Why Amphibians are Unique in the Animal World

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"Why Amphibians are Unique in the Animal World"
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It is all too easy to underestimate the humble amphibian. Frogs, toads, newts and salamanders (also Caecilians!), they are small, seldom seen and often slimy. In reality, the ancestors of these animals were the first to crawl from the water onto land and the fascinating life history of amphibians preserves a record of this in many ways. As animals they are unusual in being 'biphasic', having an aquatic stage and a terrestrial stage.

Amphibians first colonized land during the Devonian era, some 350 million years ago. In the immense period of time since then they have developed huge variations in order to fit into the differing ecological niches of the world. They have spread to almost every area of the globe. As a result few characteristics are common to absolutely all of them.

Typically though, amphibians are unique amongst animals because their lives go through an egg, larva and adult stage. They begin life as an egg laid in water and fertilized externally ( there are a few exceptions) and after hatching live and grow as a larva in water. Gradually during this stage they metamorphose into miniature adults. This involves changing from breathing through gills to breathing through lungs, growing limbs, and developing a skin able to withstand exposure to air. Amphibian skin is unique in being naked, without hairs, scales of feathers but having mucous glands. These developmental stages of the amphibian larvae are undergone by other animals before birth.

Most amphibians live on land as adults, but are quite at home in water. Some can swap from land to water and adapt and readapt to each environment. Nearly all amphibians return to water to breed and lay eggs which need to absorb water to develop and hatch (Amamniotic eggs). As an Order these are facinating animals which deserve to be better understood and maybe even loved a little!

More about this author: Mark Hopkins

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