The five-inch-long tool—unearthed at the Konso archaeological site in southern Ethiopia—is one of two known bone axes crafted more than one million years ago. Prehistoric implements made out of bone are exceptionally rare: According to Kiona N. Smith of Ars Technica, researchers have only identified a “handful … from sites older than [one] million years.”
The findings, published this week in the journal Proceedings of the National Academy of Sciences, note that the tool’s maker created the ax’s honed edge by carefully flaking off chunks of bone. Tools previously uncovered at the Konso site provide evidence that Homo erectus was skilled at sculpting instruments out of rock; the new discovery indicates that the ancient hominin’s skillset might have applied to bone, too.
Fashioned from a hippopotamus’ thigh bone, the ax suggests “Homo erectus technology was more sophisticated and versatile than we had thought,” co-lead author Gen Suwa, a paleoanthropologist at the University of Tokyo, tells Science News.
“Homo erectus was the first ancestor of modern humans to have human-like body proportions and the first to appear outside of Africa,” wrote Brian Handwerk for Smithsonian magazine in April. “The species appeared in what is now the nation of Georgia 1.85 million years ago and survived in some Indonesian enclaves until as recently as 117,000 years ago.”
Per Ars Technica, the ax was likely made by cleaving off a piece of the hippo’s femur. This chunk, or blank, as it’s called by archaeologists, was approximately the size of the tool desired. An ancient hominin further shaped the tool with the aid of a stone or bone hammer.
The hand ax’s working edge measures roughly two inches long. It shows microscopic signs of wear consistent with the kinds of sawing and cutting motions used when butchering animals.
A similarly ancient specimen found in Tanzania’s Olduvai Gorge is the only other bone hand ax dated to more than one million years ago. Made out of an elephant bone, the tool dates to between 1.3 and 1.6 million years ago. Per Science News, it displays less intricate craftsmanship than the ax found at Konso.
The researchers speculate that the rarity of bone hand axes may stem from the difficulty of finding bones big enough to be broken into blanks, as well as the added technical challenge of chipping off fragments of bone versus stone. The advanced technique used to make the tool is known as the Acheulean approach and was previously thought to have emerged half a million years after the ax’s creation, reports Ruth Schuster for Haaretz.
For now, the reasons behind Homo erectus’ use of bone over stone remain unclear. As the team writes in the paper, “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.”