HADAR

site of paleoanthropological excavations in the lower Awash River valley in Ethiopia. It lies along the northernmost part of Africa's Eastern (Great) Rift Valley, about 185 miles (300 km) northeast of Addis Ababa. The Hadar remains include partial skeletons of Australopithecus afarensis, a key species in human evolution. Major archaeological work began at Hadar in the early 1970s and was led by the American anthropologist Donald Johanson. His efforts resulted in the discovery of the first A. afarensis, a 40-percent complete female skeleton that became popularly known as Lucy. Dated to between four million and three million years ago, the remains provided the first evidence that bipedal locomotion preceded increased brain size in hominids. The pelvis and leg bones indicate upright posture, but the jaw and skull bones reveal a limited cranial capacity similar to that of modern chimpanzees. The site has also yielded the earliest known remains of the genus Homo, dated to 2.3 million years ago, along with the earliest known evidence of tool use. Located at the juncture of the Arabian, Somali, and African tectonic plates, the Eastern Rift Valley has experienced significant geologic upheaval. Over the past several million years, numerous volcanic eruptions laid down layers of volcanic ash at Hadar, effectively covering fossil remains with a succession of strata that was systematically identified and dated by researchers. Seismic activity combined with heavy erosion has gradually exposed the region's fossil record, greatly reducing the amount of excavation required to locate hominid remains. These conditions make Hadar one of the world's richest sources of information on the physiology and habitat of hominid species. The lower valley of the Awash Riveri.e., the Hadar areawas designated a UNESCO World Heritage site in 1980. Scientific studies in the region were virtually halted during the 1980s because of political instability and Ethiopian concerns over the removal of fossil artifacts. By the early 1990s excavations were resumed.