Team hopes find will tell human story

Researchers hope a rare fossil can help explain the growth of earliest humanity.
CLEVELAND (AP) -- In the eight decades or so that fossil hunters have roamed nature's graveyards in search of the earliest traces of humanity, the pickings have been mighty slim.
Wind, water and predators scoured the African bush with a cruel efficiency long before the first scientists arrived. They didn't leave much -- a cracked molar here, a flake of thigh bone there.
So when veteran searcher Alemayehu Asfaw unearthed a weathered shank of forearm a month ago in the hilly Ethiopian badlands south of the Mille River, there was no reason to think anything extraordinary would follow. The rest of the fossil-hunting team, led by paleoanthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History, had turned up only old monkey and antelope bones and was ready to move on.
But they dropped to hands and knees out of habit to crawl the dusty plot, hoping to locate other pieces of the fossilized arm bone.
What they found instead, in rapid succession, was a veritable anatomy lesson: parts of upper arm and leg bones, ribs, stubby vertebrae, the lacy swirl of sacral bones that sit atop the pelvis. All 50 or 60 specimens found that day were lying on the surface or captured in the mesh sieves that workers used to sift the top layer of dirt.
The searchers planted yellow plastic flags to mark each fossil's location. Soon, the excavation site looked as if a patch of daffodils had sprouted from the parched earth.
When dwindling money and supplies ended the expedition earlier this month, the Cleveland team had achieved one of anthropology's rarest feats -- recovering the partial skeleton of an early human ancestor. They located more than 400 bones and bone fragments, and suspect others are still buried in the hard-packed ground, waiting to be exhumed when digging resumes next year.
"We have neck bones, we have ribs, a partial upper leg, a scapula, just on the surface," said museum director and expedition co-leader Bruce Latimer, in his and Haile-Selassie's first interview since returning to Cleveland. "Just the elements we've found so far are indicative we're going to find more."
Fifth found
Only four other relatively intact skeletons older than 1 million years have ever been found.
The most famous of those -- but not the most complete -- is "Lucy," the 3.2-million-year-old Australopithecus afarensis specimen found in 1974 by Donald Johanson, at the time the Cleveland museum's curator of physical anthropology.
Compared with a full 206-bone skeleton, Lucy is 20 percent intact.
The other partial skeletons are the 4.4 million-year-old bones of a primitive ape-man called Ardipithecus ramidus that Haile-Selassie helped uncover in Ethiopia in 1994; an extraordinarily intact skeleton of a 1.6 million-year-old Homo erectus youth nicknamed Turkana Boy that Pennsylvania State University paleontologist Alan Walker and colleagues identified in Kenya in 1985; and a nearly complete but unclassified skeleton, approximately 4 million years old, still embedded in a cave wall in Sterkfontein, South Africa.
The Cleveland team's bones are in much better shape, though they still must be cleaned and the jigsaw fragments reassembled as much as possible. The fossils will stay in Ethiopia's National Museum. Latimer, Haile-Selassie and other researchers will study plaster copies.
4 million years old
Judging from the types of animal fossils recovered nearby, the partial skeleton is about 4 million years old. Scientists should be able to pin down the fossils' exact age by measuring the rate of radioactive decay of volcanic rocks that surrounded them.
Haile-Selassie and Latimer immediately knew by looking at the fossilized lower leg bone, or tibia, that their creature walked on two legs. The surface where the tibia rested on the ankle was flat, indicating the leg was aligned from hip to foot. Apes and monkeys, which move on all fours, are knock-kneed and have angled tibial joints.
But determining which early human species the remains belong to will be more difficult, especially if the team can't find the skull, jaws or teeth.
Those have distinctive features -- especially the size and wear patterns of teeth -- that researchers can compare with existing fossil collections, looking for similarities and differences.
Jaws and teeth are dense and fairly durable. More fragile bones don't often survive the ravages of time. Shoulder blades, for example, are as thin and translucent as a Wedgewood plate. Vertebrae are crunchy, fat-filled morsels, a perfect snack for hyenas.
That the team has found a shoulder blade and six neck vertebrae in good shape gives them reason to hope. "If everything works out right, the head should be there," Haile-Selassie said.
Link to Lucy
Even without the cranium, the Cleveland researchers have a trove of body parts to analyze and compare with older and younger fossil specimens. A 4-million-year-old skeleton, whatever species it turns out to be, fits perfectly in the evolutionary gap between the primitive Ar. ramidus skeleton and the relatively modern A. afarensis.
"We can work from the ramidus skeleton, through this, to Lucy," said Latimer. "We can actually start to tease out when the changes occurred, because they didn't all occur at the same time. When did the knee change, and the ankle and the back? With a skeleton, you can ask those questions."
Though Haile-Selassie and Latimer are veteran fossil-hunters, this is the first season they've run their own expedition. The logistics of transporting, feeding and sheltering nearly two dozen people for weeks in the harsh African bush is akin to a military operation.
On the last night in the desert, after stacking big rocks over the fossil site to protect it until next January, some of the team members gathered for a small, quiet celebration.
It was nothing like Johanson's long-ago party for Lucy, where a boozy reveler jamming to a Beatles song decided its title character's name fit the presumably female fossil.
There would be no nickname for the Clevelanders' skeleton, just a simple specimen number, KSD-VP-1/1. Latimer cracked open a canteen of bourbon, and he and Haile-Selassie stayed up until dawn, talking about what might still lie under the Ethiopian sands.