Australopithecus sediba: The Malapa Fossils Found by a Boy

Australopithecus sediba is an extinct hominin species known from fossils found at Malapa, a collapsed cave in South Africa’s Cradle of Humankind, and dated to about 1.98 million years ago. The first bone was spotted in August 2008 by nine-year-old Matthew Berger. The species, named in 2010, combines a small brain and climbing arms with surprisingly human-like hands, teeth and pelvis, which made it a key, and much debated, piece in the puzzle of where the genus Homo came from.

Background: the Cradle of Humankind

The dolomite hills north-west of Johannesburg contain dozens of ancient caves filled with bone-bearing sediment. Since the 1930s, sites such as Sterkfontein, Swartkrans and Kromdraai have produced many fossils of australopiths and early Homo, including the skeleton known as Little Foot. In 1999 the area was listed by UNESCO as a World Heritage Site, the Fossil Hominid Sites of South Africa.

In 2008 the American-born palaeoanthropologist Lee Berger of the University of the Witwatersrand began mapping cave sites in the region using satellite imagery and Google Earth. He identified hundreds of possible new caves, among them a site near the Malapa farm, about 15 kilometres north-east of Sterkfontein.

The discovery in 2008

On 15 August 2008 Berger visited Malapa with his son Matthew and the Kenyan researcher Job Kibii. Matthew wandered off with the family dog and soon called his father over to a rock he had found. Embedded in it was a hominin collarbone, and on the same block Berger recognised part of a lower jaw.

Excavation soon revealed two partial skeletons. MH1, a juvenile male, was probably around 12 to 13 years old by modern human standards, though the species likely grew faster than we do. MH2 was an adult female. Later work recovered remains of further individuals, including an infant. The bodies seem to have fallen into a deep cave shaft and been rapidly buried, which helped preserve them.

A mosaic of features

The species was announced by Berger and colleagues in the journal Science in April 2010. Its anatomy is a striking mix. The brain of MH1 was small, about 420 cubic centimetres, similar to other australopiths. The arms were long and the shoulders adapted for climbing.

Other parts look more like Homo. The cheek teeth are relatively small, the face less projecting, and the hand has a long thumb and short fingers suited to a precision grip. The pelvis has a broad, human-like shape. The foot and ankle combine a primitive heel with a more human ankle joint, suggesting an unusual way of walking that may have involved turning the foot inward.

Dating and debate

In 2011 a team led by Robyn Pickering used uranium-lead dating of flowstone layers to date the fossils to about 1.977 million years ago, one of the most precise dates for any early hominin. That timing, close to the appearance of early Homo, encouraged Berger’s team to propose that Australopithecus sediba, or something like it, could be ancestral to our genus.

Many researchers disagree. A jaw from Ledi-Geraru in Ethiopia assigned to Homo is about 2.8 million years old, much older than Malapa, and early Homo fossils from East Africa also predate sediba. Critics therefore see it as a late-surviving relative that evolved human-like traits independently, or as a descendant of a population close to the origin of Homo rather than the ancestor itself. Its relationship to Homo habilis and other early Homo remains an open question.

Life at Malapa

The Malapa deposits also preserve the bones of other animals, including antelopes, carnivores such as sabre-toothed cats, hyenas, horses, mice and birds. Together they suggest a landscape of grassland and woodland around a cave with a deep vertical shaft, perhaps attractive because water collected in it.

Studies of tartar on the teeth of MH1 and MH2, published in 2012, recovered tiny plant particles called phytoliths. Combined with chemical analysis of the enamel, they suggest that Australopithecus sediba ate mainly forest foods such as leaves, fruit and bark, unlike some other hominins of the time that relied more on grasses and sedges.

By the numbers

Legacy

Malapa set a new standard for openness. The fossils were made available to many researchers, and casts and scans were widely shared. Berger and colleagues went on to the discovery of Homo naledi in the nearby Rising Star Cave in 2013, which drew on the same approach.

Timeline

• c. 1.977 million years ago: Hominins at Malapa fall into the cave and are buried.
• 2008, August: Lee Berger identifies the Malapa site during his cave survey.
• 2008, 15 August: Matthew Berger finds the collarbone of MH1.
• 2010, April: The species Australopithecus sediba is announced in Science.
• 2011, September: Detailed studies of the hand, foot, pelvis, brain and dating appear in Science.

Why it matters

Australopithecus sediba showed that hominins around two million years ago combined old and new features in unexpected ways. Whether or not it lies on the human line, it shows that human-like hands, teeth and hips did not evolve together as a single package.