Nota de aplicación
Class of vertebrate animals characterized by their ability to exploit both aquatic and terrestrial habitats, typically animals that lay eggs in water, in their early state breathe by gills like fishes, breathe air as adults but have moist skin and rely heavily on cutaneous (skin-surface) respiration, possess a double-channeled hearing system, have green rods in their retinas to discriminate hues, and pedicellate (two-part) teeth. They are represented by nearly 6,200 extant species; their ancestors emerged around 340 million years ago during the Upper Mississippian Epoch in the evolution of animals from strictly aquatic forms to terrestrial types. Modern examples are frogs and toads, newts and salamanders, and caecilians.
- Moliner, María, "Diccionario de uso del Español", vol. 2, Gredos S.A., España, Madrid, 2004, p. I:179
- S/A, "La Enciclo", vol. 3 Volúmenes, Arrayán, 1993, p. 64