The 3 Basic Amphibian Groups

A Beginner's Guide to Amphibian Classification

Salamandra salamandra
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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. They were the first vertebrates to make the move from life in water to life on land. Despite their early colonization of terrestrial habitats, most lineages of amphibians have never fully severed their ties with aquatic habitats. In this article, we'll take a look at three groups of amphibians, their characteristics and the organisms that belong to each group.

Amphibians are one of the six basic animal groups. Other basic animal groups include birds, fish, invertebrates, mammals, and reptiles.

About Amphibians

A Tree Frog Looks Content Sitting On A Tree Branch
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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.
  • They have many different ways of reproducing; some lay eggs, some bear live young, some carry their eggs while others leave their young to fend for themselves.
  • Amphibians can breathe and absorb water through their thin skin.

Newts and Salamanders

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

Frogs and Toads

Red-eyed tree frog - Agalychnis callidryas
Photo © Alvaro Pantoja / Shutterstock.

Frogs and toads belong to the largest of the three groups of amphibians. There are more than 4,000 species of frogs and toads alive today. 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.

There are 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. Many frog species have evolved the ability to poison predators that touch or taste their skin.



Black caecilian - Epicrionops niger
Photo © Pedro H. Bernardo / Getty Images.

Caecilians are the least-known group of amphibians. Caecilians have no limbs and only a very short tail. They have a superficial resemblance to snakes, worms, or eels but are not closely related to any of these animals. 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.

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