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Amphibians CH. 30.3 Amphibians are the only modern descendants of the ancient group that gave rise to all other land vertebrates What is an Amphibian? ‘Double life’ Larva are fishlike that use gills Adults are terrestrial that use lungs Vertebrate that lives in water as larva, land as adults, breath with lungs, has moist skin, contains mucus glands, and lacks scales and claws Evolution of Amphibians First amphibians resembled lobe fined fish; however, they had legs ~ 360 mya Transition from water to land also meant protecting themselves and their eggs from drying out, support themselves from the pull of gravity Early amphibians evolved adaptations: Limbs and limb girdles became stronger Lungs and breathing tubes enabled to breathe air Breastbone formed a bony shield to support and protect internal organs Underwent major adaptive radiation Became the dominant form of life in the swampy forest 360-286 mya Most amphibian groups became extinct 245 mya 3 orders survived: frogs and toads, salamanders, and caecilians Form and Function in Amphibians Feeding: tadpoles are filter feeders or herbivores that graze; adults are almost entirely carnivorous Intestines always filled with food CLOACA is where digested wastes leave the body Respiration: gas exchange through the skin and gills in the larva; lungs take place of gills after adulthood Circulation: circulatory system is a double loop 1st loop: carries oxygen poor blood from heart to lungs and skin; oxygen rich blood from lungs and skin back to the heart 2nd loop: carries oxygen rich blood from heart to rest of body and oxygen poor blood from body back to the heart Excretion: kidneys filter wastes from the blood Reproduction: female lays eggs in water and males fertilize externally Abandon eggs after laying them Movement: use front and back limbs to move. Use s- shaped curves to push backwards against the ground; some jump with well developed hind legs Response: well developed nervous and sensory systems Classified as 3 groups: Salamanders Frogs and toads Caecilians (legless, burrow in moist soil and sediment) Ecology of Amphibians Some release toxins as protection Living species have been decreasing