Comparison of Reptiles & Amphibians

Reptiles are often grouped with amphibians but are very different.

Herpetology, the study of amphibians and reptiles, gets its name from the Greek word "herpeton," which means "crawling." Historically, these two groups have been grouped together under one branch of zoology (the study of animals). However, modern amphibians and reptiles form two very distinct lineages with equally different characteristics.

Skin

Amphibian skin is smooth, moist and permeable.

Amphibians possess relatively smooth (without scales) skins, whereas reptiles have skin covered with scales that are often modified into protective spikes. Reptile skin is essentially waterproof; amphibian skin forms a semi-permeable membrane that allows water (and dissolved minerals or chemicals) and oxygen to be absorbed through the skin. However, amphibian skin boasts a high density of glands that secrete waxy substances that help to waterproof the skin.

Respiration

Some salamanders have evolved to live without lungs.

Reptiles respire (exchange oxygen and carbon dioxide with the environment) with a well-developed pair of lungs. In sharp contrast, some amphibians lack lungs altogether. Amphibians are able to exchange gases across the permeable skin of their bodies (including their mouths). An extensive network of small capillaries in the skin increases the efficiency of gas exchange.

Egg Structure

Like chicken eggs, reptile eggs form a self-contained environment for the embryo.

Amphibian eggs, with few exceptions, require moisture to survive and develop. Amphibian eggs are coated with a hydrophilic (water-loving) protein coat that rapidly absorbs moisture from the environment after they are laid and helps to protect the eggs from drying. Some amphibian eggs are laid in the water, while others are laid on soil or plants or in much more unusual locations. Some frogs swallow their eggs and hatch them in their stomachs. Reptile eggs are protected by leathery shells, with layers of membranes inside that prevent the eggs from drying.

Egg Fertilization

Most amphibians and reptiles fertilize eggs using very different methods.

As amphibian and reptile eggs pass through the female reproductive tract, they are given a coating. Male amphibians of most species fertilize the female's eggs externally, after they are laid. The sperm penetrate the protein jelly coat before it absorbs water and thickens. Male reptiles of all species must fertilize the female's eggs internally, before the impenetrable leathery shell is added to the egg.

Life Cycle

Amphibians complete an aquatic larval stage, then metamorphose into adult form.

Most amphibians have a complex life cycle that includes an aquatic larval stage and a somewhat terrestrial adult stage. The name "amphibian" describes this complexity--"amphi" means "both" and "bios" means "life." In comparison, female reptiles give birth to live young or lay eggs that hatch into young that are small replicas of the adult.

References

• University of Georgia Savannah River Ecology Laboratory: Reptile and Amphibian Traits
• Stonehill College Field Guide: Reptiles & Amphibians

Resources

• CNAH: The Center for North American Herpetology