A monkey that purrs like a cat is among hundreds of new animals and plants found deep in the Amazon rainforest.
Described as "remarkable" by the World Wildlife Fund (WWF), the Caquetta titi monkey, or Callicebus caquentensis, was one of 441 new species discovered between 2010 and 2013.
It was spotted in Colombia by a team including scientist Thomas Defler, who said the animal had an endearing trait.
"When they feel very content they purr towards each other," he said.
The new creature is one of about 20 species of titi monkey, all of which live in the Amazon Basin.
Much of the rainforest - the largest in the world, covering around a third of South America - is yet to be fully explored.
The monkey was the only new mammal to be found during the four-year study of the Amazon, which also revealed 258 plants, 84 fish, 58 amphibians and 18 birds, as well as numerous insects and invertebrates.
A shy lizard with "war paint" markings, a vegetarian piranha that eats river weeds and a thimble-sized frog were among the animals discovered.
Damian Fleming, head of programmes for the Amazon at WWF UK, said: "The richness of the Amazon's forests and freshwater habitats continues to amaze the world.
"The more scientists look, the more they find.
"With an average of two new species identified every week for the past four years, it's clear that the extraordinary Amazon remains one of the most important centres of global biodiversity."
However, the WWF warned the rainforest remains under threat from tourism and deforestation, with the equivalent of three football pitches of land lost every minute.
Initiatives like Sky Rainforest Rescue , which is helping to save one billion trees in the Brazilian state of Acre, are designed to preserve the Amazon's biodiversity for future generations.