17.3 AmphibiansPage 353

Movement Onto LandAmphibians evolved from lobe-finned fish,

now extinctAs they evolved, fins got stronger & more

supportiveUsed for swimming & crawling

Fossil records suggest these fins evolved into two pairs of legs

Amphibian Examples

Amphibian CharacteristicsGills & simple lungs evolved into lungs able

to exchange gases with atmosphereBegan using skin for respirationAlthough adapted to land life, still need water

Reproduction

Amphibian ReproductionDepend on water

Eggs don’t have waterproof shellEggs laid in water and externally fertilized by

maleMany amphibians develop into a fish-like

larval stage (tadpole)

Red-Eyed Tree Frogs

Red-Footed Tortoise

Frogs & ToadsNo tailsSpend lives in & around water

Frog ReproductionHundreds of eggs laidMale fertilizes outside bodyEggs hatch tadpoles in several weeksMost toads similarSome species – no tadpoles

TadpolesThey have gills, fins, tails, streamlined bodyUndergoes great changes

(METAMORPHOSIS)Once complete, adult is land-dwelling

vertebrate

Salamanders & NewtsAmphibians with tailsSmooth, moist skinSome live in dry habitats, some moist, some

water