Amphibians

Amphibians are a class of cold-blooded (in the traditional sense) animals that include the frogs, toads, newts, salamanders and caecilians. These familiar animals evolved during the Devonian period, around 370 million years ago, from lobe-limbed fish similar to today's coelacanths and lungfish. While superficially similar to some lizards, amphibians require a body of water in order to complete their breeding cycle. They also have semi-permeable skin, through which they can breathe and this feature, among others, make them susceptible to environmental pollution and, as such, they're often regarded as an indicator species. Today, the class comprises some 8,000 species worldwide, the majority (almost 90%) of which are frogs.