Temporal range: Triassic – Recent
|White's Tree Frog (Litoria caerulea)|
|Distribution of frogs (in black)|
Frogs are amphibians of the order Anura. There is no fundamental difference between frogs and toads, and they are not classified separately. This is because the toad lifestyle, with its dry, rough, skin, is an adaptation to living in drier habitats. The toad form has evolved a number of times independently, an example of convergent evolution.
Frogs can live on land and in fresh water. They cannot survive in salt water. Their development is by metamorphosis. They hatch as tadpoles from eggs, which are laid by a female frog. The eggs are called frogspawn. Tadpoles have tails and gills. When they grow up, they lose their tails and gills and grow four long legs.
Adult frogs can jump with their legs. They have long tongues that they use to catch bugs. They make a sound called a croak. Some species live in trees, and some types of frog are protected by being poisonous. Frogs live all over the world. If an overseas species of frogs is introduced to another country, the ecosystem might be affected.
Frog legs are occasionally eaten as food in France, China, and the Midwest of the United States. The killing of frogs might have an effect on the ecosystem. For example, frogs eat mosquitoes. If frogs are killed, then there are fewer frogs to eat mosquitoes, so more and more mosquitoes are born. Therefore, in these areas, there are more diseases that mosquitoes carry, because there are more mosquitoes. However, for this to apply, frogs would have to be a major predator of mosquitoes. This would only rarely be the case.
Amphibians are four-legged vertebrates. This means that they have backbones. A backbone is made up of smaller bones called vertebrate. They are similar to reptiles because they are cold blooded animals. This means that they need heat to maintain body temperature. If the temperature outside is cold, amphibians will not be active. They will stay like this until the temperature rises. However, most amphibians lay their eggs in foam nests and not shells. Amphibians take in heat through their wet skin. Amphibians can get heat from the sun or through a lightbulb in captivity by their owners.
Many amphibians will hibernate during winter in places where it gets very cold. These amphibians will hide in an underground place to hibernate. These include hibernating underwater and burrowing in muds and holes. They can breathe underwater as long as they can get oxygen through their skin. They will come out of hibernation when the weather outside is warm. Sometimes they will come out of hibernation if its raining to drink water, but will go back to hibernating once they are done. Amphibians has thin skin with no scales or hair. They can take in oxygen from either water or air. Amphibians create mucus that helps their skin to stay wet and slippery. They sometimes use their lungs when they are active or need more oxygen. Many amphibians have toxic skin. They have secretions which makes their skin poisonous.
Most amphibians are semi-aquatic, this means that they need to be in the water more often. They are also able to live on both land and in water. Ranidae frogs, some Hylidae frogs, Bombinatoridae toads, Ascaphidae frogs, Pipidae frogs and all newts and salamanders are all semi-aquatic amphibians. These amphibians likes to swim or float on top of an aquatic plant. Some can be seen near plants in the water, they do this to hide from any predators who may want to eat them. Their entire body will be underwater, while their eyes will be watching for any predators. Most amphibians like to live in warm slow moving freshwater. These include ponds, swamps, rivers and lakes. Others like to live in cold fast-moving waters. These include creeks and streams. Most adult amphibians will stay near the water where they grew up in. They will also stay near water to keep their skin wet.
- Zweifel, Richard G; Cogger H.G. & Kirshner D. 1998. Encyclopedia of reptiles and amphibians. San Diego: Academic Press. pp. 91–92. ISBN 0-12-178560-2
- Carroll, Robert 2009. The rise of amphibians: 360 milion years of evolution. Johns Hopkins University Press, Baltimore. Chapter 10: The ancestry of frogs. ISBN 978-0-8018-9140-3
- Morgan 2004, p. 4.
- Richardson 2006, p. 6.
- Morgan 2004, p. 5.
- Stebbins 2003, p. 200.
- Grenard 2007, p. 18.
- Grenard 2007, p. 22.
- Morgan 2004, p. 6.
- Morgan 2004, p. 7.
- Theodorou 2007, p. 5.
- Grenard 2007, p. 7.
- Campbell 1999, p. 22.
- Royston 2004, p. 5.
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