The development that took place in the Lower Valley of the Awash changed the history of mankind. The hominid remains excavated there are characteristic of a unique type.

Most of the Miocene and Plio-Pleistocene palaeo-anthropological localities that have provided information about the ancestors of mankind are concentrated in the East African Rift System. This is due to the fact that volcanic and tectonic activities were responsible for creating dynamic environments for the proliferation of life and the preservation of faunal and floral remains within the confines of the rift. Volcanic and tectonic activities related to rift evolution created plateaus and mountains; most of the sediments in the basins were derived from these topographic highs located within and outside the rift valleys. Lavas, volcaniclastic sediments, and tephra were responsible for the quick burial and preservation of fossils.

However, there are numerous gaps in the fossil record representing an important period (10-5 million years BP) pertinent to the understanding of the pongid/hominid split and the extinction and appearance of numerous taxa. The Middle Awash valley contains late Miocene fossiliferous sedimentary sequences that can fill this gap. Detailed geological, palaeontological, palaeoenvironmental, and palaeoecological studies in the Middle Awash fluvial and lacustrine fossiliferous sedimentary rocks are addressing the environment-related evolutionary issues.

From 1973 to 1976, a team of international specialists working in the Lower Valley of the Awash excavated a large entire of extremely well-preserved human and animal fossils. These remains, the oldest of which are at least 4 million years old, constitute evidence of human evolution which has modified the history of mankind. The most complete fossil found at this site is the remains of the skeleton of a humanoid, certain traits of which link it with the australopithecine species whereas certain others place it with Homo sapiens. The most spectacular discovery came in 1974 at the site of Hadar, when 52 fragments of a skeleton enabled the famous hominid known as Lucy to be reconstructed.

The term ‘hominid’ refers to a member of the zoological family Hominidae; hominids share a suite of characteristics which define them as a group. The most conspicuous of these traits is bipedal locomotion, or walking upright. As in a modern human’s skeleton, Lucy’s bones are full of evidence clearly pointing to bipedality. At Hadar the size difference between males and female is very clear, with larger males and smaller females being fairly easy to distinguish: Lucy clearly fits into the smaller group.

The hominid-bearing sediments in the Hadar formation are divided into three members. Lucy was found in the highest of these, the Kada Hadar member. Although fossils cannot be dated directly, the deposits in which they are found sometimes contain volcanic flows and ashes, which can be dated. According to these dates Lucy is dated to just less than 3.18 million BP.

Although several hundred fragments of hominid bone were found at the Lucy site, there was no duplication of bones. The bones all come from an individual of a single species, a single size, and a single developmental age. In life, she would have stood about 1 m tall and weighed 27-30 kg. There are several indicators which give an idea of her age: her third molars; all the ends of her bones and her cranial sutures indicate a completed skeletal development; her vertebrae show signs of degenerative disease. All these indicators, when taken together, suggest that she was a young, but fully mature, adult when she died. No cause has been determined for Lucy’s death. The remains are stored in a specially constructed safe in the Paleoanthropology Laboratories of the National Museum of Ethiopia in Addis Ababa.

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