However, the surface on which they were found is bracketed by two well-dated deposits of volcanic tuff, the higher one at 3.24 million years and the lower one at 3.42 million years. Unfortunately, the two marked specimens were found on the surface and had very little rock adhering to them, so they could not be linked definitely to any particular stratigraphic layer. His judgments were confirmed by an advanced graduate student and a former student in taphonomy, who made independent assessments of the marks. Two other bones had marks that were too ambiguous to identify. He became convinced that the marks on two of the specimens (a rib and a femur, both probably from antelopes) were unambiguous cut marks, some of which graded into percussion marks made by striking the bone with a hammerstone rather than slicing.
There were no identifiable stone tools or sharp stone fragments found in those areas.īack in the United States, taphonomist Curtis Marean of Arizona State University examined the marks microscopically and compared them with his large collection of bones with known taphonomic histories. Eventually they collected four specimens with intriguing marks on their surfaces for further study. They decided to return to that area and several others to inspect every fragment of fossilized bone for similar marks. Based on field inspection, he thought these might be cut marks made by a stone tool, so he brought the bone back to camp and showed it to the rest of the team. In 2009 paleontologist Denis Geraads of the French Centre National de la Recherche Scientifique was collecting bones from the surface of one area and noticed, on one calcaneum (a foot bone) from an antelope, a set of obvious, unusual marks. The most spectacular has been the partial skeleton of a young Australopithecus afarensis-the same species as the Lucy skeleton-that has been nicknamed “Selam” or “the Dikika baby.” Selam is 3.3 million years old by geological standards and was about 3 years old at death by human standards. The team has been working in the Lower Awash Valley for 11 years and has made impressive finds. Taphonomists strive to reconstruct what has happened to a fossil, from the time it was a living organism until it was found, and to deduce what that history tells us about the ancient environment and adaptive niche of the animal, including how it died. The team includes geologists, experts in radiometric dating, archaeologists and paleontologists, as well as experts in an obscure specialty called taphonomy, which is one of my own areas of expertise.
The Dikika Research Project team is led by Zeresenay Alemseged, curator of anthropology at the California Academy of Science. An international team found themselves in this sort of situation, with new evidence contradicting established theories, when surveying for fossils in the Lower Awash Valley of the Dikika region of Ethiopia-and they opted for publication.
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