one of the most productive hominid fossil-bearing sites in Africa. Roughly 300 km (186 mi.) northeast of Addis Ababa and situated in the west-central Afar Depression of Ethiopia (11°10′ N, 40°35′ E), the mid-Pliocene site of Hadar takes its name from a large wadi known by the local Afar tribesmen as the Kada Hadar. Paleontological field investigations at Hadar during 1973–1977, 1980, 1990, and 1992–1994 have produced more than 300 hominid fossil specimens. Most noteworthy is nearly 40 percent of a single skeleton (nicknamed Lucy) and the partial remains of at least thirteen individuals (the so-called First Family) from a single geological stratum at.
The fossiliferous deposits, extending over roughly 100 sq km (39 sq. mi.) and known as the Hadar Formation, consist of 160 to 270 m (525–886 ft.) of lacustrine, lake-margin, and fluvial sediments. Widespread and distinctive volcanicmarker beds permit the subdivision of the formation into four stratigraphic members (from bottom to top): Basal, Sidi Hakoma, Denen Dora, and Kada Hadar.
In 1968 Maurice Taieb first visited Hadar and recognized its great potential for paleoanthropological research. Following a regional survey of sites in the Afar Depression In 1972, Taieb established the International Afar Research Expedition with his coworkers Donald C. Johanson, Yves Coppens, and John E. Kalb. Based on geological considerations as well as the superb preservation of faunal remains, the team initiated intensive study of Hadar In 1973. It was then that the first fossil hominid, a knee joint, confirmed the presence of human ancestors within the Hadar Formation.
The sparsely vegetated and heavily eroded outcrops at Hadar permitted the recovery of close to seven thousand fossil specimens of a wide variety of carnivora, poboscidea, perissodactyla, artiodactlya, rodents, birds, reptiles, fish, nonhominid primates, and other mammalian taxa. The faunal picture is characteristically African (Ethiopian faunal region) and indicates a mosaic of habitats, ranging from closed and open woodland bush and grassland conditions. Fossil pollen and microfauna indicate that the elevation of site was considerably higher than the present day altitude of 500 m (1,640 ft.).
Age calibration of the Hadar Formation is now firmly established on the basis of vertebrate biostratigraphy (correlation to other sites of known absolute age), paleomagnetism, and fission track dating as well as K-Ar and 40Ar/39Ar dating of the volcanic horizons. The hominid fossil-bearing strata at Hadar span a time range from at least 3.4 million years to approximately 3.0 million years ago. The best age estimate for the Lucy skeleton is 3.2 million years old.
Detailed anatomical study of the Hadar hominid collection led to the recognition that they were morphologically identical with those from the 3.5-million-year-old site in northern Tanzania known as Laetoli. In 1978, because of the recognition of a number of primitive cranial, mandibular, and dental characteristics these hominid fossils were distinguished from other known hominids, and placed in a new species, Australopithecus afarensis (Johanson et al., 1978). Although individual anatomical features are seen in other species of Australopithecus it is the constellation of features in A. afarensis that makes this species distinct.
A. afarensis is sexually quite dimorphic, and males are considerably larger than females. The locomotor skeleton, represented in the Hadar collection including the lower limb, the pelvis, and the foot, as well as the remarkably well preserved hominid footprints from Laetoli indicate that A. afarensis was fully bipedal. Some investigators have pointed out that primitive features in the pelvis, ankle, and foot suggest a more arboreal lifestyle for this species. However, it is more likely that these features are merely “evolutionary baggage” from an arboreal ancestry.
Now widely recognized as a distinct hominid species, Australopithecus afarensis with its amalgam of primitive and advanced features is currently the best link between an ancient ape ancestor and more recent hominids. Although the precise geometry of the human family tree is widely debated, this primitive species of Australopithecus is considered to be an ancestor to all later hominids, including the lineage which ultimately led to modern Homo sapiens.
No archaeological traces have been found in association with the Hadar fossil hominids. However, during survey and limited excavation in the Gona area, west of the hominid bearing deposits at Hadar, lithic artifacts were found. The flakes and cores are broadly assigned to the Oldowan industry. They are stratigraphically above the hominid bearing deposits and have been estimated to be approximately 2.5 million years old, making them among the oldest stone tools in Africa.
- Aronson, James L., and Maurice Taieb. “Geology and Paleogeography of the Hadar Hominid Site, Ethiopia.” In Hominid Sites: Their Geologic Settings, edited by George Rapp and Carl Vondra, pp. 165–195. Washington, D.C., 1981.
- Johanson, Donald C., et al. “A New Species of the Genus Australopithecus (Primates: Hominidae) from the Pliocene of Eastern Africa.” Kirtlandia 28 (1978): 1–14.
- Johanson, Donald C., and T. D. White. “A Systematic Assessment of Early African Hominids.” Science 203 (1979): 321–330.
- Johanson, Donald C., and Maitland A. Edey. Lucy: The Beginnings of Humankind. New York, 1981.
- Walter, Robert C. “Age of Lucy and the First Family: Single-Crystal 40Ar/39Ar Dating of the Denen Dora and Lower Kada Hadar Members of the Hadar Formation, Ethiopia.” Geology 22 (1994): 6–10.
Donald C. Johanson