Last Updated on July 17, 2020 by Sagar Aryal
Amphibians are a group of cold-blooded vertebrates that are capable of exploiting both aquatic and terrestrial habitats.
- The term ‘amphibian’ is derived from the Greek word ‘amphibios’ which means living a double life.
- The term thus reflects the dual life of these animals even though some species in this group might be permanent land dwellers while others might live permanent aquatic life.
- About 8100 species of living amphibians dwell throughout the world with the first organism that appeared approximately 370 million years ago.
- Modern amphibians are divided into three orders, each of which contains different categories of animals.
- Order Anura includes toads and frogs; Order Caudata includes salamanders and newts and Order Apoda includes caecilians.
- The three orders are separated on the basis of their different appearances or structures.
- Frogs lack tail but have two pairs of limbs with longer and powerful hindlimbs. Salamanders have tails and two pairs of limbs of about the same size. The caecilians, however, are limbless and are adapted for burrowing existence.
- Many amphibians might share some unique characteristics.
- Most of the amphibians have moist skin and thus rely heavily on cutaneous respiration. Some terrestrial salamanders and frogs might even lack lungs.
- Usually, the larval forms of these animals might possess gills that allow the young ones to survive in the water. The gills disappear during the metamorphosis of the larva into adult forms.
- These animals possess a double hearing system and have green rods in their retina to discriminate between different colors.
- Amphibians reproduce sexually either through internal or external fertilization. They have specific scents or mating calls to attract their mating partners.
- Because amphibians do not produce amniotic eggs, most of them are obligate breeders in water. The adult lays eggs in water, and the developing larva survives in water, looking for food and escaping predators at the same time.
- In the case of internal fertilization, however, the young ones develop within the oviduct of the female, feeding on the walls of the ducts.
- Amphibians are one of the most susceptible animals in the environment because of their porous eggs and semipermeable skin.
Reptiles are cold-blooded vertebrates that live on land and have epidermal scales, covering part or the entire surface of the body.
- The characteristics of animals within reptiles might differ with some reptiles being closer to amphibian while others are closer to birds.
- Most reptiles are tetrapods with two pairs of limbs, and they are exclusively terrestrial and do not have an aquatic larval stage.
- More than 10000 species of reptiles are known to live on earth with the first reptiles observed about 312 million years ago.
- Modern reptiles are divided into four orders based on their physical appearance.
- Order Squamata includes lizards and snakes; order Crocodilia includes crocodiles and alligators, order Testudines includes turtles and tortoise, and order Sphenodonta includes tuarata.
- The extinct reptiles are even more diverse, ranging from aquatic plesiosaurs to meat-eating terrestrial dinosaurs.
- Most reptiles have an epidermal covering on their skin which is composed of beta-keratin. The shape and size of these scales defer depending on the species.
- These are air-breathing animals and thus have a developed pulmonary system. Some of the reptiles have a pair of limbs while others are limbless.
- All reptiles shed the outer layer of their skin regularly. Because they are cold-blooded animals, their metabolism changes with the temperature of the surrounding.
- Most of them reproduce sexually, and sexual reproduction is internal where the sperm is deposited by copulation. Asexual production by parthenogenesis is observed in some groups.
- Only boas and python live birth to young ones while the rest of them lay eggs in a simple nest. The eggs are amniotic and covered with calcareous shells.
- Hatching occurs within days or a month during which the temperature of the soil is critical. The temperature of the soil determines the sex of the young ones.
- Most reptiles are diurnal animals and also have a better, more advanced color sense and visual depth.
Key Differences (Amphibians vs Reptiles)
Basis for Comparison
|Definition||Amphibian is a group of cold-blooded vertebrates that are capable of exploiting both aquatic and terrestrial habitats.||Reptiles are cold-blooded vertebrates that live on land and have epidermal scales, covering part or the entire surface of the body.|
|Distinct feature||Amphibians are animals with a dual-mode of existence.||Reptiles are creeping or crawling animals.|
|Skin||The skin of amphibian is smooth, moist, highly porous, and sometimes sticky with numerous mucus glands.||The skin is covered by dry scales arranged in a particular pattern. The actual skin is found underneath the dry scales, which are made of keratin.|
|Amphibian skin is provided with glands that produce toxic secretions which act as a defense mechanism against its predators.||No such glands are found on the skin of reptiles.|
|Respiration||Most adult amphibians respire through their skin while some also have lungs. A young tadpole living in water respires via gills.|
|The primary mode of respiration in reptiles is pulmonary respiration, and they cannot respire through the skin.|
|Limbs||They have short forelimbs and long hindlimbs with five webbed digits.||They usually have four limbs except for snakes that don’t have any limbs and thus, crawl on land.|
|Heart||The heart in the case of amphibians is a three-chambered with two auricles and a ventricle.||The reptilian heart is three chambered with two auricles and a falsely divided ventricle. Crocodiles are the only reptiles with a four-chambered heart.|
|Eyes||Amphibians have a narrow color range and cannot discriminate between many colors.||Reptiles have a better, more advanced color sense and visual depth.|
|Tongue||The amphibian tongue is mostly entire even though some might have a tongue bifurcated at the tip.||The bifurcated tongue is a characteristic feature of reptiles.|
|Cranial nerves||Amphibians have 10 pairs of cranial nerves.||Reptiles have 12 pairs of cranial nerves.|
|Evolution||First amphibians were seen about 370 million years ago.||First reptiles were seen about 315 million years ago.|
|Species||About 5500 species of amphibians are identified worldwide.||About 6500 species of reptiles are identified worldwide.|
|Nitrogenous waste||The primary nitrogenous waste in amphibians is ammonia.||Uric acid is the primary nitrogenous waste in reptiles.|
|Fertilization||Fertilization in amphibians is external.||Fertilization in reptiles is internal.|
|Eggs||Amphibians lay their eggs in water which are covered with gel.||Reptiles lay their eggs on land and are covered with a hard calcareous and leathery protective covering.|
|Larva||The life cycle of amphibians contains an aquatic larval form.||No aquatic larval form is present in the reptilian life cycle.|
Examples of Amphibians
- Frog is a tailless amphibian belonging in the order Anura of Phylum Amphibia.
- Most of them are aquatic while some live both land and on water, and some are entirely terrestrial.
- An adult frog has a stout body with protruding eyes and two pairs of limbs. The forelimbs are shorter and weak while the hind legs are long and powerful.
- The body of the frog, like other amphibians, is covered with moist skin that performs the primary function of respiration. Some frogs are known not even to have lungs.
- The skin of some frogs has multiple glands that secrete harmful secretions as a defense mechanism.
- Frogs have a distinct long tongue that is almost one-third of the total length of the body.
- The tongue is also sticky, which enables them to catch their prey. Adult frogs are mostly carnivorous, and they feed on tiny insects.
- The breeding of frogs occurs during the rainy season and occurs in freshwater. Frogs attract their mates by mating calls or mating secretions.
- The fertilization can be either internal or external, but they always reproduce by laying eggs. The eggs hatch in the water, and thus the tadpole lives an aquatic life.
- A salamander is a group of amphibians that has a lizard-like appearance with a stout elongated body, two pairs of short limbs, and a tail. Some might even have an eel-like appearance.
- Salamanders like frogs are also diverse. Most of them live in water their whole life while others move to the water intermittently, and some are entirely terrestrial.
- The skin of salamander is thin, permeable to water, and has numerous glands to keep it moist. The skin has cornified layers which are periodically shed.
- The skin has different cryptic colors which allow them the mechanism of camouflage.
- Most salamanders are predators, and they feed on crabs, fishes, and small mammals. Both adult and young salamanders have teeth on both upper and lower jaws.
- Fertilization is internal in about 90% of them where the male spreads the sperm on the ground, which is then picked up by the female.
- The tadpoles hatch out of the eggs in about a few weeks, and the tadpole spends most of its time in the water. It then undergoes metamorphosis to form adult salamander.
Examples of Reptiles
- Crocodiles are mostly aquatic reptiles that are about 2 m in size and weigh about 1000 kgs.
- They have a streamlined body covered with keratinized scales. This helps the animals survive in the water.
- These are known to have large teeth, two pairs of short limbs, and clawed webbed feet and a massive tail.
- The unique structure of the body allows the crocodile to remain inside the water even though the eyes, nose, and ears remain outside.
- These are cold-blooded animals, and that is why they alternate between swimming in the sun and shade to maintain their body temperature. During cold, the dig vast burrows to keep their body warm.
- Fertilization is internal and mostly takes place in the water. The eggs, however, are laid on land and are mostly deposited in holes.
- The young ones take about 2-3 months to develop before hatching fully. The female provides protection to the young ones for several weeks to months.
- Turtles are reptiles with a body enclosed in a bony shell consisting of a carapace on top and plastron on the bottom.
- The shell is an essential organ of a turtle that is made up of bones and cartilages. The shell remains throughout the life of the turtle and is not shed like other reptiles.
- Turtles can live either on land or in water depending on the species.
- Turtles have hard beaks on their head along with jaws that help them chew and cut food.
- They have two pairs of limbs with webbed feet. They are known for moving very slowly. Some sea turtles might have flippers instead of legs.
- Fertilization is internal, and they lay eggs on lands. Unlike crocodiles, turtles do not show any parental care after birth.
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