A lucky encounter with a hunter who had just bagged one of these mystery monkeys allowed the scientists to confirm their hunch: they had, indeed, found a new species.
C. urubambensis is probably not endangered, though the IUCN has not had time to make an assessment.
The likely range of their habitat is large and sparsely populated, and has not been decimated by deforestation.
Also, titis are not prized by local hunters, who favor larger prey such as spider, woolly and howler monkeys, Vermeer explained.
"If you pay 25 cents for a bullet, you prefer to shoot an animal weighing 10 kilos, not one," Vermeer said.
While a huge success, the expedition did not come without a cost: one member of the team fell sick with malaria, and another checked into a hospital with acute abdominal pains.
At one point, members of an indigenous community -- bows drawn -- threatened to skewer the intrepid biologists with arrows.
That is when Vermeer remembered an air strip they had seen cut from the jungle, probably to transport cocaine, his guides said. "It wasn't for Doctors Without Borders," Vermeer quipped.