From Scientific American:
The monkey is a wild capuchin in northeastern Brazil’s Serra da Capivara National Park, where these animals have long been known to use rocks for a wide range of activities, from cracking open nuts and digging for roots to catching the attention of potential mates. Other nonhuman primates, including West African chimpanzees, also use rocks as tools in the wild. But the Serra da Capivara capuchins are the only ones that scientists have seen banging rocks together to break them—an activity previously thought to be exclusive to members of the human family. Humans do it to create sharp-edged tools for cutting things. The capuchins, in contrast, have never been seen using the flakes they make; they just lick the surface of the embedded stone, perhaps in pursuit of mineral dust.
Now a new study has examined the capuchin-produced stone flakes, and it turns out that the chips meet criteria used to distinguish human tools from naturally broken rocks. The findings, published in fall 2016 in Nature, could fuel debate over controversial archaeological sites. The discovery also raises questions about what differentiates humans from other primates and how our lineage started fashioning implements from stone.
Tomos Proffitt of the University of Oxford and a group of his colleagues watched the capuchins select rocks to use as hammers and subsequently strike them against cobbles. The researchers retrieved the fragmented stones and also collected other such artifacts found in excavations within the surrounding area—just as they would if they were excavating a human archaeological site. They then analyzed this collection of 111 capuchin artifacts, examining their shapes and sizes, as well as the nature of the scars left on the rocks by all the bashing.
Remarkably, the team found that the capuchin artifacts exhibit distinctive scoop-shaped, or “conchoidal,” flaking and sharp edges and that the monkeys …