An expedition to the remote Urubamba River in Amazonian Peru has led explorers to discover a new species of monkey named the Urubamba brown titi or Callicebus urubambensis. With this discovery, there are now a total of 34 known species of titi, reaffirming its claim as the largest group of South American monkeys. The new monkey is just the size of a domestic cat and roams with others of its kind, making it a social animal.

Co-discoverer Jan Vermeer, coordinator of the Peru-based primate research programme, Proyecto Mono Tocón, told New Scientist: "Its appearance is very distinct from other titis, the entire body and tail are much darker, and the face is all black." The distinctive colour patterns that each titi species develop is thought to be closely linked to its evolution.

What has come as a surprise to scientists is that it appears to be a new monkey species that is not endangered. Vermeer said: "So often when a new monkey is discovered it is already threatened with extinction. This is a remote area with very little hunting, so for once this is not the case." The Urubamba brown titi is rather common across a 350km stretch across the forest.

Stephen Ferrari of the Sergipe Federal University in Brazil, also told New Scientist that there is still a lot to be learned about titi monkeys as a collective species. "Titi monkeys are small and discreet. We are only just beginning to understand the factors driving their diversity," he said. "A few decades ago, only five titi species were known. I think many more will be discovered as we explore southern Amazonia's biologically uncharted forests."