Amphibians are cold-blooded vertebrates, like reptiles, but require a moist environment to survive. Amphibian fossils were first discovered 419 million years ago during the Devonian period. Amphibians are distinguished by their permeable skin, which they use for breathing, absorbing water, and protection through the generation of poison in their skin glands. Amphibians lay eggs, which then go through the process of metamorphosis: the eggs hatch into limbless larvae, which are water hosted creatures that swim, that then transform into limbed adults that live primarily on land and breathe air. An important ecological indicator, due to their especially restrictive habitat requirements, amphibians are the first to die off when their environment is disturbed; this is why over half of all frog species are facing extinction.
The difference between amphibians and reptiles is that reptiles are born with a set of lungs while amphibians are born with gills that help them breathe underwater and then grow lungs and legs later on. Also, reptiles have scales while in comparison amphibians have thin and smooth skin.
Generally, amphibians breathe through their lungs as well as their skin. The skin of amphibians has to stay wet so amphibians can absorb the oxygen to effectively secrete mucous to keep their skin moist. If the skin of amphibians gets too dry, they cannot breathe and will die.
The most common habitats for amphibians are meadows, springs, streams, rivers, lakes, ponds, bogs, and marshes. Amphibians can also be found in swamps, vernal ponds, and farmland. Amphibians have adapted to be able to live almost anywhere and exhibit it through characteristics in their body and behaviors.