Tiny Capuchin monkeys entered their stone age with a blow

For years, scientists at the Smithsonian Tropical Research Institute in Panama had whispered about the distant island where monkeys used stone tools. A botanist had witnessed the phenomenon during a long-standing study – but, more interested in flora than in wildlife at the time, she could not linger to investigate. A return to the site would require new funds, good weather for a 56-kilometer boat ride, and days of swimming, hiking and camping in the middle of rocky shores and dense tropical forests. Brendan Barrett, Behavioral Ecologist at the Max Planck Institute of Ornithology in Germany and Visiting Scholar at STRI

But when Barrett and his L last year, colleagues arrived at Jicaron Island, in Coiba National Park, Panama. They thought it was worth it: tiny white-headed monkeys used stones almost like hammers to crush seafood, nuts and other foods.

"We were stunned," said Barrett, the lead author of a new article on discovery, published on the pre-printed bioRxiv website.

That's what makes this really interesting. We are able to make these comparisons to see why this would evolve.

– Brendan Barrett | Behavioral Ecologist at the Max Planck Institute of Ornithology in Germany

Ideal System

The Capuchins are the first animals of their kind observed using stone tools and alone the fourth group of known non-human primates do it. Sophisticated, social and tolerant to observation, they also provide scientists with an ideal system for studying the causes of a species at stone age and could help researchers understand how and why our ancestors have first picked up stone tools over 2 million years ago.

The white-faced capuchins, or Cebus capucinus, are found throughout the tropical forests of Central America. About the size of domestic cats, with nimble black bodies, long, skillful tails and expressive eyes, they live in matrilineal troops of about 20 animals and practice a variety of complex behaviors. They rub the plants on their bodies, potentially as medicines; defend yourself with sticks against snakes; play games by pbading sticks and stones; and engage in strange "link test" rituals that involve sticking their fingers in the nose and the eyes of others – perhaps the monkey equivalent of a trust falls

A year of observation of Jicaron Island residents with dozens of motion-sensing cameras revealed that at least some of these animals are also skilled at handling stone tools. The monkeys were captured by collecting large, heavy pebbles from water courses and shorelines and carrying them to large flat rocks or logs that could serve as anvils.

Standing on two feet, using their tails to anchor against the ground or a nearby tree, they raised their "hammers" over their heads and crushed them on nuts , crabs, snails and other foods – breaking open shells to reveal a good piece.

Monkeys used their stone tools almost daily and often saved stones for repeated use. In one case, a Capuchin arrived at a site of stone tools on the coast, carrying an almendro brew, or "sea almonds". He dropped them on the floor and then opened them one by one.

Strange Observations

Curiously, only male monkeys used stone tools, although females often stuck close to them. This can not be explained by the smaller size of females, since juvenile males were able to use tools.

Even stranger, the use of tools was only observed in a group of Capuchins occupying stretch of shoreline, although Barrett and his colleagues surveyed the area. together Jicaron and two neighboring islands where are also monkeys. In a few cases, scientists have left "experimental" hammers and anvils in places where no stone tools had been found; the monkeys ignored the artifacts, although some Homo sapiens were observed using them to crack open coconuts.

Which leads Barrett to ask: Why is this seemingly significant behavior not prevalent on the island? What's so special about this unique group of tool users?

"That's what makes this really interesting," he said. "We are able to really make these comparisons by looking at why this would evolve."

The paper has not yet been published in a peer reviewed journal, which means that it has not been officially submitted to the. review of other scientists. But Joan Silk, an ecologist of primate behavior at Arizona State University, said the study was a "careful and enjoyable descriptive badysis of this new observation."

"It's just more good natural history to add to We know how animals use tools in nature," she said. "And find out more about the 39 the use of tools in other animals is very interesting because it helps us to see how the use of human tools is different. "

Humans and our Hominean cousins ​​use stones As hammers and anvils, 3 million years ago, until recently, scientists thought we were the only creatures to do so

But in recent decades, chimpanzees have been observed with the help of a whole "toolbox" – not only hammers but also shovels, such as branches for drilling holes in termite nests and "fishing probes" of straw for extracting tasty insects. wide of Thailand, the long-tailed macaques have become tool-users capable of destabilizing the local shellfish population

In South America, scientists have discovered stones to Capuchin monkey hammers that date back at least 700 years. In fact, the use of tools was previously one of the traits used to distinguish this genus, Sapajus, small capuchins of the genus Cebus – including those of Panama.

It always seemed odd, says Barrett, because the Cebus monkeys of Coiba National Park – an archipelago of more than 100 islands on the Pacific coast of Panama – seemed to be great candidates for the new Tool users

Limited Resources

On the one hand, the resources on the islands are limited, so it is advantageous to find new ways to access food. (Most of the world's best tool users – Thailand macaques, New Caledonia crows – live on the islands, noted Barrett.) Animals do not have natural predators, they can to be able to sit

Like humans, the Capuchins are "dietary generalists". Rather than develop some physiological traits suitable for certain types of foods – like powerful jaws to crush nuts or chunks. molars to chew stubborn plants – "they can solve problems and get all kinds of things that way."

Better yet, Capuchins learn fast, are able to take on new eating habits and social by looking at other members of their species

"They independently developed an enormous addiction to culture," said Barrett. "This really makes them a good comparison for human evolution."

To reinforce this comparison, Barrett and his colleagues plan to expand their investigations on the other islands of Coiba National Park and to badyze whether the monkeys have an energy advantage of the 39, use of tools. They are also looking to find in the fossil record of Jicaron where they can discover evidence of the use of this tool.

Given their intelligence, the discovery that Cebus monkeys use stones like hammers is fascinating. Erin Marie Williams-Hatala, paleoanthropologist at Chatham University in Pittsburgh

But the use of stone tools is considered a "reference" by scientists because that "stone preserves", she said. "Most of what we know about early humans and their behavior is through the stone disk, so there is a huge bias towards it."

She is also interested in the behavior of animals. t be seen in the fossil record – and, indeed, could never have occurred to ancient humans. Orangutans build elaborate nests using engineering know-how that would impress any architect. Some female chimpanzees sharpen sticks with their teeth and use them to impale bush babies for food. More and more chimpanzees use moss or chewed leaves as sponges to absorb hard-to-reach water

"I would die from dehydration before thinking about it," says – she laughing If anything, continued Williams-Hatala, the growing number of species known to use all kinds of tools "shows that under the right circumstances, a wide variety of Animals will find a way to survive. "

But survival, even in an uninhabited and inaccessible place like Coiba National Park, is not always easy for animals on a planet increasingly altered by humans. Barrett noted that investigations by researchers have also uncovered piles of garbage discharged from the ocean. Photographs of Capuchin traps using tools show an environment littered with empty plastic bottles and foam containers.

"Even in these wild and immaculate places where there is so much to discover" to have a rather depressing human footprint. "