Amphibian
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What Is an Amphibian?
Amphibians are animals in the class Amphibia. Their young usually live in water, while adults often live on land. The word “amphibian” comes from Greek words meaning “both lives,” because these animals spend part of their life in water and part on land. Today, there are about 5,700 different species of amphibians.
A Brief History of Amphibians
- Origins (Devonian Period, ~390 million years ago): The first four-legged animals with simple lungs appeared in water. These early amphibians had gills, a backbone, and a tail.
- Life on Land (Carboniferous Period): As plants and other animals competed for space in water, amphibians developed stronger legs and lungs so they could move between ponds and streams.
- Size and Success: Amphibians ranged from giants like the 15-foot Ichthyostega and 6-foot Eryops down to tiny frogs under 1 cm long. They thrived in diverse environments—from deserts to icy regions—and remained among Earth’s top animals for about 75 million years.
How Amphibians Are Classified
| Order Name | Common Name | Approx. Number of Species |
|---|---|---|
| Anura | Frogs and toads | ~5,070 |
| Caudata (Urodela) | Salamanders | ~510 |
| Gymnophiona (Apoda) | Caecilians (worm-like) | ~170 |
All living amphibians belong to Lissamphibia, which includes: Anura (frogs and toads), Caudata or Urodela (salamanders), and Gymnophiona or Apoda (caecilians).
The Amphibian Life Cycle
- Grow four legs for walking on land
- Replace gills with lungs to breathe air
- Develop skin glands to stay moist
- Form eyelids and ears to see and hear on land
5 interesting facts about amphibians
1. Amphibians can breathe through their skin, which must stay moist to absorb oxygen.
2. Frogs can jump up to 20 times their body length in a single leap.
3. Amphibians undergo metamorphosis—from larvae (like tadpoles) to adults.
4. Some salamanders can regrow lost limbs, tails, and even parts of their heart or eyes.
5. Amphibians are cold-blooded and rely on their environment to regulate body temperature.
The most obvious part of the amphibian metamorphosis is the formation of four legs in order to support the body on land. But there are several other changes:
- The gills are replaced by other respiratory organs, e.g. lungs.
- The skin changes and develops glands to avoid dehydration
- The eyes get eyelids and adapt to vision outside the water
- An eardrum is developed to lock the middle ear
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