Critically endangered golden-bellied capuchins (Sapajus xanthosternos) are more widespread than researchers previously thought, and stone tools might be the secret to their success.

Although golden-bellied capuchins are usually found in the humid Atlantic Forest of eastern Brazil, Waldney Martins at the State University of Montes Claros in Brazil found a population of the monkeys outside the forest several years ago. “This stayed in my mind,” he says. So he and his colleagues began studying the species in more detail to fully understand its geographical range.