Only one of the 3 major groups of ancient amphibians evolved into the modern salamanders, frogs, toads, and caecilians. Today amphibians have invaded almost every environment where fresh water is available for some period of time. Some spadefoot toads survive in deserts in underground burrows and only emerge during the occasional monsoon rains that fill temporary ponds. Amphibians have many unique characteristics that distinguish them from other vertebrate classes.
Amphibian skin is glandular and lacks scales, feathers, or hairs.
The skin is also permeable allowing for water and gas exchange. This is only one of the methods of amphibian breathing. As the name amphibian implies, most toads and salamanders, exhibit a two-phase life cycle, an aquatic larval stage and a terrestrial adult stage. The amphibian egg is also a distinctive feature. Frogs and toads are also very ecologically diverse, inhabiting aboral, aquatic and terrestrial niches with great success.