Chapter 3
Amphibians: The First Terrestrial Vertebrates
Evolutionary Perspective
• Domain: Eukarya • Kingdom: Animalia • Phylum: Chordata • Class: Amphibia
• Live both in water and on land • Tetrapods - 4 muscular limbs with fingers
and toes
Skin
• Protects against infective organisms and UV light
• No covering (scales, feathers, hair) • Many have glands to maintain moisture • Some glands produce toxins or other chemicals • Chromatophores - skin cells that allow color
change
Skeleton
• Skeleton provides support against gravity • Skull
• Flattened, small, few bony elements • Lighter than fish
• Jaw structure • Allows for crushing of food
• Vertebral column • Allows for support and flexibility on land
Digestive System
• Adult amphibians are carnivores • Most larvae are herbivores • Prey located by sight • Tongue
• Attaches anteriorly to jaw • Folds on floor of mouth • Glands (mucous and buccal) at tip of tongue
provides sticky secretion
Circulation and Respiration
• 3 chambered heart • Ventricle • 2 atria
• Cutaneous respiration • Gas exchange across the skin • Occurs in water or on land • 30-90 % of total gas exchange
• Buccopharyngeal respiration • Gas exchange across the
surfaces of mouth and pharynx • 1-7 % of total gas exchange
• Lungs • Contribute more to gas exchange
as temperature or metabolic activity increases
• Requires buccal pump • External gills
• Present in larvae and some adults
Temperature Regulation
• Ectothermic - cold-blooded • Behaviors can regulate temperature • Basking • Some are nocturnal • Temperature ranges
• Salamanders: -2 to 27 degrees C • Frogs and toads: 3 to 41 degrees C
Nervous system• Lateral line system
• Respond to vibration • Present in larvae and some adults
• Chemoreception • Used in mate recognition, detecting
chemicals and food • Vision
• Primary way to locate food • Nictitating membrane moveable lower
eyelid
• Hearing • Ears - tympanic membrane, middle ear and
inner ear • Tympanic membrane - recieves vibration and
transmits them to middle ear