Amphibians and reptiles are both generally cold-blooded vertebrates that each date back more than 300 million years. While they share some similarities, there are even more differences that set them apart from one another. When we analyze certain factors – such as habitat, lungs, and reproduction, among others – the distinctions between these two species groups become much clearer!
Amphibians and reptiles are both cold-blooded, tetrapod vertebrates. Both originating more than 300 million years ago, the evolution of each has resulted in vast differences between them, despite some commonalities. From their evolution to their modern-day physiology, there are numerous factors that distinguish amphibians from reptiles.
In order to fully understand the differences between amphibians and reptiles, you need to know more about each. Understanding the origin and characteristics of each of these species will allow you to better compare them when looking at their key differences and similarities. This is your comprehensive guide to the differences between amphibians and reptiles.
Defining Amphibians
Amphibians are cold-blooded tetrapod vertebrates. This means that animals classed as amphibians are generally four-limbed and possess a backbone. While estimates may vary slightly, it is believed that there are anywhere between 3000 and 8000 different amphibian species currently in existence. While the first amphibian appeared more than 300 million years ago, amphibians are the smallest group in terms of vertebrate species.
Every amphibian belongs to a higher species class known as Lissamphibia, comprised of tetrapods. The word ‘amphibian’ stems from the Greek phrase for living a double life, ‘amphibios’. The meaning of their name is no coincidence, either! The reason for their name stems from the diverse number of habitats that amphibians occupy.
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The habitats of different amphibians vary greatly. Some amphibian species are terrestrial and live only on land, while others may be fossorial and live almost exclusively underground. Many amphibians may live in arboreal habitats filled with different kinds of trees, while others could survive in freshwater bodies of water. A vast majority of amphibians live in tropical climates across the globe and are usually not too far from a source of fresh water. ‘Double life’ is thus a fitting meaning for the name of these versatile creatures!
Different Types of Amphibians
The reason that the habitats of amphibians are so varied is simply because the species is so diverse. In fact, amphibians themselves are divided into three distinct subclasses or orders. These subclasses are called:
- Order Anura
- Order Caudata
- Order Apoda.
Let’s take a look at each one…
Order Anura
This order includes frogs and toads, who themselves are then subclassified into roughly thirty different families. This order is also often referred to as ‘Salientia,’ which is comprised of all frogs and toads, as well as extinct frog species. Like the name for Amphibians is derived from the Greek word meaning ‘double life,’ the name ‘Anura’ stems from a Greek phrase that translates to ‘without tail.’
Order Caudata
This order includes species such as salamanders and newts, among others. The name Caudata harks back to the ancient Greek phrase meaning ‘tail.’ Salamanders may be visually reminiscent of lizards; however, they are not related to them at all. This coincidence is the result of an ancestral trait.
The Caudata order itself is divided into three different suborders. The first is Cryptobranchoidea, which refers to primitive salamanders. Of the first suborder, most of these species are found in fossils, and there are only three living species that remain. The second suborder, Salamandroidea, refers to more advanced salamanders that differ from the first suborder through superior physiology. The third subclass is the Sirenoidea, which contains various siren species, which are aquatic salamanders that are known to closely resemble eels.
Order Apoda
This order includes caecilians, which are limbless creatures that resemble the form of snakes or worms. This order is also referred to as ‘Gymnophiona,’ which stems from the Greek terms meaning ‘naked’ and ‘serpent.’ These amphibians are predominantly found in tropical parts of the world, such as South America. These creatures are more specifically found underground, often near damp soil or plant matter, though some can live in bodies of water.
Defining Reptiles
Like amphibians, reptiles are predominantly cold-blooded and are also tetrapod vertebrates. Unlike the name ‘amphibians,’ which derives from a Greek phrase, the word ‘reptile’ stems from a Latin phrase referring to ‘one who creeps,’ which is exactly what reptiles do. The different root languages for their names are also fitting, giving how similar and different Greek and Latin can seem – just like amphibians and reptiles.
Furthermore, the Latin meaning of ‘reptiles’ is especially fitting given that many reptiles have adapted to live on land over millions of years. However, before we begin comparing the similarities and differences between amphibians and reptiles, it’s important to know what a reptile is.
The class known as ‘Reptilia’ includes creatures such as lizards, snakes, crocodiles, and turtles, among others. Reptiles go back more than 300 million years to the Carboniferous period. ‘Carboniferous’ means to bear coal and refers to a period in time when a vast number of swamp forests produced much carbon.
Different Types of Reptile
Over these millions of years, many reptiles have adapted to live on land. Living reptiles are categorized into the following subgroups:
- Testudines
- Rhynchocephalia
- Squamata
- Crocodilia
Across these subgroups, there are more than 10,000 different species that are classified as reptiles. But let’s take a look at the different types mentioned above…
Testudines
The Testudines suborder refers to turtles and tortoises. In fact, the name is derived from the Latin word ‘testudo,’ which means tortoise. These famously slow-and-steady-paced creatures are identified by the shell that houses them, which is developed from their ribs and acts as protection. There are more than 300 living testudinal species, and these creatures are considered some of the most ancient reptiles in terms of their lineage.
Rhynchocephalia
The Rhynchocephalia suborder refers to only one living species and many extinct ones. The only living species in this suborder is the tuatara, which is native to New Zealand. The name means ‘beak head,’ which is a nod to its appearance. This suborder is the closest living relative to the following suborder that will be discussed, the Squamata suborder. Tuataras are considered more primitive than even the Testudines suborder.
Squamata
You guessed it; this suborder refers to snakes and lizards! The name of this suborder derives from the Latin word ‘squamatus,’ which literally means having scales or being scaly – but not in the scheming sense of the word. However, we would understand if snakes seem a bit scaly in both senses of the term. This suborder is the most diverse and is home to more than 7000 different species of snakes and lizards.
Crocodilia
As the name suggests, this suborder refers to a predatory species of reptiles called the crocodilians. The name stems from the Greek phrase ‘crocodilos,’ which translates to ‘lizard.’ Dating back 95 million years, there are currently 24 distinct species of crocodilians.
These themselves can be divided into three distinct groups. The first is Alligatoridae, which accounts for 8 of the 24 species, and includes caimans and, of course, alligators. The second subsect is Crocodylidae, which accounts for 14 different species of crocodiles. The last subsection is Gavialidae, which accounts for the remaining two species, namely Tomistoma and Gharial – or, as their friends call them, Tom and Gail.
These 24 distinct species are the closest surviving relatives of birds. Birds and crocodilians are the only survivors remaining of a group of reptiles known as the Archosauria.
The Key Differences Between Amphibians and Reptiles
Now that amphibians and reptiles have both been separately defined, it’s time to compare them. While they may seem similar in many regards, and you may even get confused as to which group certain creatures belong to, there are key differences between them.
Evolution
While both amphibians and reptiles date back more than 300 million years, which is technically the oldest? The first Amphibians date back an estimated 370 million years, while reptiles would only appear in another 55 million years. Reptiles are the youngest of the two species groups, only dating back an estimated 315 million years.
While both species groups are vertebrates, amphibians were the first land vertebrates. While it took millions of years, water-dwelling creatures eventually adapted to life on land. Amphibians had to evolve to breathe oxygen instead of getting it underwater. Fins also needed to evolve into legs in order for them to successfully navigate above-water terrain.
Species
While amphibians as a species are older than reptiles, there are an estimated additional thousand species of reptiles than there are amphibians. While reptiles were certainly not the first land vertebrates, they are the third biggest group of vertebrates, after fish and birds, respectively.
While there are more than 10,000 recognized species of reptiles around the world, there are an estimated 8000 different species of amphibians. However, when amphibian subspecies are taken into account, this number can often fluctuate.
Habitat
Amphibians have been around the longest when compared to reptiles. While a 55-million-year difference may seem ‘small’ when considering both of these 300-million-year-old species, it was enough time for the amphibians to adapt to survive in any number of environments. This is due to the way their respiratory systems have evolved over these millions of years.
From forests and farmland to rivers and lakes, you can probably find an amphibian friend near you without too much difficulty. With enough study of amphibians, you would be able to identify their natural habitat through certain characteristics, both physical and behavioral.
Reptiles, on the other hand, are far more simplistic creatures when it comes down to their natural habitat. Reptiles are land dwellers and, though you might find them near bodies of water, they prefer staying dry. Reptiles have evolved to only breathe air through their pulmonary systems and are thus perfectly adapted to life on land.
Skin
One of the reptile orders, Squamata, is named for a Latin phrase that translates to ‘having scales.’ This is an apt description. Reptiles are widely known for their scales, which often have peculiar yet beautiful patterns. Scales are not skin, however. A reptile’s skin is actually found beneath the scales. Their skin, when compared with mammal skin, is much thinner. Their skin, along with their scales, ensures that reptiles are watertight and that they can live on land, even in places where there is a dry climate.
The skin of amphibians, on the other hand, is often smooth and will feel wet to the touch. Due to the way they have evolved, their skin is very porous, and they possess multiple mucus glands. Amphibians also have a superpower of sorts. Through their glands, they can secrete toxic matter, which acts as a natural weapon again any possible predators. Reptiles, however, do not possess this ability.
Heart
When it comes down to the hearts of amphibians and reptiles, they are very similar in many regards. We’re not referring to the emotions of your amphibian or reptile pets here! Both species groups have three-chambered hearts, as well as two auricles. However, the rest is where they differ.
While amphibians only have one ventricle, reptiles have a ventricle that has a partial split. This allows reptiles to better process oxygenated blood and deoxygenated blood separately, ultimately increasing the efficiency of oxygenated blood flow in reptiles. Crocodiles also have a four-chambered heart, unlike other reptiles and amphibians. Overall, the ways in which their hearts work are very similar, with a few key divergences.
Respiration
Given that reptiles live on land, their respiratory systems are less complex than those of amphibians. Reptiles possess a pulmonary respiration system and, like humans, use lungs for breathing. While some amphibians do possess lungs, they have another way of breathing… through their skin!
Most amphibians breathe through both their skin and lungs, unlike reptiles. In order to absorb oxygen, they need to ensure that their skin stays moist. To aid this, they use their glands to secrete mucus that will help them remain wet (and alive). As oxygen enters through their porous skin, it immediately enters their blood vessels that circulate the air to the rest of their bodies.
There are, however, some outliers that do not breathe through the lungs and skin. Some amphibians simply do not possess lungs and therefore can only get oxygen through absorption via their skin. There are also aquatic amphibians, such as tadpoles, which have gills that they can use to breathe underwater.
Limbs
Amphibians typically have four limbs, except for the caecilians and certain salamanders who don’t have legs at all. Generally, amphibians have rather short front limbs and longer back limbs. Due to the wide variety of locales that they can inhabit, amphibians have webbed limbs that can support an aquatic lifestyle. Much like amphibians, reptiles typically have four limbs, though there are the occasional exceptions. Snakes, of course, do not have any limbs and slither on the ground.
Tongue
Reptiles are known for their characteristically split or forked tongues. Lizards, who are reptiles, actually use their tongue to smell. When lizards stick their tongues out, their tongues collect particles from the air, which, when placed on the roof of their mouth, allow lizards to smell things through sensory cells located there.
Amphibians, on the other hand, generally have even tongues that are quite muscular and do not fork. However, there are exceptions to this, with a few amphibians also having tongues that split in two, similarly to reptiles.
Eyes
When it comes down to eyesight, reptiles have amphibians beat. Unable to distinguish between many colors, amphibians are known to have a very narrow color range visible to them. Reptiles, on the other hand, are more advanced in terms of both their color sense and visual depth of field.
Some amphibians and reptiles have what is known as a ‘parietal’ eye, also commonly referred to as a third eye. Lizards, salamanders, and frogs are some different creatures that have this third eye. Also known as a pineal eye, this eye is photoreceptive and is linked with the pineal gland, which is why it is named so. This eye doesn’t usually stand out as it is typically covered with skin. This eye is sensitive to changes in light and is critical in regulating the body temperature of these creatures and their production of hormones.
Cranial Nerves
Cranial nerves are essential for motor and sensory functioning. These nerves allow different beings to experience various senses, such as taste, touch, smell, sight, and hearing. They essentially pass information from our exterior environment to our brains. Reptiles have a total of twelve pairs of cranial nerves, while amphibians only have ten.
Nitrogenous Waste
Metabolic waste is a matter that is leftover from various metabolic processes in living organisms. These substances cannot be used by the creature, so the body needs to find a way to excrete them. When nitrogen is eliminated from the body because it is in excess, it is known as nitrogenous waste.
For amphibians, ammonia is excreted as nitrogenous waste, while in reptiles, it is uric acid. These are two of four substances that are produced from the metabolism of protein. The other two are urea and creatinine.
Fertilization
The fertilization processes of amphibians and reptiles are complete opposites. While this process in reptiles is internal, for amphibians, the fertilization process is (most of the time) external. When the fertilization process is initiated amongst amphibians, there may be a specific mating call or scent involved. For reptiles, the males typically have one or two male reproductive organs they use to inseminate the female in order to reproduce. This leads us to our next topic…
Eggs
When reptiles reproduce, it always takes place on land. This is due to the way they have evolved and their inability to breathe through their skin the way amphibians do. The reptile reproduction process is always internal; however, births differ. While some reptiles lay eggs that have a hard-coated protective layer around them, others have live births.
Given that they’ve developed to breathe through their skin, amphibians lay their eggs in aquatic environments. These eggs are not hard like those of the reptiles, quite the opposite, in fact: they are coated with a soft gel-like substance. The babies that emerge from these eggs are known as tadpoles and larvae, and in this phase of their life use gills in order to breathe underwater. While in this stage of life, these tadpoles and larva will predominantly feed on algae and plants found in the water.
As they grow older, many will develop their legs, which will allow them to crawl on land, and their respiratory systems, which will allow them to also breathe on land. This gives rise to their very many possible habitats! The stage of life when amphibians are larva or tadpoles is unique to amphibians! Reptiles do not share this type of life stage. This is another key distinguishing factor that separates amphibians from reptiles.
Summary of Differences Between Amphibians & Reptiles
Here’s a handy table that summarizes the many differences between amphibians and reptiles (give or take a few exceptions, such as the odd animal being outside of the brackets explained in the table):
| Reptiles | Amphibians | |
|---|---|---|
| Species | More types reptile | Less types of amphibian |
| Habitat | Live on land | Live on land and water |
| Skin | Scales | Smooth & porous |
| Heart | Ventricle with partial split | One ventricle |
| Respiration | Breathe through lungs | Breathe through lungs & skin |
| Tongues | Split/forked tongues | Even muscular tongues |
| Eyes | Advanced color sense & visual depth of field | Narrow color range |
| Cranial Nerves | Twelve pairs | Ten pairs |
| Nitrogenous Waste | Nitric acid | Ammonia |
| Fertilization | Internal | External |
| Eggs | On land | In water |
Similarities Between Amphibians and Reptiles
While there are vast differences that distinguish reptiles from amphibians, they also share many similarities, like the fact that they are cold-blooded. In fact, there is a branch of science that is focused solely on both amphibians and reptiles known as Herpetology. This could be one reason why the two are so commonly confused! While birds are commonly grouped within Reptilia, they are not included here. Instead, the branch of science that studies birds is known as Ornithology.
To the untrained eye, it may be hard to tell the difference between amphibians and reptiles due to some shared traits. Both species groups are vertebrates and are cold-blooded, meaning that their body temperature and the maintenance thereof rely on their specific habitats. They also share similar eating habits, which the majority of amphibians and reptiles being omnivores that are able to sustain themselves on plant and animal matters.
There are some more unique traits that certain amphibian and reptile species share, such as the ability to change color the way a chameleon does. The chameleon is, of course, a reptile belonging to the lizard order discussed earlier. Some frogs, which are their own order of amphibians, share this ability too! Both species groups can use this trait to disguise themselves in the colors of dangerous or poisonous species as a defense mechanism in the wild. While they may be different in vast many different ways, when it comes to surviving in nature, some tactics just work!
Summary of Similarities Between Reptiles & Amphibians
Here’s a handy list of the similarities between reptiles and amphibians, and why it may be easy to sometimes get confused between the two species:
Amphibians and reptiles are both:
- Cold blooded
- Vertebrates
- Omnivores
- Many are also able to change color
Conclusion
While it’s easy to get them confused, the differences between amphibians and reptiles are plenty! Amphibians were around before the reptiles, dating back 370 million years. Reptiles would only arrive on the scene in another 55 million years. Their names, and the inspiration behind them, share this sentiment. The name ‘amphibians’ stems from the Greek phrase for ‘double life,’ which ‘reptiles’ stems from the Latin phrase for ‘one who creeps.’
While both groups are tetrapod vertebrates, amphibians are the smallest group of vertebrates. There are an estimated 8000 different amphibian species, while there are more than 10,000 species of reptiles currently living. Amphibians are classified into three distinct orders: Order Anura, Order Caudata, and Order Apoda. Reptiles are also split into different orders, though there are four: Testudines, Rhynchocephalia, Squamata, and Crocodilia.
While the habitats of different amphibians can vary greatly from bodies of water to land, amphibians were the first land vertebrates. Reptiles, as their name’s origin suggests, came later and are solely land dwellers who cannot live underwater. While reptiles have hard scales that cover their skin, amphibians can breathe through their skin due to their diversity in breathing on land and in water.
Their reproduction processes are also opposites, with amphibians reproducing externally and laying their eggs in water, which have a soft gel-like coating. Reptiles reproduce internally, however, either laying their eggs on land or giving live birth to their offspring. So, the life cycles of amphibians and reptiles continue.
While there are a few shared commonalities between amphibians and reptiles, leading to them both being studied under the branch of zoology known as Herpetology, there are even more differences between these species groups that set them apart from one another.
