#Evolve stage 2 skins skin#
The skin is also one of three respiratory surfaces used by amphibians. Most water is taken in across the skin rather than by drinking. An important characteristic of extant amphibians is a moist, permeable skin that is achieved via mucus glands. In some species of salamanders, hindlimbs are reduced or absent, but all caecilians are (secondarily) limbless. They have not changed much in morphology over the past 350 million years!Īs tetrapods, most amphibians are characterized by four well-developed limbs. 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 represent an evolutionary transition from water to land that occurred over many millions of years. Amphibians evolved during the Devonian period and were the earliest terrestrial tetrapods. In fact, they cannot stray far from water because their reproduction is intimately tied to aqueous environments. 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. Describe the evolutionary history of amphibiansĪmphibians are vertebrate tetrapods (“four limbs”), and include frogs, salamanders, and caecilians.Distinguish between the characteristics of Urodela, Anura, and Apoda.Describe the important difference between the life cycle of amphibians and the life cycles of other vertebrates.By the end of this section, you will be able to do the following:
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