About 1.4 million years ago a hominin in what is today Ethiopia painstakingly modified a hippopotamus bone into a hand axe, demonstrating command of advanced "Acheulean technique” that had only been thought to have developed half a million years later.
Stone tools from prehistoric times are quite common. Bone tools from prehistoric times are known but they are not common, whether because the hominins didn’t make as many or because, being organic, they decayed into dust over time.
In the whole time span of the Konso Formation in southern Ethiopia, which is 1.95 million years ago to 800,000 years ago, this hand-axe shaped from a fragment of hippo femur is the only example of an axe made from bone at that site, Katsuhiro Sano of Japan’s Tohoku University, Gen Suwa of the University of Tokyo and colleagues reported Monday in PNAS.
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Hominins had been making tools from about 3.3 million years ago, starting simply by using a rock as a hammer. Several other animals can do that too. The next stage of tool manufacture is called Oldowan technology, which involved some shaping of the raw stone by chipping off flakes with another stone, which was a whole other story. Other animals don’t do that.
Oldowan technology began about 2.6 million years ago and was supplanted by the next stage, the Acheulean, around 1.75 million to 1.6 million years ago.
The innovation of the more sophisticated Acheulean flaking technology was to shape large “blanks” more precisely by knocking off flakes. Also, a single blank could produce a multitude of tools. While the first known appearance of Acheulian blank usage was in Eastern Africa (Ethiopia, Kenya and Tanzania), it would spread everywhere Homo erectus roamed and remain in use for 1.5 million years.
Naturally there was much overlap: Many sites in Africa and Eurasia show that hominins were making and using both types of tools.
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Acheulean technique has been thought to have been quite conservative, which could indicate a constraint in the development of the manufacturers’ perceptive capacities. Yet there were advances from the earliest Acheulean tools, to the ones made in the middle of that period to the end.
Now the stone tools and hippo bone axe found in the Konso Formation in southern Ethiopia, from 1.4 million years to 1.25 million years in age, were worked bifacially, with a sophistication thought to have appeared only half a million years later.
The technique used to make the bone hand axe produces flakes with two ventral faces, indicating that its maker had a “vision” for the rock blank, and planned it. Moreover, the Konso tools also evince advanced workmanship in thinning the tip, reduced sinuosity of the edges, and better symmetry, the archaeologists say.
The number of flaking “scars” on the hippo femur fragment, their distribution pattern and fractures typical of flaking activity indicate anthropogenic endeavor, knapping the bone into a hand axe-like form – rather than, say, being the outcome of simply hunting the hippo and butchering it. Here a tool had clearly been made and moreover, use-wear analysis indicates that the 13-centimeter-long bone handaxe had been used in longitudinal motions: to cut or saw, the archaeologists say.
This bone hand axe is the oldest known, extensively flaked example from the Early Pleistocene, the archaeologists say. The end result at Konso was tools that exhibited three-dimensional symmetry, a feature otherwise discovered only in much later sites in eastern Africa, dating to 1 million to 800,000 years ago.
There were “a handful” of other modified large bones at Konso but none of the others them were shaped like hand axes; and the other tools found there were all made of stone.
The team does note that the tool assemblage at Konso is highly variable, as is the case in other East African hominin sites. This is also a good place to point out that the Konso hominins, at the time – apparently Homo erectus, but it could have been someone else – usually made tools of stone, but also made at least some tools from bone. It is possible that they made a lot of tools from bone but that most of their bone tools decayed over time, as bone does.
What might the Konso hand axe have been used for? We do not know at this stage, but microscopic analysis revealed areas of polish and striation patterns similar to stone hand axes that have been identified as having been used for butchery, the archaeologists write. Certainly erectus was a hunter. It bears qualifying that there is more research usage marks on stone tools than on the rare bone tools.
What does all of this mean? That our picture of the evolution of stone-tool technology and the abilities of primitive human predecessors is a work in progress, and that ancient hominins had rather better capabilities than we thought 1.4 million years ago.