What are Amphibians?

Michael Anissimov
Michael Anissimov

An amphibian is any non-amniotic (lacking eggs with a shell), cold-blooded, tetrapod animal that spends at least part of its time on land. Living examples include frogs, toads, salamanders, newts, and caecilians. There are only about 6,200 living species described by science, but there are many extinct amphibians in the fossil record. Of the three subclasses of amphibians (Labyrinthodonti, Lepospondyli, Lissamphibia), only one, Lissamphibia, is extant. Amphibians are much less successful today than in the geologic past, having been outcompeted by reptiles and mammals.

Amphibians, like tree frogs, are non-amniotic, cold-blooded tetrapods who spend at least part of their life on land.
Amphibians, like tree frogs, are non-amniotic, cold-blooded tetrapods who spend at least part of their life on land.

Amphibians are animals that move in and out of the water. Lacking scales like reptiles, they are more prone to drying out, and so most species require frequent dips to stay moist. Except for a few frog species, these animals are dependent on pools of fresh water to lay their eggs in. These eggs sit in the water, with some entering into symbiotic relationships with unicellular algae. After a few days, these eggs hatch into tadpoles, the larval form of frogs, which swim through the water, eating detritus. Through a process called metamorphosis, these tadpoles transform into adult frogs.

A salamander is an amphibian.
A salamander is an amphibian.

These animals are most closely related to mammals that still have a larval stage. Other tetrapods go through their larval stage in the egg or womb and emerge as small versions of the adult form. This can be seen in some tropical frogs, which lay their eggs on the forest floor, and hatch in a miniature adult form.

Newts are a type of amphibians.
Newts are a type of amphibians.

The first amphibian was also the first tetrapod. An animal that lived about 365 million years ago, Acanthostega, is usually cited, though there were several early tetrapods that lived around the same time. Acanthostega resembled a salamander, with eight digits on each limb. It is thought that limbs initially evolved to get through root-choked swamps, and eventually became strong enough to use for forays on land. For their combination of fish and tetrapod characteristics, some of the earliest land animals have been referred to as fishapods. For about 25 million years, amphibians were the only tetrapods and land vertebrates, until the evolution of amniotes (reptiles) with animals like Casineria, which lived 340 million years ago.

The earliest true amphibians, called temnospondyls, were typically 1.5 to 5 feet long and the first tetrapods to walk on land.
The earliest true amphibians, called temnospondyls, were typically 1.5 to 5 feet long and the first tetrapods to walk on land.
Toads are amphibians.
Toads are amphibians.
Michael Anissimov
Michael Anissimov

Michael is a longtime wiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments


@DylanB -- I also love the tree frogs. Once they attach themselves to the window, they don't move much, but they are fascinating to look at.

I had a tree frog that got inside the house once. I discovered him down in the basement and he was alive but looked pretty dry and shriveled up. He wasn't moving around so I put him in a jar with a little bit of water in it. Once he was revived, I placed him back outside where I hope he lived for a long time.

I have always wondered what is the lifespan of a frog or toad? Do they live for just one season or longer than that?


We have toads that like to hang out around our basement steps. I don't really mind them since I know they eat a lot of bugs. If they start hopping around, my dogs like to chase them, but they found out they don't taste very good. Once one of my dogs tried to eat one and must not have cared for the taste at all. It doesn't seem like you see nearly as many toads and frogs as you used to, but I know they are good for the overall ecological system.


I grew up in the city and have lived there my whole life. I feel just the opposite when it comes to the sounds of the frogs at night. When I visited a friend in the country, I wondered what could cause such a loud ruckus at night.

I was surprised to find out it was from all the frogs. Since I wasn't used to this sound I found it to be loud and annoying. If I had kept my window open, I think they would have kept me up all night.


@seag47 -- Even as a young girl I loved the summer night sounds. For me this is a soothing, comforting sound and because of that, I love to sleep with my windows open in the summer. Nothing puts me to sleep better than listening to the sounds of the frogs. We have a large pond in our yard, so I get to listen to this chorus all summer long.

I also enjoy watching the transformation of the tadpoles into frogs throughout the summer. When you look into the pond in the spring or early summer, you see all sorts of tiny tadpoles swimming around.

Gradually as the season progresses they get bigger and bigger, and start to resemble a full grown frog. I have always been fascinated by this and enjoy watching this happen every year.


@DylanB – I know what you mean. I live next to a pond, and the frogs really take over the atmosphere at twilight!

The loudest amphibian in my yard is the bullfrog. It has this really low bellow that is quite scary if you don't know where it's coming from.

So, I have a mixture of deep-voiced bullfrogs and cute little high-pitched tree frog sounds filling the air. It's cool how they all start at about the same time of day, right after sunset.


The tree frog is the most fascinating amphibian to me. I love it when one of these frogs attaches itself to my window by the little suction cups on its feet, and I can watch its neck skin moving rapidly as it breathes.

These frogs can blend into their environment really well. I once saw one on concrete, and I thought it was just a lump! When I touched it, it felt slimy and squishy, and I screamed.

Tree frogs sure do make a lot of noise, though. I am glad that they simmer down by the time I go to bed, or I would have trouble sleeping.


@shell4life – Snakes are reptiles, not amphibians. They do spend time in water, but so do other reptiles like alligators.

They don't lay their eggs in water like amphibians do. Different snakes reproduce different ways. Some have nests on land, and some give live birth.


Are snakes amphibians or reptiles? I've seen several that spend a lot of time in water, and I believe that they are cold-blooded. I don't know anything about how they reproduce, so I'm unsure of how they should be classified.


@oceanswimmer: The turtle is a reptile. There are ways to distinguish between reptiles and amphibians. The first thing is to determine whether or not there are scales. Reptiles have scales. They can be smooth or rough, large or small. Reptiles also have a tough outer covering. That helps them to conserve water and has allowed the animal to spread across terrestrial habitats in a way in which amphibians would not be able to.

Amphibians generally have soft, smooth skin. It is very porous and several of the amphibians breathe through their skin.

Also, reptiles have claws and amphibians do not.


@oceanswimmer: First of all, no question is a crazy question. We only learn by asking questions. Now, to answer your question: Turtles are not amphibians. They are actually reptiles.


I know this might sound like a crazy question but are turtles amphibians?


Well done wisegeek, we were just wondering what a newt was and you have answered our queries perfectly, thank you

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