Deepening the mystery of human origins, researchers Thursday offered the most complete view yet of fossils from a puzzling forerunner of humankind, revealing that these creatures were, from head to heel, a collage of primitive and modern anatomy.
In six research papers published in Science, an international team described how the hominids had almost-human hands attached to apelike arms, a rib cage that was narrow like an ape’s at the top but more humanlike lower down, and a spine that likely had the same number of vertebrae as a human.
Fossils from this ancient offshoot of the human family tree, called Australopithecus sediba, were discovered in 2008 at Malapa, near Johannesburg, South Africa.
These curious hominids lived about two million years ago in an era that scientists consider the crucible of human evolution, when four or more apelike hominid species struggled for survival in Africa. The new in-depth analysis of their remains highlights the fits and starts of evolution’s early advances in intelligence and mobility, several independent experts said.
“It is hugely significant,” said paleoanthropologist Ian Tattersall of the American Museum of Natural History in New York, who wasn’t involved in the work. “This is a good example of what we see throughout the human fossil record—vigorous experimentation with species thrown out to succeed or fail.”
Taken together, the research, led by Lee Berger of South Africa’s University of the Witwatersrand, comprises a detailed forensic autopsy on what may be the ultimate cold case: what became of six or more of the sediba species that apparently fell to their deaths in the Malapa Cave about 1.97 million years ago. No one knows if they died together or alone. There is no evidence the creatures were killed by animals.
The sediba fossils encompass the most extensive set of early prehuman remains ever found, the scientists said. So far, they have identified partial skeletons of a male, a female and a juvenile, and remains of several infants of the species, preserved in some instances right down to traces of tartar clinging to their teeth.
“Almost every bone or every area of anatomy is the most complete of its kind ever found in the early hominid record,” said Dr. Berger. “You end up with this really mosaic combination of ape and humanlike in a way we would have never predicted.”
The analysis by 26 scientists at 16 institutions world-wide involves three of those skeletons. It documents sediba as a creature that stood barely chest-high to a modern human. It had narrow apelike shoulders and long dangling arms suitable for climbing trees, yet its hands were delicate, with fingers readily capable of making and holding tools. Its rib cage was narrow like an ape’s at the top but broader and almost human lower down.
“To me, this is exactly what Darwin’s theory predicted should exist,” said paleoanthropologist Darryl de Ruiter at Texas A&M University who studied its teeth and jaw. “It is something that has characteristics of its ancestors and of its descendants.”
Fossils of its leg, knee and foot bones suggest it walked upright, but in an unusual shuffling gait all its own, rolling on the outside of its foot with each step, the researchers said.
“This is not anything that is going to run a marathon,” said biological anthropologist Jeremy DeSilva at Boston University who analyzed its likely walk. “They probably took rapid short strides from one patch of trees to the next.”
Marshaling the evidence of sediba’s teeth, the researchers said their findings cemented its status as a distinct species in its own right. They compared the sediba crowns, molars and incisors to those from eight other prehuman species and also to gorillas.
But the researchers acknowledged that they failed to prove the species is the direct ancestor of humankind.
“The jury is out on the claim that it is an ancestor of the kind that gave rise to the genus Homo,” which includes modern humankind, said Rick Potts, director of the human-origins program at the Smithsonian National Museum of Natural History in Washington, who wasn’t involved in the research. “It is such an amalgam: It climbed trees, walked on the ground, likely used tools and might have been a dead end.”
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