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New species in human lineage's evolution discovered

By David Brown
Washington Post Staff Writer
Friday, April 9, 2010; A02

Researchers have discovered in South Africa two partial skeletons of a new species of evolving primate that incorporates ape and human features in a previously unseen combination.

The skeletons, of a boy and a young woman, have orangutan-length arms but human-shaped hands. Changes to the legs and pelvis suggest that the creatures spent much of their time upright, although their feet are primitive. They have small, humanlike teeth but an ape-size braincase.

Although anthropologists long ago rejected the notion of a missing link in human prehistory waiting to be found, few doubt that there are "missing strands" in the tangled braid of co-evolving pre-human lineages.

The new species, named Australopithecus sediba, appears to be one of them. Whether it led to the final, successful strand, Homo sapiens, or died out is not known. Either way, the discovery is likely to shed light on a key transition in which pre-human primates took to the ground, eventually acquiring modern appearance and behavior.

"What this shows us is something very surprising," said the skeletons' discoverer, Lee R. Berger of the University of Witwatersrand in South Africa. "Sediba is becoming a terrestrial biped first but is almost maintaining a sort of reserve parachute in having very long apelike arms. . . . The face is beginning to show [more modern] characters, and yet it sits with this remarkably small brain."

The discovery has attracted attention for other reasons, too.

Berger said that Google Earth helped him recognize a series of unexplored caves along a geologic fault northeast of Johannesburg and that the Internet application "is really the reason I could make this discovery." The first bone found -- the collarbone of the child -- was spotted by Berger's 9-year-old son, Matthew, in the remains of a collapsed cave called Malapa, now eroded to the surface.

Other researchers agreed that Australopithecus sediba -- "sediba" means "wellspring" in the Sotho language spoken in the Malapa area -- is an unusual addition to the family tree.

The remains "definitely show that it has a constellation of features that is different from anything else to date," said Rick Potts, director of the human origins program at the Smithsonian Institution's National Museum of Natural History. "What we don't know is how ephemeral or how persistent that combination of features was," he added.

"The South African finds from Malapa are most interesting," said Donald Johanson, an anthropologist at the University of Arizona and co-discoverer of "Lucy," the famed 3.2 million-year-old skeleton found in Ethiopia in 1974.

The Malapa skeletons were found in 2008. At least two more have been found since, Berger told reporters in a telephone briefing, although he did not give details. Work is underway to reconstruct what Australopithecus sediba, standing a few inches over four feet, looked like, he said, adding that his colleagues are also drawing inferences about some of its behavior.

The discovery is already contributing to the taxonomic arguments so common in anthropology.

The finders say it is a transitional species between Australopithecus africanus and the many species in the more modern genus Homo. They think it could be a direct ancestor of Homo habilis ("handy man"), whose remains are sometimes found with crude stone tools.

Johanson has examined the fossils and says they clearly belong in Homo. Potts argues that similar skeletons need to be found at another site, and preferably from a different time, to be certain they represent a new species at all and not just a chance combination of physical traits in a family group of an existing one.

The find consists of the skull and much of the lower jaw of the boy but only the lower jaw of the woman, who was possibly in her late 20s or early 30s. Each skeleton also contains substantial portions of the right arm, parts of the right leg and foot, and some key parts of the pelvis.

The bones are 1.95 million to 1.78 million years old, from one of the "most poorly represented" periods in the fossil record, Berger said.

The skeletons were found packed in concrete-like material at the bottom of what was once a cave 150 feet below ground. Nearby were fossils of a saber-toothed cat, antelopes, mice and rabbits. No bones showed any signs of having been chewed or disturbed by scavengers.

"We think there must have been some sort of calamity taking place that caused these fossils to be deposited," said Paul H. G. M. Dirks of James Cook University in Australia, who headed the geological analysis of the Malapa site.

The best guess is that both individuals fell to their deaths. Soon, a rainstorm swept their bodies to a deeper, dead-end passage. Sand and gravel then packed them solid.

Whether the individuals were mother and child and whether they fell at the same time is unknown. "They probably would have been territorial, part of the same troop," Berger said.

The first bones were found Aug. 15, 2008, when Berger visited the Malapa site for the second time. His son, his dog and a postdoctoral student accompanied him. He suggested that they look for fossils, and within a minute and a half, Matthew announced, "Dad, I found a fossil!"

"Five meters away from him, I realized he had a hominid clavicle sticking out of the rock," Berger said. "I did my PhD on them, and they are very easy to recognize."

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