The Difference Between Amphibians and Reptiles

We share our urban backyards and ravines, rural streams, ponds and countryside with hundreds of species of amphibians and reptiles. While they have characteristics in common — both are cold-blooded vertebrates and all but crocodiles have three-chambered hearts – there are several clear distinctions between amphibious and reptilian species. From their reproduction and development to their physical appearance and the role that water plays in their lives, amphibians and reptiles are markedly different animals.

Reproduction and Dependence on Water

Amphibians are the most primitive class of terrestrial vertebrates, the first group of vertebrates to emerge from an aquatic environment to live on land for most of their adult lives. Reptiles were the first vertebrates to become completely adapted to a terrestrial life, and unlike amphibians, did not originate in water. Most amphibians externally fertilize their eggs, which are soft. The young begin life in the water as larvae that breathe through gills, gradually changing through the process of metamorphosis into adults that breathe using lungs or through their skin. Few amphibious adults are entirely independent of water, requiring water sources to breed.

Reptiles are primarily oviparous and lay leathery, hard-shelled eggs, but some are viviparous, or bear live young. Most are internally fertilized similar to mammal reproduction. All young are miniature versions of the adults and breathe through lungs; there is no aquatic larval stage.

Skin and Physical Appearance

Most amphibians don’t have scales, and their moist, sticky skin is used in respiration. They need to live in a damp environment, otherwise body fluids easily seep through their thin skin. Most reptiles have thick, scaly skin that is either smooth or rough, and it prevents them from drying out — it is also dry to the touch, not slimy like an amphibian. Reptiles with extreme scales, turtles and tortoises, have undergone few changes in over 200 million years; their hard outer shell is composed of bony plates covered by horny scales.

Size-wise, with the exception of three species of giant salamanders that grow to almost 6 feet, amphibians are typically smaller than reptiles. Gargantuan reptilian species are the 12-foot-long Komodo dragon — the largest living lizard — the 15-foot crocodile and the 25-foot anaconda snake who lives in the swamps and slow-moving rivers of the Amazon forests.

Species Diversity in Amphibians

Amphibious species comprise three living orders in 20 different families, with thousands of species of frogs, toads, newts and salamanders throughout the world. One unusual and little-known legless species of amphibians called caecilians resemble earth worms and live in South America, tropical Africa and southeastern Asia.

Species Diversity in Reptiles

Reptilian species are found throughout the world and comprise four orders and four suborders in 42 different families, with more than 4,800 species of turtles, tortoises, lizards, snakes, alligators, crocodiles and the relatively unknown and rather bizarre amphisbaenians, or worm-lizards. One species, tuatara, is the sole survivor of its family Sphenodon; the others became extinct more than 100 million years ago. Reptilian species are more physically diverse than amphibious species; many species have limbs, turtles and tortoises carry a hard shell on their backs and the sub-order Serpentes is composed of hundreds of species of snakes, all legless, in 11 families, many of which are dramatically different; some are quite harmless, while others are deadly.