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Frog Mystery Solved

Ever since frogs started sprouting extra limbs in ponds and swamps across the country, scientists wondered, was it pollution? The hole in the ozone layer? Now, after years of research, they've cracked the case of the deformed frogs, reports CBS News Correspondent Elizabeth Kaledin.

"We've got the first solid evidence for something that's causing these deformities in nature, so that's very good news," said Stanley Sessions, a biologist at Hartwick College.

Like canaries in a coal mine, frogs have long been considered indicators of the overall health of the environment we live in. The concern was that whatever was harming frogs could potentially harm people too.

But two new studies say the culprit is not pollution but something that's been around for millions of years, a microscopic parasite called a trematode.

The trematode burrows into the hindquarters of tadpoles, scrambling limb cells and often causing extra legs to grow.

Researcher Pieter Johnson of Claremont McKenna College has studied frog deformities specific to northern California for several years.

"A single agent - namely parasite infection - can cause not only extra limbs, but missing limbs, skin webbings and a wide varieties of other limb deformities," Johnson said.

Interior Secretary Bruce Babbitt says the news about parasites may be a relief, but cautions it is too early to dismiss larger environmental problems.

"A species weakened by parasites may be more susceptible to the effects of climate change or to the effects of chemicals, so we still have a big mystery to untangle," Babbitt said.

For instance, what's causing other types of frog deformities and why are entire populations of frogs disappearing? Still, scientists say the discovery is a small leap forward.

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