Section 1

Origin and Evolution of Amphibians

• Preadaptations are inherited traits used for new functions for which the traits are later selected.

• Fleshy fins with strong bone structure, nostrils, and lungs were preadaptations that allowed the transition from aquatic to terrestrial life.

• Early amphibians had lungs and four legs. Like lobe-finned fish, they were predominantly aquatic, they had a lateral line and a fishlike tail fin, similar skull and vertebral column, similar limb bones, and some had gills.

Vocabulary preadaptation (p. 799)

• Modern amphibians share several characteristics. Most change from aquatic larvae to terrestrial adult. Most have moist thin skin, with no scales. Feet, if present, lack claws and are often webbed. Most use gills, lungs, and skin in respiration. Most lay eggs that lack multicellular membranes or shells.

• Modern amphibians are divided into three orders: Anura (frogs and toads), Caudata (salamanders), and Gymnophiona (caecilians).

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