Al animals are classified or separated into special groups. Some of the special groups include mammals, bird, fish, and reptiles. Other groups may include cold-blooded, warm-blooded, vertebrates, invertebrates, and several others. One group of animals that are known for their ability to live both in water and on land are called amphibians. The word amphibian comes from a Greek word meaning 'double life'.
There are about 7,000 species of amphibians living in the world surviving on land and in water. They are an ancient group of animals that descended from fish and first appeared about 340 million years ago. Some of them have legs but others have no limbs. Amphibians have vertebrates or backbones just like humans; however, amphibians are cold-blooded, and humans are warm-blooded. They are not in the same animal group.
The most popular amphibians are frogs and toads such as the American Bullfrog, Poison Dart Frog, American Toad, Tomato Toad, and many more. Others include salamanders and newts. All amphibians have several common characteristics too.
Their vertebrates are like human's but much smaller, and the backbone is part of the exoskeleton, which means bones inside the body giving the amphibian its shape and support. And part of their lives they live on land, but they also live in or near water, and they use gills while in the water. The gills help them breathe. Later, they will grow lungs and legs which will help them live on land.
In addition, as it is cold-blooded, the amphibian's body temperature changes with its environment. For example, if the air temperature is 58° F, the amphibian's body temperature will be the same. Compared to humans, whose body temperature always stays the same at 98° F.
Adult amphibians must stay near the water to keep their skin wet and they do not drink water. Instead, water is absorbed through their skin. Another characteristic of amphibians is their webbed feet for help when they need to swim in the water.
Amphibians are hatched from eggs and look very different than their parents. They have no legs when they are born but will later change, but as adults, they will look like their parents. Though all amphibians have common characteristics, frogs and toads lose their tails as adults, but salamanders keep their tails when they become adults. They look like lizards without scales, and if they lose one of their limbs, it will grow back or regenerate.
Following birth, amphibians look like fish and nearly all go through a transformation or change called metamorphosis. For example, a frog hatches as a tadpole with a tail and gills; becomes a tadpole with two legs; develops four legs and a long tail; then becomes a froglet with a short tail; and then finally becomes a full-grown frog.
Amphibians live in a wide range of habitats, with most of them living in or near water such as streams, forest, meadows, lakes, ponds, swamps, and other damp or wet areas. They like to eat beetles, worms, and spiders, and some frogs have a long, sticky tongue they use to catch prey.
They come in all sizes from the Chinese Giant Salamander at 6 feet and 140 pounds to the smallest frog in the world which is about 0.3 inches long, the width of a pinky finger. Finally, sometimes frogs and toads may appear the same, but fogs have smooth, moist skin and longer legs than toads. On the other hand, toads have dry, bumpy skin and short legs since they walk more often than they hop.
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