In a paper published today in Nature, paleoanthropologist Zeresenay Alemseged of the Max-Planck-Institute for Evolutionary Anthropology in Leipzig, Germany, and his colleagues unveil the remarkable skeleton of an Australopithecus afarensis child who lived 3.3 million year ago. Scientific American.com editorial director Kate Wong called Alemseged at his office to talk about the discovery. An edited transcript of their conversation follows.
KATE WONG: How did you come to work in this part of Ethiopia?
ZERESENAY ALEMSEGED: The area is called Dikika, which actually means "pointed hill" or "nipples." It's a hill which is not far from the spot where we found the hominid. I started the project back in 1999, just after I finished my Ph.D. in Paris in 1998. This site is surrounded by many famous [hominin] sites, such as Hadar, Gona, the Midle Awash and others. It basically belongs to the same sedimentary basin, so I was not surprised that it yielded hominins. This site was actually found in the 1970s, along with the other sites. But it was not until 1999 that there was an expedition to this place, which I led.
When I decided to go there, I wasn't hoping to find the partial skeleton of a juvenile hominin--I had another set of scientific questions within paleoanthropology. My idea was to explore what happened before Hadar [the site at which the famous Lucy fossil was found] in terms of paleoenvironment, paleoanthropology, geology and stratigraphy. I went with a small group of Ethiopians in 1999 and we found lots of fauna--elephants, pigs, rhinos and what have you. And in 2000 I led a small group of Ethiopians there again. On the 10th of December I decided that we would survey this hillside. That afternoon the second person who was with me--another Ethiopian who was the antiquities officer (Tilahun Gebreselassie)--saw the hominin fossil first, sticking out of the sandstone. I was only a few meters away. Right away it was clear that it was a hominin, with the absence of the brow ridges, the lack of a postorbital sulcus, the small canine, the mandible's vertical symphysis--all those features. So I started looking around [at the surrounding ground] and right away I found part of the forehead. But with only four of us in the group, it was not possible right then to do the necessary excavation. We didn't even have screening materials. I had to go all the way back to Adis Ababa to pick up supplies first.
Of course there was another reason also to go back to Adis. I wanted to make sure this incredible discovery was safe. So I took it to Adis, put it in the safe and then went back to the site, where we recovered some more of the skull. We didn't do much. My goal was to make sure what was exposed was collected. With just a small number of people it's not a good idea to do a huge excavation because it gets out of control. So the idea was to make sure that everything that was eroded out of the sand and everything that was broken off the block of bones and sandstone was collected.
KW: Why has it taken so long to publish your findings?
ZA: When we found the fossil, the face was only partly exposed, and most of the other parts of the body--including the collar bones, the scapulae, at least 10 vertebrae and the ribs were covered by this hard and very compact sandstone matrix. Cleaning that took over five years. And [the work] is not finished yet. We also went back for four successive field seasons, spending two months every year on that spot--with more people--to recover more of the skeleton. The result is what is now the earliest and most complete juvenile Australopithecus afarensis ever found.
KW: How much of the skeleton do you have?
AZ: I would say it is more complete than Lucy. But in addition we have the face, which is not preserved in Lucy. So you can look at her and she looks at you also. We also have the lower jaw--which is still in connection with the upper jaw--and a full brain endocast, which is made of the sandstone impression. Part of the parietal, which is the upper part of the calotte, is gone, so you can see the endocast there. Squashed to the base of the skull are all the bones that I described earlier. So the upper part of body is there, except the arms, but we have a piece of the humerus.?