New Fossil May be ‘Missing Link’ in Human Evolution

Scientists in South Africa have discovered a key missing link in human evolution - a hominid 1.8 million-years-old that may be the oldest direct human ancestor ever found.

The fossils of the species, dubbed Australopithecus sediba, were among an extensive collection found in newly-exposed cave sediments at the Malapa Cave site, about 28 miles northwest of Johannesburg. They are the most complete early hominid fossils ever found.

The finds shed light on a sparsely documented era of evolution when four or more ape-like hominid species lived in Africa.

Because the skeletons are nearly complete, scientists can relate the face to the hand, the body, and the brain of a single individual. Consequently, this is the most complete hominid skeletons we have until the Neanderthals.

According to the in depth study published in the journal Science, while the tiny skulls, long arms, and diminutive bodies were all quite chimp-like, the ankles, hands, and pelvis were surprisingly modern.

Reconstructing the creature's grapefruit-sized brain based on three-dimensional X-ray scans of a fossilized cranium, scientists claim that the early hominid also showed some of the first signs of sophisticated mental abilities.

About 4 feet tall, the fossils of Australopithecus sediba (southern wellspring ape) were discovered in 2008 and first reported last year. The vanished species climbed trees like orangutans and walked on the ground like people.

Here's a quick look at the early hominid's human-like features as revealed in the fossil find:

-Foot bones reveal an upright-walking stance, while ankle bones show a tree-climber.

-Fossil hands reveal long thumbs and wrists similar to modern humans that would enable the use of tools. However, curved fingers appear more ape-like.

-While the brain was less than one-third the size of modern human's, features in the inner skull suggest specialized brain areas found in modern humans.

-Pelvis reconstructions reveal broad hips that the team argues allowed these human ancestors to birth large-brained babies.

The team of 80 scientists and technicians, led by Lee Berger of the University of Witwatersrand in Johannesburg, claim that the species was likely the ancestor of the genus Homo, to which all modern humans belong.

However, this claim has been disputed by several researchers in the field who argue that the species was more likely an evolutionary dead end.

Just because it shares a bit of anatomical morphology with Homo does not mean it is Homo or ancestral to Homo, anthropologist Bernard Wood at George Washington University told The Wall Street Journal. It looks increasingly that these bits of morphology are appearing more than once, independently, in the tree of life.

Yet, Wood acknowledges that the bones are stunning and challenge several assumptions about human origins.

So far Dr. Berger and his team have discovered 220 bones comprising the skeletons of five individuals. Remarkably, these include infant, juvenile and adult remains representing both sexes. The collection may be of a family that died by falling into the Malapa Cave roughly 1.98 million years ago, based on laboratory estimates. Some bones were found still connected to each other as they may have been when they died.

Scientists will likely debate for several years whether Australopithecus sediba is a missing link or a dead end. Either way, the find provides a treasure trove of knowledge on early hominids.