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This 1.4 million-year-old hand axe was chipped off a hippo femur

EnlargeBy Diego Delso, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=74486418

Hand axes are fairly common finds at sites dating between 2 million and 1 million years old. These sturdy tools have two sides (also called faces) and a sharp edge at one end. But hand axes are usually made of stone, so archaeologists working at the Konso Formation in southern Ethiopia were surprised to find a hand axe worked from a large chunk of bone buried in a 1.4 million-year-old layer of sediment. When Tohoku University archaeologist Katsuhiro Sano and his colleagues compared the bone to a collection of bone samples from large mammals, they found that their ancient hand axe had once been part of a hippopotamus femur (thigh bone).

From hippopotamus to hand axe

The Konso find is only the second bone hand axe archaeologists have ever found, and one of just a handful of bone tools from sites older than 1 million years. Based on fossils found at Konso, the hominin who flaked off a chunk of hippo femur and worked it into a nice, sharp hand axe was probably a Homo erectus. Members of the species walked upright and were built a lot like modern humans, and they eventually spread from Africa, across Europe and Asia, and all the way to modern Indonesia.

At least one member of this species left behind a 13cm-long hand axe that is, according to Sano and his colleagues, an excellent piece of craftsmanship. The toolmaker apparently flaked a large, flattish piece of bone off the side of a hippo femur; you can still see the outer surface of the bone on one side of the hand axe. That fits the standard Acheulean approach to making hand axes and other tools; the first step is to make a large “blank” in the right general shape, then gradually flake off smaller pieces to shape the finished product.

Its a relatively advanced technique to begin with, compared to some earlier stone toolmaking styles, because it requires planning and also really good control over what breaks (and how it happens) when you hit one piece of stone with another, so that you knock off a flake in the size and shape you want. That kind of control is even harder to accomplish with bone than with stone, and its also harder to find bone big enough to make the right size blanks. Its not for nothing that the only other Acheulean bone hand axe ever found—a 1.3 million to 1.6 million-year-old tool from Olduvai Gorge in Tanzania—was shaped from a piece of elephant bone.

  • Both sides of the 1.4 million-year-old bone hand axe Berhane Asfaw
  • The bone hand axe (micro-ct based render) shown placed in a hippopotamus femur. Gen Suwa

No bones about it—early hominins were pretty sharp

“Finely-shaped bone tools like bone hand axes are extremely rare,” wrote Sano and his colleagues. But the toolmakers at Konso knew what they were about.

The hominin who made the hippo bone hand axe chipped the large bone “blank” into the right general shape, then chipped a series of tiny flakes off one end to make a sharp edge. By alternating those flakes between one face and the other, the toolmaker made a remarkably straight 5cm-long cutting edge at the working end of the hand axe.

“This bone handaxe shows that at Konso, […] H. erectus individuals were sufficiently skilled to make and use a durable cutting edge,” wrote Sano and his colleagues. That lines up pretty well with other evidence that H. habilis and H. erectus understood material properties like sharpness and durability well enough to choose the right material for the right job. Our early hominin cousins were already very resourceful, very competent, and very intelligent.

In fact, that earlier study about material properties raises the question of why this particular hominin chose to make a hand axe out of hippo bone, of all things. There would have been plenty of stone available in the area. Actually, Sano and his colleagues suggest that the abundance of workable stone around Konso may have helped Acheulean toolmakers there hone their craft, since they had plenty of material to work with.

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