Amphibians

What are they?

Amphibians include any member of a class of cold-blooded vertebrate animals that lie inbetween the evolutionary development of fishes and reptiles. Included among them are more than 4 living species which are the frogs and toads, salamanders and newts, and caecilians .Amphibians were the first vertebrates to move from an aquatic habitat to a terrestrial one, and they are the ancestors of all reptiles, birds, and mammals.

Amphibians are species of the class Amphibia and are vertebrates easily distinguished by their remarkable ability to take advantage of both aquatic and land habitats. The name amphibian, suits its nature - being derived from the Greek amphibios meaning "a double life," . Despite this distinction, however, some species are confined to the land , while other species have a completely aquatic existence

Habitat

Although a few species live their lives in water, most live at a portion of their's on land. They are distributed worldwide, but the majority are found in the tropical regions of the earth. Most amphibians have an aquatic larval, or tadpol, stage that metamorphises into an adult.

Evolution of amphibians

Amphibians are believed to have evolved from either the lobe-fin fishes (Crossopterygii) or the lungfishes (Dipnoi) of the Early Devonian Period ( lasting from 408 to 387 million years ago). These fishes had an advantage over other fishes by the fact that they had lungs. They could breathe on land too! In time of shortage of water, these fishes probably came out of the pools which were drying out on their muscular fins to search for other water. They might have added insects and other small arthropods to their diet while moving and over time became less dependent on water. A caecilian fossil from the Paleocene Epoch (66.4 to 57.8 million years ago) has been found in Brazil.

Salamanders apparently evolved in the Northern Hemisphere, but the earliest frogs, dating from the Jurassic Period, evolved south of the Equator.