Amphibians and Reptiles at the Cofrin Center for Biodiversity

Herps banner.

Amphibians and Reptiles: "Herps"

by Steve Price

Amphibians and reptiles share many characteristics. They both are ectotherms that rely on external heat sources to regulate internal body temperature. The first tetrapods were aquatic amphibians. They probably first used their legs to push along the bottom in ponds and streams. Some of these amphibians crawled out of their aquatic habitats and took up residence on land. Living amphibians and the reptiles evolved separately from 2 different extinct amphibian ancestors. The amphibians are divided into 3 subclasses: the extinct Lepospondyli; the extinct Labyrinthodontia, which are ancestral to the reptiles, mammals and birds; and the Lissamphibia or modern amphibians.

Possibly the most important difference between the amphibians and reptiles is water. Amphibians are tied to water for respiration and reproduction. Even salamanders and toads that have lungs gain as much as 35% of their oxygen by absorbing it through their skin (Withers, 1992). Reptiles were able to leave water completely only after evolving a relatively water-proof skin and an amniotic egg. A hard shell and membranes around the developing embryo limit water loss. Because of this reptiles are in some ways closely allied with birds and mammals.

The most characteristic shared trait between modern day amphibians and reptiles is ectothermy. Ectothermic animals are "cold-blooded" and must rely on an outside source of heat to regulate body temperature and activity levels. In order to remain physiologically active for long periods of time, animals must maintain a high core body temperatures. Ectotherms usually keep warm by muscle activity or by sunning.

The reason these 2 groups are studied together is mainly historical. As recently as 100 years ago amphibians were classified as a sub-group of reptiles and studied together as the field of herpetology. This historical classification has been preserved and herpetologists still study both amphibians and reptiles, but many specialize on one or the other. In fact herpetologists often refer to amphibians and reptiles singly as "herps" or sometimes even "herptiles".

Biodiversity Topics: Introduction . Plants . Animals . Mammals . Birds . Reptiles & Amphibians . Arthropods . Spiders . Insects