Amphibians are vertebrate tetrapods (“four limbs”), and include frogs, salamanders, and caecilians. The term “amphibian” loosely translates from the Greek as “dual life,” which is a reference to the metamorphosis that many frogs and salamanders undergo and the unique mix of aquatic and terrestrial phases that are required in their life cycle. In fact, they cannot stray far from water because their reproduction is intimately tied to aqueous environments. Amphibians evolved during the Devonian period and were the earliest terrestrial tetrapods. They represent an evolutionary transition from water to land that occurred over many millions of years. Thus, the Amphibia are the only living true vertebrates that have made a transition from water to land in both their ontogeny (life development) and phylogeny (evolution). They have not changed much in morphology over the past 350 million years!

Link to Learning

Watch this series of five Animal Planet videos on tetrapod evolution:

  • 1: The evolution from fish to earliest tetrapod
  • 2: Fish to Earliest Tetrapod
  • 3: The discovery of coelacanth and Acanthostega fossils
  • 4: The number of fingers on “legs”
  • 5: Reconstructing the environment of early tetrapods