Download Ch. 30.3

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