The Earth's most successful primates - humans - are on the brink of killing off nearly a quarter of their 625 cousin species, a report has said.
Great apes such as the Sumatran orang-utan and the Eastern gorilla are at risk of vanishing
Hundreds of species of apes, monkeys and lemurs are at risk of becoming the first primate extinctions in nearly a century, Primates in Peril claims.
The report received input from 50 top specialists from Conservation International and other organisations.
Habitat loss and hunting had bought some species to their knees, it said.
The report listed the 25 most critically endangered primates. It said that without swift action, great apes such as the Sumatran orang-utan and the Eastern gorilla of central Africa could vanish altogether.
"If you took all the remaining individuals from the 25 primate species on this list and gave them a seat in a football stadium, they'd all fit," said Russell Mittermeier, president of Conservation International.
The report urges immediate action to curb the destruction by farmers and loggers of forests in which primates dwell, and end the trade in bushmeat and exotic medicines from animal parts.
"If we do nothing, as many as one-quarter of all today's primates will be dead in 20 years," Dr Mittermeier said.
Of the four global regions inhabited by primates, the worst hit is Madagascar, where loss of habitat to traditional slash-and-burn agriculture has left some lemur species, such as Perrier's sifaka, stranded in tiny areas of forest.
More than half of Madagascar's lemurs are on the verge of extinction.
The golden-headed langur of Vietnam and China's Hainan gibbon are down to a few dozen and the Horton Plains slender loris of Sri Lanka has been spotted only four times since 1937.
But despite declining numbers, no primate species actually went extinct last century.
"Amazingly, we've managed to get through the 20th Century without any primate species going extinct," Dr Mittermeier said. "I'd like to think this is partly because of better conservation efforts."