Amphibians are vertebrates (animals with backbones) who were actually the first four-limbed vertebrates to walk the Earth. They are cold-blooded, with their body temperature being regulated by their surrounding temperature. They spend part of their lives in water and part on land, which is how they earned their name of “amphibian”, from the Greek word meaning “double life”.
There are three groups of amphibians, defined by their orders: frogs and toads (Anura), salamanders and newts (Caudata), and burrowing legless and wormlike caecilians (Gymnophiona). There are actually 73 families and 7,292 species of amphibian in the world, but many are not as well known. Let’s deconstruct what is an amphibian and look at these animals in greater detail below.
Amphibians are known for their damp smooth skin and lack of scales, feathers or hair. Their moist skin is kept this way by special glands under the surface of the skin that produce a sticky substance called mucus.
The skin is also permeable, meaning air can pass through the skin, and many amphibians therefore breathe through their skin instead of through their lungs. They are born with gills, with some outgrowing them as they transform into adults, and others retaining them for their entire lives. As blood flows through an amphibians gills at the same time water flows over the outside, oxygen passes out of the water straight into the bloodstream.
Toads and frogs have flattened skulls, and also short backbones and enlarged hind legs. Salamanders and newts have longer backbones than toads and frogs, and their limbs are all roughly the same size. They also have long tails, with newts having a flattened tail that makes them excellent swimmers.
As they are cold-blooded (ectothermic), an amphibian’s body temperature is regulated by the temperature around them. They have a 3 chambered heart, not 4 as in mammals, and have far fewer bones than those of other vertebrate species.
Amphibians have 5 basic senses, taste, hearing, smell, sight and touch, just like humans. However, they can also detect the Earth’s magnetic field and infrared and ultraviolet light.
Amphibians color varies. Most are brightly colored, which helps to warn potential predators to stay away. Some also change the color of their skin, which is a response to temperature changes. Not only this, but some, such as snakes and lizards, shed their skin, which helps to keep their skin healthy.
Amphibians are carnivores and feast on smaller prey, such as insects and worms. However, bigger species, such as frogs and toads, may eat other backboned animals like mice, birds and small reptiles. Many have large mouths to feed and one of these meals will satisfy their appetite for a good period of time and give them enough energy.
Amphibian larvae eat aquatic invertebrates, but can also sometimes become cannibalistic and eat their own kind.
Amphibian Reproduction and Life Cycle
Amphibians breed in the spring and lay eggs that are jelly-covered, called spawn, in still, fresh water, often among water plants. The young are called tadpoles and can only live in water. These aquatic larvae have feathery, external gills and tails, but soon develop lungs and legs by metamorphosis and leave the water.
Amphibian eggs lack a shell, so parental protection is important and common among most species of amphibians. In caecilians, newts and salamanders, the female usually provides protection whereas in frogs and toads, the male protects the eggs from predators. However, some species do not protect their young at all, and others are protected by both parents.
Adults are able to live both in water and on land. At the the larval stage, they can only live in water. However, at the adult stage, amphibians spend most of their life on land, usually in damp habitats like woods, only returning to the water to breed in the spring. More than 75 percent of all toad and frog species in the world live in tropical rainforests. A few species may be found in water at almost any time of year. Some like to live in drier grasslands and even the deserts.
Amphibians live all over the world, aside from high Arctic, Antarctica and remote islands. They can only live in freshwater, and never saltwater.
Because of their special skin, they require very specific living conditions. Too much sun can damage their cells, and too much wind can dry their skin and dehydrate them. As a result, amphibians are very susceptible to their habitats being disturbed or contaminated with chemicals like weed killers. This is the main reason over half of all frog species are in danger of extinction.
Summary Of Amphibian Fun Facts!
- The endangered Chinese giant salamander is the world’s largest amphibian, and can measure as long as 1.3 meters!
- The word ‘amphibian’ comes from the Greek word ‘amphibios’ meaning ‘double life’ as these animals are able to live both on land and in water.
- They were the first land animals and have kept close links to water where their ancestors originated.
- When the weather turns very cold, they hibernate by burying themselves in the mud at the bottom of ponds or under stones or logs.
- They have been around for around 230 million years and are known to have evolved from fish.
- They bask in the sun to warm-up and enter the water to cool down. Amphibians have smooth skin, 4 limbs and are divided into 3 groups:
- Frogs and Toads
- Frogs and Toads can eat large animals such as mice, birds, small reptiles and small snakes.
- Sometimes larvae can become cannibalistic and consume their own kind.
- They are typically aquatic as larvae and terrestrial as adults.
- No amphibians inhabit salt water (oceans and seas).
- Amphibian eggs generally lack shells and all are produced in water.
- Larval gills are lost and replaced by air-breathing lungs and in the case of frogs and toads, their tails (which they have as tadpoles) are reabsorbed and they develop limbs.
Facts about amphibian anatomy
- Amphibian skeletons have far fewer bones than those of other vertebrate species.
- They have a 3 chambered heart, not 4 as in mammals.
- Amphibians have 5 basic senses, taste, hearing, smell, sight and touch, just like humans. However, they can also detect the Earths magnetic field and infrared and ultraviolet light.
- Toads and Frogs (order: Anura) have flattened skulls. They also have short backbones and enlarged hind legs.
- Salamanders and Newts (order: Caudata/Urodela) have longer backbones than toads and frogs. Their limbs are roughly the same size and they have long tails.
- Newts have flattened tails which makes them excellent swimmers.
- Caecilians (order: Gymnophiona) have no limbs and move along by muscle contractions that move along their body.
- Caecilians have a tentacle on each side of the head located between the eye and the nostril. The tentacles are used as scent detectors to locate prey.
- Some such as snakes and lizards shed their skin.