Capuchin monkeys’ stone-tool use has evolved over 3,000 years

Excavations in Brazil have pounded out new insights into the handiness of ancient monkeys.

South American capuchin monkeys have not only hammered and dug with carefully chosen stones for the last 3,000 years, but also have selected pounding tools of varying sizes and weights along the way.

Capuchin stone implements recovered at a site in northeastern Brazil display signs of shifts during the last three millennia between a focus on dealing with either relatively small, soft foods or larger, hard-shelled edibles, researchers report. These discoveries, described online June 24 in Nature Ecology & Evolution, are the first evidence of changing patterns of stone-tool use in a nonhuman primate.

“It’s likely that local vegetation changes after 3,000 years ago led to changes in capuchin stone tools,” says archaeologist Tomos Proffitt of University College London. The new findings raise the possibility that chimpanzees and macaque monkeys, which also use stones to pound and dig, have shifted their tool-use styles over the long haul, perhaps in response to climate and habitat changes, Proffitt says.

Archaeological sites linked to apes and monkeys are rare, though. Previous excavations in West Africa unearthed nut-cracking stones wielded by chimps around 4,300 years ago (SN: 11/21/09, p. 24). Present-day chimps inhabiting the same part of Africa crack nuts with similar-looking rocks.

Evidence of long-term changes in tools used by wild capuchins (Sapajus libidinosus) comes from a site in Brazil’s Serra da Capivara National Park. Excavations there have also yielded ancient human stone tools (SN: 10/18/14, p. 14). But the newly unearthed artifacts more closely resemble stone tools used by modern capuchins at the same site (SN: 11/26/16, p. 16), rather than Stone Age human implements, the researchers say.

Primatologist Tiago Falótico of the University of São Paulo, Proffitt and their colleagues recovered 122 capuchin stone artifacts from four sediment layers. Radiocarbon dating of charred wood bits in each layer provided age estimates for the finds. Excavated tools consisted of partial and complete pounding stones, rocks used as platforms on which to pound objects, and pieces of rock that detached from pounding stones and platforms during use.

Relatively small, heavily damaged pounding implements from between around 3,000 and 2,500 years ago were likely used to smash open tiny foods such as seeds or fruits with soft rinds, the researchers say. Similar tools uncovered at the site date to around 600 years ago. Larger pounding stones from overlying sediment appeared about 300 years ago. The appearance of bigger capuchin tools by around that time denoted a shift to eating hard-shelled fruits and nuts that required high-impact pounding to open, the team says.

Then starting roughly 100 years ago, capuchins downsized pounding stones slightly to crack cashews efficiently, the researchers suspect. Capuchins living near the site today like to eat cashews that the animals crack with similar pounding stones.

Either of two scenarios accounted for the variety of stone artifacts found at the Brazilian monkey site, Proffitt says. Different capuchin populations may have visited the location at various times, each using particular types of stones to crack or open preferred seeds, nuts or fruits. Or, a single capuchin population may have regularly returned to the site and changed its tool use over time in order to exploit different types of foods.

Stone tool modifications that occurred over the last 3,000 years among Brazilian capuchins are comparable to those observed among West African chimp communities today, says University of Oxford primatologist and archaeologist Susana Carvalho. These chimps use large, heavy stones to crack hard Panda nuts as well as small stones to break open softer palm oil nuts. “What’s novel is that a stone tool pattern we had already seen in chimps today is now recognizable from the archaeological evidence for capuchins.”

Still, differences between large and small capuchin and chimp tools are modest relative to contrasts among ancient hominid tools, such as simple chopping implements and oval hand axes, Carvalho says. Hominids began making and using stone tools at least 2.6 million years ago.