A rare discovery in Ethiopia suggests that prehistoric human ancestors made axes out of hippopotamus bones some 1.4 million years ago. 

The 13-centimeter-long (5.1 inches) shard of bone was discovered at an archaeological site in Konso, southwestern Ethiopia. Published in the journal Proceedings of the National Academy of Sciences, a team of archaeologists from Japan carried out a dating analysis of the layer of rock it was discovered in and concluded it was made some 1.4 million years ago. 

This was long before our species (Homo sapiens) was on the scene, so it was most likely crafted by a Homo erectus, the longest surviving of all our hominin relatives that roamed the world from above about 2 million years ago until at least 250,000 years ago. 

As many other archaeological finds have shown, H. erectus was no stranger to creating tools and is widely known to have fashioned relatively sophisticated stone axes. Scars and scrapings along the fragment of this ax showed that someone had deliberately tempered its shape in a production style known as the Acheulean, complete with a sharp ax-head with a straight 5-centimeter (<2 inch) long cutting edge. 

So far, this artifact might seem like an impressive, but largely unremarkable discovery. However, the researcher team also discovered it was crafted out of an extremely unusual material: hippopotamus bone. 

The large size of the bone fragment indicates it must have been created from a larger animal. The study author sifted through numerous different large mammals around in the Horn of Africa at this time, such as the African elephant, rhinoceros, giraffe, and hippopotamus. Based on the shape and structure of the bone, they concluded it was originally part of a hippopotamus femur, the long and sturdy bone found in the thigh. 

Other studies have shown prehistoric ax heads made of animal bone, mostly elephant, across Africa and Eurasia, including Tanzania, Israel, Ethiopia, and Italy. However, this is only the second Acheulean ax head made from an animal bone by H. erectus and the first to be made from hippo bone.

It isn’t clear why H. erectus would bother making a tool out of such an obscure material, although the researchers say the uniqueness of the object could indicate it held some symbolic meaning. 

“Due to the scarcity of bone handaxes as well to as the remarkable preference for elephant bones, ritual or symbolic purposes rather than functional purposes have been suggested, especially in Europe,” the study authors write. 

Deeper meaning aside, the hippo bone ax does go to show how intelligent and resourceful our extinct ancestors were. H. erectus is known as a “species of firsts”: first known hominin species to walk fully upright, the first to migrate out of Africa, the first to control fire, and possibly the first to make art. As this new hippo bone discovery further shows, modern humans owe a lot to the creativity and ingenuity shown by this hugely important ancestor.