Why Are Frogs Amphibians?

Frogs are incredibly fascinating creatures with plenty of unique skills, abilities, and physical characteristics. It’s well-known that they have been classified as amphibians, but many people wonder why they belong to the amphibian class rather than the reptile class. 

Amphibian means “double life” or “two lives” and the Tetrapoda of frogs is Amphibia because frogs live part of their lives in water as tadpoles, and part of their lives on land as froglets and adult frogs.

Frogs are infamous for their remarkable jumping and climbing abilities, croaking, slimy skin, and bulging eyes. Amphibians are quite versatile, and they differ from similar animal classes such as reptiles. Join us as we discuss what it means to be an amphibian and why frogs suit the group so well. 

What Does “Amphibian” Mean?

The word ‘amphibian’ is derived from a Greek word that translates to “double life” or “two lives.” All amphibians live their lives both on land and in water. Frogs and toads make up 88% of amphibians with over 7,400 recorded species according to Amphibaweb. 

Because of the frog’s complex life cycle that begins in water and transitions into the ability to live on land, they can be classified as amphibians. Amphibians are cold-blooded vertebrates, meaning that their bodies are the same temperature as their environment, whether dwelling in water or on land. 

Their bodies adjust to the air or water temperature, and they will bask in sunlight to heat up when they get cold. By contrast, they may find a space to cool off in shady spots or water, or the sun gets too warm. 

Amphibian Classification & Taxonomy

Here is the full classification and taxonomy of amphibians:

ClassificationFrogs
KingdomAnimalia
Subkingdom Bilateria 
Infrakingdom Deuterostomia 
Phylum Chordata
SubphylumVertebrata
InfraphylumGnathostomata 
SuperclassTetrapoda 
Tetrapoda Amphibia  
OrderAnura
Family54 families 
GenusOver 300 genera
Species Over 7,400 species

Characteristics of Amphibians

Amphibians are cold-blooded (ectothermic), can live on and in water, they have no scales on their porous skin, they breed in water and their larval stage has a tail, they have no neck and can breathe through their skin and lungs as adults.

Here are common characteristics of all amphibians:

  • Cold-Blooded (Ectothermic)
  • Can Live on Land
  • Can Live in Water
  • Larval Stage Has Tail
  • Skin Has No Scales
  • Three-Chambered Heart
  • Breeds in Water
  • Has No Neck
  • Adults Breathe Through Skin And Lungs
  • Glands to Keep Skin Moist

Frogs are not the only amphibians, although they are the most well-known and the most numerous. Various unique and interesting animals belong to the amphibian class, with both similar and varying physical characteristics. 

Differences Between Frogs & Other Amphibians

Although frogs are amphibians, they are very different from salamanders and newts and caecilians.

Frogs are classified as Anura within the Amphibian family because frogs:

  • Have no tail as adults
  • Have forelimbs shorter than hindlimbs as adults
  • Have excellent vision
  • Have an external tympanum
  • Have bulging eyes
  • Reproduce externally by amplexus

These key distinguishing characteristics can help you differentiate frogs from other amphibians. There are three types of species within the Amphibian Tetrapod. Let’s have a look at these types of amphibians and how many are in each group (CTNF).

Types of Amphibian Species by The Numbers

Frogs and toads (Anura) make up 88% of amphibians as of September 2021 with over 7,400 recorded species according to AmphibiaWeb. Salamanders and newts (Caudata), and caecilians (Gymnophiona) respectively make up 9% and 3% of known amphibian species.

The following amphibian species numbers have been documented as of September 2021 according to AmphibiaWeb:

OrderAmphibiansNumber of SpeciesPercentage
Anura Frogs, Toads7,40188%
Caudata Salamanders, Newts7659%
Gymnophiona Caecilians2153%

Frogs greatly outnumber the other types of amphibians. Many websites provide very different numbers but I always use AmphibiaWeb to track the number of known frog species since they tend to have the most up-to-date information available on the web at any given time.

New frog, toad, newt, salamander, and caecilian species are discovered every month so depending on when you read this article the numbers will probably have increased, but generally, there are much more toads and frog species than the other amphibians.

Differences Between Amphibians & Reptiles

It’s quite common for amphibians and reptiles to be confused with each other. Although these two animal classes do have some similarities, there are many differences. These differences ultimately contribute to frogs being classified as amphibians and not reptiles. 

Both amphibians and reptiles hatch from eggs and are ectothermic creatures, meaning that they lack an internal thermostat and need to use external influences to control their temperature. The two animal classes are often grouped together, referred to as herpetofauna. 

Key differences between reptiles and amphibians are as follows:

CharacteristicAmphibiansReptiles 
Cold-Blooded (Ectothermic)YesYes
Can Live on LandYesYes
Skin Has ScalesNoYes
Three-Chambered HeartYesYes
Can Live in WaterYesNo
Larval Stage Has TailYesNo
Breeds in WaterYesNo
Jelly-Like EggsYesNo
Breathes Through Skin And LungsYesNo
Glands to Keep Skin MoistYesNo

The primary differences between amphibians and reptiles concern their life cycle. Amphibians have a complex life cycle, spending time in water and on land. Some reptiles spend time on land and in water, but their physical properties generally remain the same as they age.

After reading that you may be confused about the difference between turtles and frogs since turtles can live in water. Turtles are classified as Reptiles because, contrary to Amphibians, turtles have scaly skin, a long neck, fertilize their eggs internally, do not breed in water, and their hind legs are not long or made for jumping.

Amphibians have permeable skin that they use for breathing. Since amphibians mainly use their skin to breathe, amphibians need to remain hydrated and moist. As a result, amphibians do not have scales, although they may have bumps, ridges, and textured skin within some species. 

Reptiles only breathe through their lungs, which leads to many key differences in their physical traits. They have rough, scaly, and dry skin that prevents their internal workings from becoming dehydrated. Their scaly skin is far more protective against pollutants and environmental threats, meaning some reptiles can live in saltwater (whereas most frogs cannot).

Amphibian Origins & Survival

Scientists have found frog fossils that date back as far as 200 million years ago, placing these amphibians in the Jurassic period. Frogs have stood the test of time, acting as predators and prey within nature’s circle of life. 

Scientists use amphibians, especially frogs, for insight into an ecosystem’s health. But, amphibians are the most threatened of all animal classes in nature. This is since they are incredibly vulnerable and sensitive to environmental threats due to their permeable skin and porous eggs. 

Frogs are affected by numerous environmental issues, including pollution, fungus, climate change, and disease. Many amphibians, particularly unique frog species, are traded internationally and domestically to be sold as exotic pets. Some cultures hunt amphibians for food, adding more threats to an already challenging situation. 

Amphibian habitats have become incredibly small and complex compared to many years ago, being taken over by human activity and modernization. Experts are calling this occurrence an ‘amphibian apocalypse’, which demands the aid of animal lovers and amphibian enthusiasts. Thankfully, numerous organizations are dedicated to preserving the lives of these innocent amphibians. 

Thankfully, you can easily help your local amphibians in your own backyard by making your yard toad and frog friendly and by creating a hibernaculum to help toads hibernate in winter.

More About Amphibians And Frogs

Frogs are fascinating amphibians that make up the vast majority of this classification. Learn more about frogs, toads, and how you can help them by reading the following articles on our blog:

Sources 

Laurie J. Vitt, Janalee P. Caldwell, Chapter 17 – Frogs, Editor(s): Laurie J. Vitt, Janalee P. Caldwell, Herpetology (Fourth Edition), Academic Press, 2014, Pages 471-522, ISBN 9780123869197, https://doi.org/10.1016/B978-0-12-386919-7.00017-4.

Helmer Peter J., Whiteside Douglas P., Amphibian anatomy and physiology, Science Direct, 2005.

AmphibiaWeb, 2021, Amphibian Species by The Numbers, University of California, Berkeley, CA, USA, Retrieved September 1, 2021