Reptiles and amphibians are often grouped together, sometimes under the term “herpetofauna,” but they are distinct biological Classes (Reptilia and Amphibia). They separated evolutionarily millions of years ago. Both groups are vertebrates and rely on external heat sources to regulate body temperature. However, their fundamental biology, especially skin structure and reproductive strategies, is profoundly different. Understanding their classification clarifies how each group adapted to life on land, with reptiles achieving independence from water and amphibians maintaining a vital link to aquatic environments.
Defining Characteristics of Reptiles
The defining traits of reptiles (snakes, lizards, turtles, and crocodiles) are adaptations for life on dry land. Their skin is covered in dry, hard, keratinous scales or scutes that minimize water loss and act as a protective barrier against desiccation. Reptiles reproduce using internal fertilization.
They develop the amniotic egg, a shelled egg containing membranes that provide the embryo with a self-contained, watery environment. The shell is often leathery or calcified, preventing water loss and freeing them from needing to lay eggs in water. All reptiles breathe using lungs throughout their life cycle, hatching as miniature versions of the adult form.
Defining Characteristics of Amphibians
Amphibians (frogs, toads, salamanders, and newts) are defined by a “dual life,” reflected in their name meaning “both kinds of life.” Their skin is thin, soft, and highly permeable. This porous skin allows for cutaneous respiration, meaning they absorb oxygen directly through the skin. However, it also makes them sensitive to toxins and requires them to stay near moist habitats to prevent drying out.
The life cycle involves metamorphosis. They begin life as aquatic larvae, like tadpoles, possessing gills for underwater breathing. Larvae then develop lungs and limbs to transition into a terrestrial or semi-terrestrial adult form. Reproduction relies on external fertilization, where the female lays non-shelled, jelly-like eggs in the water for the male to fertilize.
Why the Two Groups Are Often Confused
Confusion between reptiles and amphibians stems from functional similarities and superficial resemblances. Both groups are ectotherms, meaning they rely on external sources like sunlight to regulate their body temperature. This shared need to bask or seek shade means they are often found in similar habitats.
Certain species also exhibit similar body plans. For example, some amphibians, like salamanders and newts, possess an elongated body shape that can be mistaken for a reptile, such as a lizard. Historically, scientists grouped these animals together under the study of “herpetology” simply because they were neither birds nor mammals, perpetuating the idea that they are closely related.