those even older fossils assigned to Homo in Bill Kimbel's shoe box? A fossil cannot be ancestral to something older than itself any more than a daughter can give birth to her own mother. One possibility is that the Malapa specimens represent a late stage of an enduring species that gave rise to Homo at an earlier date. But Berger's team questions whether that shoe box really contains any Homo fossils in the first place — after all, they're just fragments. Kimbel doesn't buy it.

"It's nonsensical to dismiss fragments, because fragments do tell you something," he says. He points out that the upper jaw from Hadar has a short, broad, humanlike dental arch and flat snout, placing it firmly in the Homo genus — and it is at least 300,000 years older than A. sediba. Berger's team, however, insists that Malapa changes the game. Articulated skeletons are far more than the sum of their parts: They prove that parts in isolation can be misleading. Think of the bits of A. sediba that look primitive, and the other bits that look modern, he says. The Hadar jaw, in the same way, might not accurately represent the rest of the creature.

"How can the Hadar jaw be misleading?" says Kimbel. "Either it shares features with later Homo, or it does not. Nothing in sediba can change that." If the Hadar jaw really is Homo, says Berger, then perhaps its dating is wrong — a contention Kimbel disputes as vigorously as he supports the validity of his fossil.

The truth about A. sediba's place in our ancestry may still be lying in the ground. "The beauty of a place like Malapa is that there are many more bones, and more individuals to come," Berger says. Ultimately the fossils, not the arguments, will carry the day.

Australopithecus Sediba; A Modern Human Ancestor?

Scientists are still attempting to piece together exactly how Australopithecus sediba fit into the evolutionary history of humans. The age of the skeletons and their mix of traits has Lee Berger of the University of the Witwatersrand and his colleagues to theorize that Australopithecus sediba may be a direct ancestor of our genus, Homo. However, the discovery has been controversial.

On the impact of Fossils found in Dmanisi, Georgia and dated to 1.8 million years ago that suggests that half a dozen species of early human ancestor were actually all Homo erectus, Ian Sample wrote in The Guardian: The finding casts doubt on claims that Australopithecus sediba was a direct ancestor of modern humans. Berger argued that it was premature to dismiss his finding and criticised the authors for failing to compare their fossils with the remains of A sediba. "This is a fantastic and important discovery, but I don't think the evidence they have lives up to this broad claim they are making. They say this falsifies that Australopithecus sediba is the ancestor of Homo. The very simple response is, no it doesn't. What all this screams out for is more and better specimens. We need skeletons, more complete material, so we can look at them from head to toe," he added. "Any time a scientist says 'we've got this figured out' they are probably wrong. It's not the end of the story." |=| [Source: Ian Sample, The Guardian, October 17, 2013]

Malapa Caves: Australopithecus sediba Discovery Site

Describing the site where the Australopithecus sediba fossils were found, Josh Fischman wrote in National Geographic magazine, “It is a hole in the ground about 25 miles northwest of Johannesburg, in a ridged brown valley where herds of giraffes occasionally parade between stands of trees. The red-rock walls of the pit are higher than Berger's head, and steep enough in spots to make a scramble up, or down, rather daunting. Some two million years ago, the hole was a great deal deeper, with no possibility of escape for any creature that fell in. This accounts for the trove of fossils Berger is finding, which in turn accounts for his upbeat mood. He leans over a red boulder near the pit bottom, tracing a white-colored protrusion with his fingers. "It looks like part of an arm," he says. "That means we've found another individual." [Source: Josh Fischman, National Geographic , August 2011]

The first two skeletons removed from the pit were a young adolescent male, 12 or 13 years old, and an adult female... The site, an eroded limestone cave called Malapa, is in a region already so famous for its ancient human fossils that it is often referred to as the Cradle of Humankind. Much of that reputation rests on finds from the early 1900s, back when South Africa harbored the best evidence for early human evolution, including Australopithecus africanus, at the time our oldest known ancestor. Beginning in the late 1950s, the epochal finds of the Leakey family in Tanzania and Kenya, followed later by Donald Johanson's celebrated discovery of the 3.2-million-year-old Lucy skeleton in Ethiopia, shifted cradle-bragging rights to East Africa, where they have remained ever since. Lee Berger thinks the cradle is about to rock again. He believes Malapa may hold the key to one of the most significant, least understood chapters in the human evolutionary journey: the origin of the first species enough like us to be called human — a member of the genus Homo. "This is where that story may have begun," he says, as he starts the climb out of the pit.

The age of the fossils was determined by dating the calcified sediments surrounding them with advanced uranium-lead dating techniques and a method called paleomagnetic dating, which measures how many times the Earth's magnetic field has reversed. They discovered the fossils were approximately 1.977 million years old, which predates the earliest appearances of traits specific to the human lineage Homo in the fossil record. This places Au. sediba in roughly the same age category as hominins such as Homo habilis and Homo rudolfensis, which were thought to be potential ancestors to Homo erectus, the earliest undisputed predecessor of modern humans.

Malapa Caves: A Water Source for Australopithecus sediba

Malapa

Josh Fischman wrote in National Geographic magazine, “The abundance and spectacular condition of the fossils have much to do with the peculiar geography of the place. Malapa, it seems, was both a water source that gave life and a trap that snuffed it out. Two million years ago, a cave-studded aquifer lay beneath an undulating plain of shallow, wooded valleys and rolling hills. Some of the caves were open to the surface through steep entryways or vertical shafts stretching up to 160 feet. In wet periods, when the water table was high, animals could easily drink from seepage ponds near the surface. During drier times they would venture into the darkness of a hole, following the sound or scent of water — and risking a plunge down a hidden shaft. (The boy's upper arm bones show fractures typical of a headfirst fall from a great height.) [Source: Josh Fischman, National Geographic , August 2011]

"These animals had no choice. They needed water to survive," says Brian Kuhn, a zoologist from the Johannesburg university — called Wits for short — who works at the Malapa site. After death, their bodies would wash down even deeper in the cave system, becoming entombed within days or weeks in a single, thick layer of sand and clay, rather than a succession of thin layers, as would have happened had the sediments accumulated over months or years.

This raises the possibility, says Berger, that all the hominins — at least four are now known from the site — died weeks or even days apart, and therefore may have known each other in life. The rapid burial also caused their flesh to take longer to decompose, packaging the skeletons in death as they were arranged in life, right down to tiny bones of the hands and feet. Indeed, the rapid entombment may have preserved some of the skin itself, on top of the boy's skull and on the woman's jaw near the chin’something never before seen in a hominin fossil.

"Wow!" says Nina Jablonski, an anthropologist at Pennsylvania State University and author of the book, Skin: A Natural History. "The possibility of preserved australopithecine skin is massively cool." What makes it so cool is the possibility of determining how these near humans reacted to heat. She is particularly interested in whether the alleged skin (or a fossilized impression of the skin, if that's what it is) might contain evidence of scalp and facial hair, and a high density of sweat glands.

Jablonski thinks such glands could be a precondition to the bigger brains long seen as a defining attribute of Homo. Chimpanzees, our closest living relatives, spend most of their time sheltered from the sun's heat by forest cover and have a limited ability to sweat. Our earliest ancestors also typically occupied woodland environments. But as the environment became drier around two million years ago, they began to forage in more-open grasslands — a problem for brains, which are notoriously vulnerable to heat. Bigger brains require even more cooling. A marked increase in the number of sweat glands and a reduction in body hair could have provided that, Jablonski speculates, in turn allowing for further brain growth as Homo began to use those bigger brains for toolmaking, planning, and other cognitively challenging activities.

Image Sources: Wikimedia Commons

Text Sources: National Geographic, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Nature, Scientific American. Live Science, Discover magazine, Discovery News, Times of London, Natural History magazine, Archaeology magazine, The New Yorker, Time, Newsweek, BBC, The Guardian, Reuters, AP, AFP and various books and other publications.

Last updated April 2024