By Rob Stein
Washington Post Staff Writer
Thursday, September 21, 2006; A01
Fossil hunters have unearthed the skeleton of a young girl who died 3.3 million years ago, marking the first time scientists have discovered the nearly complete remains of a child of an ancient human ancestor.
The girl, who was about 3 years old when she perished in what may have been a flash flood, provides an unprecedented window into human evolution, in part because she belongs to the same species as "Lucy," one of the most famous hominid specimens in paleontology, experts said.
That prompted some scientists to refer to the new skeleton as "Lucy's baby," even though they estimate that the child lived about 150,000 years earlier. The researchers who discovered her in an Ethiopian desert named her Selam, which means "peace" in several Ethiopian languages.
Although scientists have found bones and bone fragments of children from this and other species of human predecessors, and a few skeletons, the discovery represents one of the most complete individuals ever recovered and by far the oldest. Bones of young children are so small and soft that few survive.
"I'm very excited," said Zeresenay Alemseged of the Max Planck Institute in Leipzig, Germany, who led the international team reporting the find in today's issue of the journal Nature. "This is a unique discovery in the history of paleoanthropology."
Independent experts agreed, saying the discovery probably would lead to important insights into humans' evolutionary history.
"It's just an amazingly complete specimen," said Bernard Wood of George Washington University, who wrote an article accompanying the paper. "I have to keep picking up the photograph of it to make sure I didn't dream it."
Scientists are still painstakingly extracting the fossilized bones from the surrounding stone, but they have already made striking discoveries, dramatically reinforcing the idea that the creatures were a transitional stage between apes and humans. Although they had legs like humans that enabled them to walk upright on two feet, they also had shoulders like gorillas that may have enabled them to climb trees; although their teeth seem to have grown quickly, like chimps' teeth, their brains may have matured more slowly, like those of humans.
"This confirms the idea that human evolution was not some straight line going from ape to human," said Rick Potts of the Smithsonian Institution. "The more we discover, the more we realize that different parts evolve at different times, and some of these experiments of early evolution had a combination of humanlike and apelike features."
The child's species, Australopithecus afarensis , lived between about 3.8 million and 3 million years ago and is among the earliest known forerunners of modern humans. It has long played an important role for scientists studying evolution, in part because of the well-preserved remains of Lucy, an adult discovered nearby in 1974.
The youngster's fossilized remains, the first to fully exhibit the mixed ape-human characteristics in a child, were found in the remote, harsh Dikika area of northeastern Ethiopia in 2000 when an expedition member spotted the face of the skull poking out from a steep dusty hillside. The surroundings indicate that the child might have drowned in a flash flood, which immediately buried the intact remains in sand that hardened to encase the bones, the researchers said.
Over the next four years, researchers slowly recovered much of the rest of the child's skeleton, including the entire skull, with a sandstone impression of the brain, jaws with teeth, parts of the shoulder blades and collarbone, ribs, the spinal column, the right arm, fingers, legs and almost a complete left foot.
National Geographic magazine provided some of the funding for the project.
Until now, the only fairly complete skeletons of young children in the human evolutionary tree found by scientists were those of modern humans and Neanderthals, which date back only about 60,000 years.
"We've never had anything so complete before," said Donald C. Johanson of Arizona State University, who discovered Lucy. "This is going to allow us to have extraordinary insight into the growth and development of this species."
Zeresenay has been painstakingly etching away the sandstone, almost grain by grain, with a dentist's drill to protect the tiny vertebrae, ribs and other bones. One finger is still curled in a tiny grasp. High-tech scans of the teeth enabled researchers to identify the child's sex and approximate age.
Where the child's throat once was, Zeresenay found a hyoid bone, which is located in the voice box and supports muscles of the tongue and throat. It is the first time that bone has been discovered in such an old fossil of a human predecessor. It appears more primitive than a human hyoid and more like those in apes, suggesting that the 1 1/2 -foot toddler sounded more like a chimp than a human.
"If you imagine how this child would have sounded if it was crying out for its mother, its cry would appeal more to chimp ears than to human ears," said Fred Spoor of University College London, who is helping to study the remains. "Even though it's a very early human ancestor, she would sound more apelike than humanlike."
The child's lower limbs confirm earlier findings that the species walked upright like humans. But the shoulder blades resemble a young gorilla's. Along with the long arms, curved fingers and inner-ear cavity, the bones provide new evidence supporting those who believe the creatures may have still climbed trees as well.
"I see this species as foraging bipeds -- walking on two feet but climbing trees when necessary, such as to forage for food," Zeresenay said, adding that more research will be needed to be certain of that controversial conclusion.
The skeleton offers scientists the first opportunity to examine various parts of the body in a single specimen rather than looking at individual bones from different representatives.
"Before this, you didn't know if it was like you might have the arm of a Danny DeVito and the leg of a Kareem Abdul-Jabbar," Potts said.
The discovery of a child also allows scientists to begin to study how the species developed. The child's brain size suggests that the species' brain matured relatively slowly.
"If the brain was developing slower, as in humans or similar to what you see in humans, here might have also been the beginnings of behavioral shifts towards being more human," Zeresenay said.