A dig started by an ASU researcher in Ethiopia almost six years ago has unveiled a major discovery, scientists say.
Dr. Zeresenay Alemseged, a former ASU paleoanthropologist, announced last week that he and his team have discovered the oldest, most complete skeleton of a juvenile human ancestor in Dikika, Ethiopia.
ASU Institute of Human Origins professor William Kimbel, a member of Zerensenay's team, said it was a "jaw-dropping" experience the first time he saw the fossils in Ethiopia.
"I was speechless," he said. "You can hardly imagine the preservation."
The 3.3-million-year-old skeleton is that of a 3-year-old Australopithecus afarensis child, a species with many similarities to primates as well as humans.
The skeleton is the same species as Lucy, the 3.18-million-year-old female skeleton found by IHO director Donald Johanson in the same area of Ethiopia in 1974.
Nicknamed "Lucy's baby" by some, the fossil's name is Selam, which means "peace" in Amharic.
The discovery is significant, Kimbel said, because it's the oldest juvenile skeleton ever found, and because certain parts of the fossils can point to conclusions about human development.
For example, he said, Selam's skull was preserved in the hard sandstone that encased the skeleton.
From that fossil, the team was able to estimate Selam's brain capacity at 330 cubic centimeters, a size comparable to that of an ape.
A CT scan of the jawbones revealed Selam's teeth were at a stage of development equivalent to a 3-year-old of her species. By evaluating the size of her canine teeth, the researchers were also able to determine Selam's sex as female.
As in apes, A. afarensis specimens typically have large canines if male and smaller canines if female, Kimbel said. Selam had small canines.
Johanson said the team will also look at the layers of enamel on Selam's teeth and compare that data to Lucy. The team may even be able to pinpoint Lucy's age in years, whereas before, researchers could only determine she was an adult.
Selam's well-preserved shoulder blades are another remarkable feature of her skeleton, Kimbel said.
Those bones are very thin, and often don't survive millions of years of erosion, Kimbel said.
But Selam's shoulder blades did survive, and look very similar to those of a gorilla, Kimbel said.
This discovery stirs debate among paleoanthropologists, he said, because Selam's other features including her thighbone, shinbone and foot clearly indicate the girl walked upright.
The shoulder blades, as well as Selam's long fingers, may indicate A. afarensis preserved its capability for tree climbing.
On the other hand, these bones may have just been remnants of an earlier stage in evolution, that were on their way to being adapted toward more human-like features, Kimbel said.
These unanswerable questions show more research needs to be done, he said.
Alemseged has been carefully excavating and preserving the skeleton using dental tools since he was a researcher at ASU in 2000.
Even after six years of stripping the skeleton grain-by-grain of its surrounding sandstone cast, there is still more of the skeleton that hasn't been revealed.
"So much more still needs to be done," Johanson said. "This will allow us to establish a sequence of events in terms of how we have changed over the millennia."
Reach the reporter at: annalyn.censky@asu.edu.
