An adult Caquetá titi monkey (Callicebus caquetensis)
A new species of titi monkey has been discovered in a Colombian Amazon expedition. Caquetá titi monkey or Callicebus caquetensis is about the size of a domestic cat with a bushy red beard. Totaling to only about 250 individuals, this newly discovered species is also critically endangered due to severe fragmentation of its habitat.
Along with the news of the discovery is the published paper by Defler et al. (2010), Callicebus caquetensis: A New and Critically Endangered Titi Monkey from Southern Caquetá, Colombia (free pdf). In it, they described the morphology and distribution of the Caquetá titi monkey.
For more about the discovery, read Pictures: Bushy-Bearded Titi Monkey Discovered on National Geographic.