Amphibians
The double life
Origin and Evolution of Amphibians
• Lobe – finned fish
– Bone structure within their fins allowed for them
to function as “legs”
– Modified pouches in digestive tract evolved into
lungs of the lungfish and swim bladder of modern
fish
– Amphibians also share skull and vertebral column
Lobed – finned fish: Coelocanth
• Oldest amphibian fossils were dated to 360 m.y.a
• Between 359 – 299 m.y.a amphibians split into
two main evolutionary lines
– Modern amphibians
– Ancestors of reptiles
Classification
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Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Amphibia, 4500 species
– Order Anura, largest order contains the frogs and
toads
– Order Caudata, contains salamanders
– Order Gymnophiona, contains caecilians
Order Anura
• Frogs and toads (squat bodies, shorter legs, skin
not as smooth as frog)
• Found in a variety of moist habitats
• Adults are carnivorous
• Reproduction
– Amplexus
• Metamorphosis
Life Cycle
• Fertilization takes place
• Eggs hatch, tadpole lives off yolk stored in its
body
• Tadpole grows larger, three gills develop
• Mouth opens, begins to feed on algae
• Tadpole grows slowing changing from an
aquatic larva into an adult
• May vary depending on species
Metamorphosis
• Process of change from an egg to larva to adult
• Triggered by the hormone thyroxine that is
produced by the thyroid gland
Order Caudata
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Salamanders, newts, mudpuppies
Elongated tails, and smooth, moist skin
Lay eggs in water or moist places
Both young and adult are carnivorous
Hatchlings are small versions of parent except
young have gills
Order Gymnophiona
• Caecilians
• Legless amphibians
• Live in tropical areas, burrow in the soil, also
aquatic
• Lay eggs or young are born alive
Characteristics of Amphibians
• Five key characteristics; legs, lungs, double –
loop circulation, 3 - chambered heart,
cutaneous respiration
• Live in moist habitats
• Mostly external fertilization
Movement
• Skeleton
– Strong endoskeleton
– Vertebrae of the spine is interlocked to form a
rigid structure
– Limbs support body
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Forelimbs attach to the pectoral girdle (shoulder)
Hind limbs attach to the pelvic girdle
Transfers body weight to the limbs
Frogs, lower limbs are fused into a single bone
– Forelimb (radio – ulna) and hind limb (tibiofibula)
Response
• Sense Organs
– Lateral line as larvae
– Sight, sound, smell
– Nictitating membrane
• Transparent membrane that covers eyes
– Tympanic membrane
• Eardrum
Respiration
• Gills, most loose as adults
• Skin serves two important functions –
respiration and protection
– Cutaneous respiration
– Diffusion
– Mucous glands
• Pulmonary respiration
Pulmonary Respiration
• Pump air into lungs in a process called positive
– pressure breathing
• Frog breathes by changing the volume and
pressure of air in its mouth while either
opening or closing its nostrils
Circulation
• Three chambered heart and double – looped
circulation
• Increase pressure and speed of delivery for
oxygen rich blood to organs
• Divided into two separate loops
Two separate loops
• Pulmonary circulation
– Carries deoxygenated blood from the heart to the
lungs and back to the heart
• Systemic circulation
– Carries oxygenated blood from the heart to the
body and back to the heart
Three chambered heart
• Right and Left Atrium (septum divides)
• Ventricle (spongy surface and contraction)
– Deoxygenated blood enters from the body, right atrium
– Oxygenated blood enters from the lungs, left atrium
– Contraction of the atria forces blood into a single
ventricle
– Ventricle contracts pushes all of the blood into the
conus arteriosus, which directs the blood to the lungs
or the body