Amphibians are a class of animals like reptiles, mammals, and birds. They live the first part of their lives in the water and the last part on the land. When they hatch from their eggs, amphibians have gills so they can breathe in the water. They also have fins to help them swim, just like fish. Later, their bodies change, growing legs and lungs enabling them to live on the land. The word "amphibian" means two-lives, one in the water and one on land.
Amphibians are Cold-blooded
Like fish and reptiles, amphibians are cold-blooded. This means their bodies don't automatically regulate their temperature. They must cool off and warm up by using their surroundings.
Growing up from Egg to Adult
Most amphibians hatch from eggs. After they hatch, their bodies are still in the larvae stage. In this stage they are very fish like. They have gills to breathe under water and fins to swim with. As they grow older, their bodies undergo changes called metamorphosis. They can grow lungs to breathe air and limbs for walking on the ground. The transformation isn't the same in all amphibians, but most species go through some sort of metamorphosis.
Stages of a Frog
As an example of metamorphosis, we will look at the frog:
Source: Meyers, pd
a) after hatching the frog is a tadpole with a tail and gills
b) it becomes a tadpole with two legs
c) a tadpole with four legs and a long tail
d) a froglet with a short tail
e) a full grown frog
Types of Amphibians
Frogs - Frogs are amphibians of the order anura. They generally have a short body, webbed fingers and toes, bulging eyes, and no tail. Frogs are good jumpers with long powerful legs. Toads are a type of frog. Two species of frogs are the American bullfrog and the poison dart frog.
Salamanders - Salamanders look a bit like lizards. They have skinny bodies, short legs, and long tails. Salamanders can re-grow lost limbs and other body parts. They like wet, moist areas like wetlands. A newt is a type of salamander.
Caecilians - Caecilians are amphibians that don't have legs or arms. They look a lot like snakes or worms. Some of them can be long and reach lengths of over 4 feet. They have a strong skull and a pointed nose to help them burrow through dirt and mud.
Where do they live?
Amphibians have adapted to live in a number of different habitats including streams, forests, meadows, bogs, swamps, ponds, rainforests, and lakes. Most of them like to live in or near water and in damp areas.
What do they eat?
Adult amphibians are carnivores and predators. They eat a variety of food including spiders, beetles, and worms. Some of them, like frogs, have long tongues with sticky ends that they flick out to catch their prey.
The larvae of many amphibians mostly eat plants.
Northwestern Salamander Source: USFWS
Big and Small
The largest amphibian is the Chinese Giant Salamander. It can grow to 6 feet long and weigh 140 pounds. The largest frog is the Goliath Frog which can grow to 15 inches long (not counting the legs) and weigh over 8 pounds.
The smallest amphibian is a frog called the paedophryne amauensis. It is also the world's smallest vertebrate animal. It is about 0.3 inches long.
Fun Facts about Amphibians
Most amphibians have thin, moist skin that helps them to breathe.
Amphibians are considered vertebrates as they have a backbone.
Frogs swallow their food whole. The size of what they can eat is determined by the size of their mouths and their stomach.
Frogs cannot live in salt water.
All amphibians have gills, some only as larvae and others for their entire lives.
It is a myth that you can get warts from touching a frog or toad.
A group of frogs is called an army.
An Amphibian's skin absorbs air and water. This makes them very sensitive to air and water pollution.