In 2004, the Global Amphibian Assessment , an IUCN-led initiative, completed a comprehensive assessment of all 5,743 described species of amphibians, which has been updated most recently in 2008 to contain 6,260 species (Stuart et al. (2004) Science 306: 1783-1786) .
Amphibians are a class of cold-blooded vertebrates that include frogs, toads, salamanders, newts and caecilians. Because they are generally developed from an aquatic larval stage to become terrestrial adults, they are sensitive to a range of ecosystem disturbances, making them excellent indicators of environmental quality. They are widely distributed, absent only from Antarctica, oceanic islands and extremely dry deserts.
Amphibians are among the most threatened of all assessed taxonomic groups with many amphibian species on the brink of extinction. It is estimated that 42% of species are threatened worldwide, since many of the 24.5% Data Deficient species are likely to be threatened. The highest level of threat is in the Caribbean, although Latin American countries have large numbers of threatened species. Habitat loss is the principal threat, affecting nearly 4,000 species. Pollution is next, although introduced species, over exploitation, climate change and the emergence of the infectious fungal disease, Chytridiomycosis also threaten species. Disease appears to be a relatively less significant threat in terms of number of species affected, however it can cause sudden and dramatic population declines that are difficult to recover.