Amphibians are some of the most fascinating creatures on Earth, bridging the gap between water and land with unique adaptations. Understanding amphibian traits can help students grasp key biological concepts like life cycles, metamorphosis, and environmental adaptations. Whether you’re teaching about frogs, salamanders, or caecilians, exploring what makes amphibians special is a great way to spark curiosity about the natural world.
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What Are Amphibians?
Before we dive into the traits of amphibians, it helps to answer the question “what are amphibians?”. Amphibians are a group of vertebrates—animals with backbones—that share some key traits. There are seven classes of vertebrates on Earth: amphibians, birds, mammals, reptiles, and three types of fish.
But how do scientists know which animals belong in each class? It all comes down to family trees! Each class of vertebrates shares a common ancestor from long ago. If you traced their lineage back far enough, you’d find that all amphibians—frogs, salamanders, and more—descend from the same ancient relative. That’s why a salamander is more closely related to a frog than to a reptile like a lizard.
Thanks to their shared lineage, amphibians share some characteristics. In this post, we’ll discover some key amphibian traits…
A Backbone
Like all vertebrates, amphibians must have a backbone. A backbone is actually made of many individual, smaller bones called vertebrae, all stacked up in a flexible column. Amphibians’ spines help us tell them apart from invertebrate (backbone-less) creatures like insects and mollusks.
Cold-Blooded
Ever wonder why you see a frog sitting out on a lily pad in the sun? Amphibians are cold-blooded or ectothermic animals, which means their body temperature depends on the temperature of the air or water around them. They must rely on external (outside of themselves) heat sources to stay warm rather than making their own body heat.
When amphibians need to warm up, they sun themselves. If they get too hot, they go into cool water, underground, or find shade. Because they rely on external heat sources, their temperature varies a lot. Amphibians, reptiles, and most fish are cold-blooded animals.
Moist, Permeable Skin
One of their most distinctive features is their moist, scale-free skin. Amphibians, even the ones that look bumpy, like toads, never have scales. This is one of the key differences between amphibians and reptiles.
To stay hydrated, amphibians usually live in damp environments or near water. Their skin contains special mucus glands to keep it moist. It’s also permeable, allowing water and gases to pass through. This means amphibians can absorb water and even breathe through their skin! However, most species also have lungs or gills for breathing.
Metamorphosis
Another trait of amphibians is metamorphosis—a dramatic transformation during their life cycle. For example, a tadpole with gills and a tail changes into an adult frog with lungs and legs.
Most amphibians go through metamorphosis, but there are a few types of amphibians that are exceptions. Some species of caecilians, a group of legless amphibians, develop differently and don’t go through metamorphosis the way frogs and salamanders do.
Carnivorous
Finally, all adult amphibians are carnivores. Often, they hunt and eat small invertebrates – little animals without a backbone – like insects and worms. However, some large amphibians like bullfrogs will even hunt small vertebrates like smaller amphibians, reptiles, and even mammals like mice.
While adult amphibians are carnivores, larval amphibians often are not. This is because before going through metamorphosis, they are more suited to eating plant matter. For example, a tadpole lives in a pond and eats plant matter before it grows up into a frog that eats insects.
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References and Further Reading
- Clark, M.A., Douglas, M., and Choi, J. (2018). Biology. Open Stax. Ch 29.3. Available: https://openstax.org/books/biology-2e/pages/29-3-amphibians
- Fowler, S., et al. (2013). Concepts in Biology. OpenStax. Ch 15.6. Available: https://openstax.org/books/concepts-biology/pages/15-6-vertebrates
- San Diego Zoo (n.d.). Salamander and Newt. Available: https://animals.sandiegozoo.org/animals/salamander-and-newt
- Wake, DB and Koo, MS. 2018. Primer: Amphibians. Current Biology 28(21): R1237-R1241. https://doi.org/10.1016/j.cub.2018.09.028