Berkeley — Scouring the dry washes encircling an Ethiopian site where scientists seven years ago found fossils of 4.4 million-year-old human ancestors, University of California, Berkeley, graduate student Yohannes Haile-Selassie has found even older fossils that show human ancestors walked on two legs as early as 5.2 million years ago. The fossils are the earliest hominid known, and date from close to the time when human ancestors are believed to have split off from the chimpanzees on the first steps of their evolutionary trip to modern Homo sapiens. The fragmentary fossils, which include teeth, a jawbone, hand, arm and collar bones, and one toe bone, appear to be from family members of the species discovered in 1994 by an international team led by UC Berkeley paleoanthropologist Tim White. They named that species Ardipithicus ramidus, and concluded that it was the earliest known human ancestor. Haile-Selassie, for now, has designated the new fossils as a subspecies of this earlier find: Ardipithicus ramidus kadabba. "Its dentition is that of a hominid, its toe bone is like that of a bipedal animal," said Haile-Selassie from Addis Ababa, where he continues to study the fossils at the National Museum of Ethiopia. "It's definitely a hominid, and proves that the earlier 4.4 million-year-old Ardipithecus ramidus was a hominid, not an ape." Haile-Selassie reported his finds in the July 12 issue of Nature. A second paper in Nature by geologist Giday WoldeGabriel of Los Alamos National Laboratory, coauthored by Haile-Selassie, White and others, described the paleoclimate of the area Ardipithecus roamed nearly 6 million years ago. The publication of these two papers by Haile-Selassie and WoldeGabriel, both Ethiopians, is a major milestone in African paleoanthropology, according to White, a professor of integrative biology. "These two local scholars have joined the international scientific community at the highest level," said White, a faculty member in the College of Letters & Science. "This is a huge development in African paleoanthropology and a welcome change in the conduct of this science. | |
Hominid fossils belonging to Ardipithecus ramidus kadabba, found in 1997-1999. The mandible of the subspecies is at upper left, the toebone is in the right upper row, and the hand holds a fragment of collar bone. |
"UC Berkeley has played a major role in this. Beginning with J. Desmond Clark and Clark Howell, we have had a program for many years at Berkeley of nurturing and training people from developing countries to do paleoanthropology. This is an example of how that has paid off scientifically, for Africa and for Ethiopia."
Clark and Howell are professors emeriti of anthropology at UC Berkeley and among the most respected anthropologists working in Africa during the past century.
Haile-Selassie found the new fossils along the western margin of the Afar rift in the Middle Awash region of Ethiopia, about 140 miles northeast of the capital Addis Ababa and 25 kilometers from the Aramis site where White's team found A. ramidus. The fossils came from sites in four different arroyos draining the margin and one closer to the Aramis discoveries. These sites were identified by first surveying the area with satellite imagery and air photos, then on foot, and finally, after the areas were determined to be possible fossil sites, with an intensive survey to establish their age based on fossils evidence.
"When you don't find anything, an hour is like a day," Haile-Selassie said about discovering the first fossil — a mandible or jawbone with one molar — in 1997. "But when you find good stuff, you don�t even want night to come, you want to work 24 hours to find more. That's how exciting it was."
Discovery in 1998 by Yohannes Haile-Selassie of an Ardipithecus ramidus kadabba canine tooth. This tooth, recovered while sieving loose sediment at the site, is different from the canine teeth of all modern and extinct apes. Instead, it resembles later hominids. Based on his analysis of this tooth and other fossils, Haile-Selassie has interpreted these fossils to represent our earliest ancestor this side of the common ancestor we once shared with modern chimpanzees. The tooth and other fossils are dated to 5.7 million years ago.