Synopsis of Amphibians:

• Skeleton: Skull often has many dermal bones; parts of chondrocranium remain unossified; no secondary palate. Vertebrae number from 10 to 200. Vertebrae more differentiated than in fish - for example, skull articulates with specialized cervical vertebra, and pelvic girdle is attached to specialized sacral vertebra. Some amphibians have a sternum (not present in fish), and some have ribs; but in no case do the ribs contact the sternum.
• Circulation: Three-chambered heart, but some separation of oxygenated and deoxygenated blood. Ventricle undivided, but atria separated by septum, ventricle has deep pockets, and conus divided into systemic and pulmonary vessels. Blood from body enters sinus venosus, passes to right side of ventricle, thence out to lungs. Oxygenated blood from lungs enters left atrium, goes to left side of ventricle, then out through systemic part of conus.
• Respiration: Most amphibians have lungs, but supplement oxygenation with dermal capillary network. Inflation of lungs is by contraction of throat, not expansion of body cavity. Gills, when present, are dermal.
• Kidneys: Ophistonephric, as in fishes. Since most amphibians are freshwater, nephrons are well-developed. New type of bladder arises in amphibians: unlike the fish bladder which is an enlargement of the lower end of the archinephric duct, the bladder in amphibians is an outgrowth of the cloacal floor.
• Skin: Most amphibians lack scales. Skin contains numerous mucus glands to keep it soft and moist for respiration. The skin is periodically shed in molts.
• Reproduction: Fertilization usually external, with eggs deposited in water. In more terrestrial amphibians, brooding occurs in various forms, along with reduction of larval phase. In all cases development is fishlike: eggs are non-cleidoic and embryos are anamniotic.

• SUBCLASS Apsidospondyli
  • SUPERORDER Labyrinthodonta: Labyrinthodonts. Extinct.
    • ORDER Temnospondyli
    • ORDER Anthracosauria
  • SUPERORDER Salientia: Mostly modern specialized amphibians. Braincase not well ossified. Ribs generally lacking.
    • ORDER Proanura: Exinct.
    • ORDER Anura: Frogs and toads
      • FAMILY Ranidae: True frogs
      • FAMILY Bufonidae: Toads
• SUBCLASS Lepospondyli
  • ORDER Caudata (Urodela): Salamanders
    • FAMILY Salamandridae: Newts
    • FAMILY Proteidae: Mudpuppies
  • ORDER Gymnophiona (Apoda)
    • FAMILY Caeciliidae: caecilians