Scientists find a hundred new types of frog lurking in the forests of Sri Lanka

Scientists have identified more than 100 new species of frogs inhabiting a small and threatened patch of tropical rainforest in a discovery that underscores our ignorance of the natural world's diversity.

The new species are all tree frogs living in the rainforests of Sri Lanka and are the latest additions to the estimated 1.7 million species of animals and plants known to science. However, increasingly scientists believe that the actual number of species on Earth is many times this number – possibly 10 million or more.

An international team of biologists led by Christopher Schneider of Boston University describes up to 140 new frog species they found in a survey of Sri Lankan rainforests published today in the journal Science. Dr Schneider said: "We have only just begun the process of describing them and giving them names. The range in size from about an inch to four inches and come in all colours."

In recent years, herpetologists have monitored a dramatic global decline in amphibians – frogs, toads, newts and salamanders – so it has come as a surprise to many of them to discover a place where so many tree frogs have survived unnoticed. The concentration of amphibian diversity puts the island on a par with much bigger islands such as Madagascar and Borneo in terms of biodiversity. "Sri Lanka is well explored and has has been studied by many British naturalists so it has come as a surprise to find so many frogs," Dr Schneider said.

Some of the newly-found frogs lay eggs in the forest leaf litter that develop directly into tiny froglets, bypassing the typical tadpole phase. Dr Schneider said this adaptation may explain why these species have managed to survive in a rainforest that in recent decades had dwindled dramatically. "By skipping the aquatic [stage], they may bypass a life stage when they are more vulnerable," he said.

Rohan Pethiyagoda, a researcher at the Wildlife Heritage Trust in the capital Colombo, began a census of Sri Lanka's disappearing species in 1993. To his surprise he kept finding frogs he could not identify during this treks through the 300 square miles of Sri Lankan forest – which once covered 6,000 square miles. Subsequent morphological and genetic study led the researchers to conclude that between 120 and 140 of the species were new to science.

The scientists also compared their frogs with other specimens collected more than 100 years ago. They found that up to 100 species that had been collected in Sri Lanka more than 100 years ago were not among the current finds, suggesting they may since have gone extinct.

Such research exemplifies the problems facing scientists trying to study and preserve global biodiversity. Stephen Blackmore, the Regius Keeper of the Royal Botanic Garden in Edinburgh, says in a separate article in Science that documenting the world's animals and plants is one of the most important goals following the earth summit in Johannesburg this summer.