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 • 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 • 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 • 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 conusarteriosus, which directs the blood to the lungs or the body
