AMPHIBIANS Amphibian Means Double Life The spend part
AMPHIBIANS
Amphibian • Means Double Life – The spend part of their lives in water and part on the land. – They have to return to the water to lay the eggs. Eggs are not covered by hard waterretaining covering. Jelly-like easily dehydrated.
Amphibian • Yong amphibians go thru a larval aquatic form. i. e. tadpole. • “Ontogeny recapitulates phylogeny” • Hints that the amphibians evolved from a fish like ancestor • ‘phibs may represent a step in evolution from water vertebrates to land vertebrates.
Origins of Amphibians • First land vertebrates appeared approx. 325 million years ago. Periodic droughts caused the survival of fish species that could withstand dry conditions. • Amphibians dominated the earth during the first 100 million years of their existence. Then the reptiles evolved. Amphibian numbers then drastically declined. • Lungfish: Link between fish and amphibians.
General Amphibian Characteristics • Larval forms similar to fish in structure and form (gills, fins) • Development to maturity (metamorphosis) causes characteristics that enable them to survive on land. – – – – All metamorphosis Eggs laid in water. Fertilized externally Smooth, thin, usually moist skin Feet often webbed. No claws on feet. Larval forms herbivorous. Adults carnivorous Respire thru gills, lungs, and/or skin Larvae have a two chambered heart (so did the fish) Adult have 3 chambered hearts
Classification • 3 Living Orders: – A. Apoda: Wormlike. Legless – B. Urodela: Salamanders and Newts. Retain tails throughout life. – C. Anura: Frogs and toads. No tails in adult forms.
Frogs vs. Toads: • Found on every continent except Antarctica • Frogs have smooth, moist skin. Usually live near water. • Toads have drier, rough or warty skin. Usually land dwellers. • Tadpoles: larval form • Frogs and toads economically valuable. Eat insects. • May be indicators of air quality and ozone condition. Populations of frogs have decreased in number in the past decade; possibly due to the depletion of the ozone layer.
Frogs: • Adaptations to life on land: – Camouflage – Strong back legs for jumping – Tongue attached to front of ventral surface of mouth. Sticky and able to be sent out of mouth to catch insects. – Tympanum present (external eardrum on head) – Respire through moist skin, lungs. – Males have vocal cords for communication (attracts mates) – Eyelids keep eyes moist (3 Pair)
Adaptations to Life in Water • • • Counter shading (dark dorsal, light ventral surface) Tympanum Dorsal eyes, external nares (nostrils) Strong back legs for swimming (webbed) 3 rd eyelid (nictitating membrane). Act as swim goggles. Allows frog to see underwater Able to seal off external nares to internal nares. Efficient digestive and excretory systems Metamorphosis controlled by genes Larval forms able to regenerate a developing limb or tail.
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