An international search has been launched to rediscover 100 species of "lost" amphibians, including the golden toad, Jackson's climbing salamander and the hula painted frog.
The unprecedented global hunt is taking place in 14 countries on five continents and comes as amphibian populations suffer a startling decline in numbers.
Some of the potentially extinct species on the list have not been seen for several decades, including the Turkestanian salamander, which was last seen in 1909.
More than 30% of all amphibian species are threatened with extinction.
Scientists say amphibians are particularly sensitive to the environment and act as an indicator for environmental damage. Amphibians also play the vital role of controlling insects that spread disease and damage crops.
They help maintain healthy freshwater systems and the chemicals in amphibian skins have been used in the creation of life-saving drugs, including a painkiller two-hundred times more potent than morphine.
Launching the campaign, Dr Robin Moore, of Conservation International, said: "Amphibians are particularly sensitive to changes in the environment, so they are often an indicator of damage that is being done to ecosystems.
"But this role as the global 'canary in a coal-mine' means that the rapid and profound change to the global environment that has taken place over the last fifty years or so - in particular climate change and habitat loss - has had a devastating impact on these incredible creatures."
A pathogenic fungus has increased problems for amphibians, causing chytridiomycosis, a disease that has wiped-out entire populations.
People can follow the search for the lost amphibians at www.conservation.org/lostfrogs.