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