By Alex Kirby
BBC News website environment correspondent
A species of monkey unknown to science has been photographed in India by an international team of researchers.
The Arunachal macaque: A surprise to science
The monkey, a member of the macaque family, was sighted in the state of Arunachal Pradesh, which lies in the country's remote north-eastern region.
Named the Arunachal macaque, the new monkey is a comparatively large brown primate with a relatively short tail.
The scientists say they are surprised to have found a hitherto unknown large mammal in such a populous country.
Wildlife treasure trove
The discovery was made during expeditions last year and this by Indian researchers from the New York-based Wildlife Conservation Society, the Nature Conservation Foundation, the International Snow Leopard Trust, and the National Institute of Advanced Studies.
The last species of macaque to be discovered in the wild, the Indonesian Pagai macaque, was described in 1903.
The Arunachal macaque (Macaca munzala) is described in a forthcoming issue of the International Journal of Primatology.
Recent expeditions into Arunachal Pradesh by WCS's Indian partners have also reported the leaf deer, the black barking deer, and the Chinese goral (an animal related to the goat), all species that were previously unknown from India.
After one such expedition, the state government created a new protected area - the Tsangyang Gyatso Biosphere Reserve.
Dr M D Madhusudan of WCS said: "This new species comes from a biologically rich area that is perhaps India's last unknown frontier. The discovery of a new species of monkey is quite rare.
"What is also remarkable about our discovery is that few would have thought that with over a billion people and retreating wild lands, a new large mammal species would ever be found in India, of all places.
"This region of Arunachal Pradesh, with its rugged mountains and extensive forest cover, is truly one of India's last wild places, one that merits protection at both regional and international levels."
WCS says: "Although the monkey is new to science, the animal is well known to the residents of the Himalayan districts of Tawang and West Kameng, where the species occurs.
"The monkey's species name, mun zala, means 'deep-forest monkey' in the vernacular of the Dirang Monpa people."
The new species is one of the highest-dwelling primates in the world, occurring between 1,600 and 3,500m (5,250-11,500ft) above sea level.
It is not hunted for food or sport, but local people do kill monkeys in retaliation for crop-raiding. The team does not yet know whether the Arunachal macaque is endangered.