The 3 Basic Amphibian Groups

A Beginner's Guide to Amphibian Classification

Water Frog

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Amphibians are a group of tetrapod vertebrates that include modern-day frogs and toads, caecilians, and newts and salamanders. The first amphibians evolved from lobe-finned fishes approximately 370 million years ago during the Devonian Period and were the first vertebrates to make the move from life in water to life on land. Despite their early colonization of terrestrial habitats, most amphibians never fully severed their ties with aquatic habitats. Along with birds, fish, invertebrates, mammals, and reptiles, amphibians are one of the six basic animal groups.

About Amphibians

A tree frog

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Amphibians are unique in their ability to live both on land and in water. There are about 6,200 species of amphibians on Earth today. Amphibians have certain characteristics that separate them from reptiles and other animals:

  • They are born in water and then metamorphose (change) into adults that can live on land.
  • Amphibians can breathe and absorb water through their thin skin.
  • They have many different ways of reproducing: some lay eggs, some bear live young, some carry their eggs, while still others leave their young to fend for themselves.

Newts and Salamanders

Smooth Newt

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Newts and salamanders are slender-bodied amphibians with long tails and four legs that diverged from other amphibians during the Permian Period (286 to 248 million years ago). Newts spend most of their lives on land and return to water to breed. Salamanders, in contrast, spend their entire lives in water. Newts and salamanders are classified into about 10 families, some of which include mole salamanders, giant salamanders, Asiatic salamanders, lungless salamanders, sirens, and mudpuppies.

Frogs and Toads

Red-eyed tree frog

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Frogs and toads belong to the largest of the three groups of amphibians. There are more than 4,000 species of frogs and toads, and currently about 25 families of frogs including such groups as gold frogs, true toads, ghost frogs, Old World tree frogs, African tree frogs, spadefoot toads, and many others.

The earliest known frog-like ancestor is Gerobatrachus, a toothed amphibian that lived about 290 million years ago. Another early frog was Triadobatrachus, an extinct genus of amphibian that dates back 250 million years. Modern adult frogs and toads have four legs but do not have tails, and many frog species have evolved the ability to poison predators that touch or taste their skin.

Caecilians

Black caecilian

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Caecilians are the most obscure group of amphibians. They have no limbs and only a very short tail. Their name derives from the Latin word for "blind" because most caecilians have either no eyes or very tiny eyes. Caecilians live in the tropics of South and Central America, Africa, and southern Asia. They live mainly on earthworms and small underground animals.

While caecilians bear a superficial resemblance to snakes, worms, and eels, the are not closely related to any of those species. The evolutionary history of caecilians remains obscure and few fossils of this group of amphibians have been discovered. Some scientists suggest that caecilians arose from a group of tetrapods known as the Lepospondyli.