Amphibians and reptiles differ in their skin, reproduction, development and dependence on water. Amphibians generally possess a moist, glandular and permeable skin. It can also take part in respiration. The skin of reptiles is comparatively dry and keratinized, with scales. They depend on lungs for breathing.
In most amphibians, the eggs are without a shell and are laid in water or moist places. A larval stage is common. In many frogs and salamanders, this is followed by metamorphosis.
Reptiles are amniotes. Fertilization occurs internally, and the embryo develops within amniotic membranes. In egg-laying reptiles, the egg has a leathery or calcareous shell. Their young normally resemble the adult, without an aquatic larval stage. Both groups are ectothermic vertebrates. Reptiles are much less dependent on water during reproduction and development.
Amphibians vs Reptiles – Comparison Table
| Feature | Amphibians | Reptiles (non-avian) |
|---|---|---|
| Skin | Skin is generally moist, glandular and permeable. | Comparatively dry skin with a keratinized covering. Scales or scutes are usually present. |
| Habitat | Members live in water or moist places on land. Some remain aquatic throughout life. | Terrestrial and aquatic forms are both present. Many members also live in dry habitats. |
| Dependence on water | Most require water or moist surroundings for reproduction and development. | Reproduction is less dependent on external water. |
| Fertilization | Usually external in frogs and toads. In most salamanders and all caecilians, fertilization is internal. | Internal fertilization occurs. |
| Egg covering | Eggs lack a leathery or calcareous shell. A jelly covering is generally present. | In egg-laying members, eggs possess a leathery or calcareous shell. |
| Amnion | Absent. | The embryo is enclosed within an amnion, a membrane surrounding a fluid-filled cavity. |
| Development | A larval stage followed by metamorphosis is common. Some members develop directly, without a free-living larva. | Development is direct. Young resemble the adult, and an aquatic larval stage is absent. |
| Respiration | Gills are common in aquatic larvae. Many adults use lungs, skin and the lining of the mouth for gas exchange. Lungs are absent in certain members. | Lungs are the main respiratory organs, including in aquatic forms. |
| Limbs | Most adults possess two pairs of limbs. Caecilians are limbless, and some salamanders have reduced limbs. | Four limbs are present in many members. In snakes and certain lizards, limbs are absent or greatly reduced. |
| Heart | Adults possess two atria and one ventricle. | Most have two atria and a partly divided ventricle. Crocodiles and alligators possess a four-chambered heart. |
| Mode of birth | Egg-laying forms are common. Some salamanders and caecilians give birth to live young. | Members may lay eggs or give birth to live young, depending on the species. |
| Examples | Frogs, toads, salamanders, newts and caecilians. | Lizards, snakes, turtles, tortoises, crocodiles, alligators and tuatara. |
Differences Between Amphibians and Reptiles
- Skin – Amphibians have a thin, moist and glandular skin. Scales are absent in most living amphibians. Reptiles possess a comparatively dry skin, covered with keratinized scales or scutes which reduce loss of water from the body.
- Dependence on water – Amphibians remain closely associated with water or moist surroundings, particularly for reproduction and development. Reptiles are less dependent on water and many of them can complete their entire life cycle on land.
- Eggs – The eggs of amphibians are non-amniotic and without a shell. Usually they are surrounded by gelatinous coverings and deposited in water or a moist place. In egg-laying reptiles, amniotic eggs are formed, surrounded by a leathery or calcareous shell.
- Fertilization – External fertilization is common in amphibians, particularly among frogs and toads. But this is not true for all; internal fertilization occurs in many salamanders and caecilians. In reptiles the fertilization is internal.
- Development – A larval stage occurs in the life cycle of most amphibians. The larva undergoes metamorphosis and changes into the adult form, although direct development occurs in some species. Reptiles generally show direct development; the young comes out as a smaller form of the adult and there is no aquatic larval stage.
- Respiration – Amphibian larvae commonly respire by gills. In adults, lungs and the moist skin may both take part in respiration; some amphibians depend greatly on cutaneous respiration. Reptiles breathe through lungs, and their keratinized skin is not used as an important respiratory surface.
- Skin glands – Mucous glands are well developed in amphibian skin and keep its surface moist. Poison glands are also found in many amphibians. The reptilian skin contains comparatively few glands.
- Body covering and shedding – In amphibians the outer skin is soft and is periodically shed. Reptiles also shed the epidermal covering, but it is strongly keratinized; snakes commonly cast it in large pieces or almost as one continuous layer.
- Limbs and claws – Where limbs are present, amphibians generally lack true claws. Reptilian digits usually bear claws. Limbs, however, have become reduced or completely lost in snakes and in some lizards.
- Heart – Adult amphibians normally possess a three-chambered heart, with two atria and one ventricle. Most reptiles also have two atria, but the ventricle is partly divided. Crocodilians differ from the other living reptiles in having a four-chambered heart.
- Nitrogenous waste – Aquatic amphibian larvae commonly excrete ammonia, while terrestrial adults mainly eliminate urea. Uric acid is the principal nitrogenous waste in most reptiles, which helps to conserve water.
- Embryonic membranes – Amphibian embryos do not develop the amnion characteristic of amniotes. Reptilian embryos possess extra-embryonic membranes, including the amnion, chorion and allantois, which permit development with much less dependence on an external body of water.
- Young ones – Tadpoles or other aquatic larvae may differ greatly from the adult amphibian in body form, feeding and respiration. Young reptiles already have the basic body organization of adults.
- Examples – Frogs, toads, salamanders, newts and caecilians are amphibians. Turtles, crocodilians, snakes and lizards are reptiles.
Similarities Between Amphibians and Reptiles
- Vertebrates- These are members of Vertebrata. An internal skeleton with a skull and vertebral column is present in both amphibians and reptiles.
- Tetrapods- Two pairs of limbs are present in the basic body plan, but in certain members these are reduced or absent. Snakes and caecilians descended from four-limbed ancestors. They are also placed under tetrapods.
- Body temperature- Most body heat is obtained from the surroundings. Amphibians and living non-avian reptiles are generally ectothermic, commonly referred to as “cold-blooded” animals. Their body is not always cold.
- Lungs- Reptiles and many adult amphibians use lungs for respiration. In some amphibians, particularly the lungless salamanders, lungs are absent.
- Blood circulation- Both possess a closed circulatory system in which blood is pumped through blood vessels by the heart.
- Heart- Two atria and one ventricle are present in adult amphibians and most non-avian reptiles. In most reptiles, the ventricle is partly divided. Crocodiles and alligators are exceptions, having a four-chambered heart.
- Reproduction- Members usually reproduce sexually. Many amphibians and reptiles lay eggs, while live-bearing forms are also found in both groups.
Examples of Amphibians and Reptiles
Examples of Amphibians
- Frogs- These are members of Anura. Tail is absent in adults, and the long hind limbs are used for jumping and swimming. Their aquatic larva is referred to as a “tadpole”.
- Toads- Most toads possess a stout body with comparatively rough, warty skin. They are also placed under Anura.
- Salamanders and newts- Aquatic and terrestrial forms are both present. In most salamanders, four limbs are present and the tail is retained in adult stage. Newts are a type of salamander.
- Caecilians- These are limbless amphibians with an elongated, worm-like body. Most members burrow in soil. The body shape helps them to move through it.
Examples of Reptiles
- Lizards- Some of the examples are geckos, chameleons and monitor lizards. Two pairs of limbs are present in most members, but in certain lizards these are reduced or absent.
- Snakes- The body is elongated and covered with scales. Movable eyelids are absent. Pythons and garter snakes are examples of this group.
- Turtles and tortoises- Members are placed under Testudines. Their shell consists of an upper part (carapace) and a lower part (plastron). Tortoises live on land.
- Crocodiles and alligators- These are large, semiaquatic members of Crocodilia.
- Tuatara- It is found naturally in New Zealand and has a lizard-like appearance. Tuatara is classified under a separate group called Sphenodontia.
References
- Clark, M. A., Douglas, M., & Choi, J. (2018). Biology (2nd ed.). OpenStax. https://openstax.org/details/books/biology-2e
- Fowler, S., Roush, R., & Wise, J. (2013). Concepts of biology. OpenStax. https://openstax.org/details/books/concepts-biology
- Lowie, A., De Kegel, B., Wilkinson, M., Measey, J., O’Reilly, J. C., Kley, N. J., Gaucher, P., Brecko, J., Kleinteich, T., Adriaens, D., & Herrel, A. (2022). Is vertebral shape variability in caecilians (Amphibia: Gymnophiona) constrained by forces experienced during burrowing? Journal of Experimental Biology, 225(12), Article jeb244288. https://doi.org/10.1242/jeb.244288