A team of scientists have discovered three species of amphibian previously thought to be extinct. Their finds include a cave-dwelling salamander last seen in 1941 – the same year that it was discovered – and two species of frog that dwell in west Africa. In total, the scientists hope to rediscover roughly 100 species of amphibian.

Conservation International, in conjunction with the IUCN Amphibian Specialist Group, has organised a string of international expeditions to search for "lost" amphibian species that are highly threatened by habitat loss, climate change and disease. More than one third of amphibian species are under threat of extinction.

One of the creatures discovered by the team is the cave splayfoot salamander, Chiropterotriton mosaueri. After abseiling into a humid cave fringed with pine and oak forest in Mexico, the team found the salamander clinging to a crevice. It was last seen 70 years ago.

On a separate expedition to the Ivory Coast, scientists spotted a red-limbed Mount Nimba reed frog in a swamp near the Liberian border. The frog, which was last seen in 1967, is in urgent need of protection as the forests of Mount Nimba are threatened by deforestation, according to Conservation International.

In the flooded forests that sit on the banks of the Congo river, the team also discovered an Omaniundu reed frog, Hyperolius sankuruensis. Speckled with bright green spots, the frog was last seen in 1979. Because it only emits short, infrequent calls late at night, it is extremely hard to find.

"Indeed, because so many species of amphibian are tiny and live under rocks in streams or in other hard to find places, it is very impressive that these expeditions have found just three species previously thought to be extinct," says David Sewell, who studies amphibian conservation at the School of Anthropology and Conservation at the University of Kent.

But despite the finds of species thought to be extinct, there's no reason to rejoice yet, says Sewell. "Finding three species is brilliant, but what about the remaining 97 species that the expeditions set out to find? While we live in hope that these species will be rediscovered, most of them are probably extinct."

Among the 97 species that have not been espied by the team are the sharp-snouted day frog, Schneider's banana frog and the gastric brooding frog, which lives underneath rocks in streams in Australia. Females swallow their eggs and raise tadpoles in their stomach. During that time, their stomachs stop producing hydrochloric acid.

Rediscovery of this frog would have interesting implications for medicine, says Sewell. For example, understanding how the frog downregulates production of hydrochloric acid could lead to novel ways to treat stomach ulcers. But rediscovery is unlikely, given that the frog was last seen in 1985 and is listed as extinct on the IUCN Red List, he says.

Trevor Beebee, a conservation geneticist based at the University of Sussex, is more optimistic. "Proving extinction is a notoriously difficult thing to do, especially in remote and complex habitats such as rainforests. Another hard look at amphibian extinctions might therefore generate at least a little much-needed optimism."