It's a rare thing to witness the extinction of an entire class of animal. We weren't around to see the dinosaurs disappear, and the dodo was just one species of bird -- it's not like all birds slowly disappeared. But according to many conservation scientists, that's exactly what amphibians are facing: Frogs and others in the amphibia class are on their way out unless the conservation community takes immediate action.

The amphibia class in general -- frogs are just the most populous group of the class, which also includes salamanders and caecilians -- has actually been on the decline for some time. Pollution, global warming and habitat destruction from human development have already taken a serious toll. Frogs, in particular, have suffered, having lost an estimated 170 species in the last 10 years alone, with another 1,900 in a threatened state, which is one step below the endangered designation (meaning extinction is imminent). But only part of the destruction is man-made. A fungus identified in the last decade seems to be speeding up the death of the worldwide frog population exponentially. The chytrid fungus coats the frog's skin and makes its pores non-functional. Because a frog relies on its porous skin for hydration and for some of its respiration, the fungus essentially cuts off its water supply and makes it difficult to breathe. In the end, the frog dies from dehydration.

Scientists believe the fungus may have begun spreading around the world in the 1940s, when African clawed frogs -- one of the only species known to be immune to the effects of the fungus -- were shipped around the world for use in medical research, specifically pregnancy testing. African clawed frogs lay eggs when they're injected with the urine of a pregnant human. It's possible that the African fungus then started attacking other frog populations, which had no immunity to it. The discovery of chytrid fungus and its devastating effects on the amphibian population has led to the development of a $500 million project called Amphibian Ark.

Amphibian Ark calls on all zoos, botanical gardens and aquariums around the globe each to take in 500 members of at least one species of the amphibian class. The zoo will clean each animal to make sure the fungus doesn't make it into the protected population, and then isolate the population. The idea is to salvage members of each of the roughly 6,000 remaining species until science has found a way to stop the spread of the fungus in the wild. Once the fungus has been controlled, the zoos will release the frogs, salamanders and caecilians back into the wild. Conservationists see the protective action as an absolutely necessary step in assuring that future generations will know what a frog sounds like, that South America won't be overrun by disease-carrying mosquitoes, and that live-saving medicines will continue to be extracted from frogs. Pain killers rely on frogs for at least one active ingredient, and AIDS researchers have found a chemical in frogs that seems to have an anti-HIV effect.

There are reports that two-thirds of several amphibian species in Central and South America are gone. The mountain yellow-legged frog has nearly disappeared from Yellowstone National Park, and most of the park's remaining members of the species have the fungus. In January 2007, Japan found its first cases of the fungus in its frog population.

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