Many features that evolved from early tetrapods are related to the key transformations from water to land, and are inherited by their descendants – the amphibians. For this reason, amphibians have a real tongue (to moisten and to move food), eyelids (connected to glands nearby to moisten the cornea), an outer layer of dead cells on the skin that can be shed, first pair of real ears (and a sound producing structure – larynx), and the first vomeronasal organ – a chemoreceptor structure which is connected to the nasal cavity; the evolution continue to climax in lizards and snakes. It is hypothesized that the same features may be found in tetrapods – the ancestors of amphibians that are extinct.

The nervous system has significantly altered to adapt a more intricate terrestrial environment; the spinal cord has extended to the regions that closer to the appendages. This is associated with the movement of appendages that is more complex than the fins of the ancestors of fish. Nervous cells entering the outer layer of the cerebral hemisphere are found on amphibians but are not as extensive as to that of mammalian brains.

The skins of present day amphibians maintains moisture through secretions from many mucus glands, however, this is not the just a passive exterior layer, but one that plays an active role in maintaining life through water equilibrium, respiration, and protection. The skin of some frogs has antibiotic substances (magainin). The skin has great water permeability, especially for terrestrial species. The aquatic species counteract with the inflow of water through osmosis to reduce permeation.

Although most amphibians are restricted to humid environments, functional specializations allow many species to dwell in inhabitable settings; for example, by retaining urea in the urine, the desert toads generated osmotic gradients in the skin so that water may be absorbed from extremely dry soil. Most terrestrial frogs have skin patches that are densely vasculated around the pelvic area; it is a thin membrane but can absorb water effectively. Other frog and a number of salamander species may form a protective layer that is sheddable to prevent loss of water; certain species of tree frogs reduce water loss due to evapotranspiration by coating a fat-like skin secretion on the surface of the body.

On the other hand, water loss through the skin is being implemented as a way to regulate body temperature through evaporative cooling. The moist skin in the oral cavity and the exterior surfaces may provide the respiratory function to most species as dissolved gas may be completely permeated. Many species from one family in salamander (family Plethodontidae) are without lungs, and conduct gas exchange through this model.