Amphibians
Chapter 40
(798-814)
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Objective 40.1
• Describe three preadaptations involved in
the transition from aquatic to terrestrial life
• Describe two similarities between
amphibians and lobe-finned fishes
• List five characteristics of living
amphibians
• Name the three orders of living
amphibians and give an example of each
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Origin and evolution of amphibians
About 360 million years ago, amphibians
became the first vertebrates to live on
land. The name amphibian comes from
the Greek word meaning “double” and
“life” and reflects the fact that many
amphibians spend part of their life on land
and part in water.
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Adaptation to land
• Most likely evolved from lobe-finned fishes
• Preadaptatins are adaptations in an
ancestral group that allow a shift to new
functions which are later favored by
natural selection
• Fins had bone structure to walk as legs
• Modified pouches in digestive track 
lungs
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Characteristics of early amphibians
• Skull and vertebra column, bones in fin
and (similar)
• Scarcopterygian- extinct lobe-finned fish
• 360million years fossil record
• Had 4 strong limbs
• Gills, teeth, lateral lines
• Most likely spent most time in water
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Diversification of amphibians
•
Devonian period and carboniferous period
amphibians split into 2 main evolutionary lines
• One modern amphibians
• Ancestors of reptiles
• 4500 species of amphibians
3 orders of amphibians
1. O. Anura – frogs and toads (3900 species)
2. O. Caudata- salamanders (400 species)
3. O. Gymnophiona – caecilians (legless tropical)
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Modern Amphibians
• Aquatic larval to terrestrial adult
(metamorphosis)
• Moist thick skin with no scales
• Feet- lack claws, webbed
• Gills, lungs, skin in respiration
• Eggs lack muticellular membranes or
shells
• Eggs laid in water- external fertilization
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Objective 40.2
• Relate the structure of amphibians skin to
the types of habitats in which amphibians
can survive
• Identify three adaptations for the life on
land shown by the skeleton of a frog
• Sequence the flow of blood through an
amphibian’s heart
• Describe the digestive/ excretory systems
• Discuss the nervous system
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Characteristics of amphibians
As you have already seen, terrestrial
vertebrates face challenges that are far
different from those faced by aquatic
vertebrates. In this section you will learn
about some of the ways amphibians meet
the challenges of living on land.
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skin
Two important functions
1. Respiration
2. Protection
Moist, permeable to gases and water
Numerous mucous glands keeps skin moist
Can also secrete- foul taste/ poison
Live in moist areas
Tend to be active at night
Can be affected by environment (indicators)
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skeleton
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Strong internal skeleton
Bear weight of body
Strong limbs to support body
Ability to jump and land
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Circulatory system
2 separate loops
1. Pulmonary circulation- carries
deoxygenated blood from heart to lungs
and back to heart
2. Systemic circulation- carries oxygenated
blood from the heart to the body and
back to the heart
3 chambered heart
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Respiration
• Larval by gills and skin
• Adult – lungs (pulmonary respiration) and
skin (cutaneous respiration)
• Positive pressure breathing- pumps air
into the lungs
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Digestive system
• Carnivorous
• Small insects, arthropods, mice, snakes,
fish, amphibians, birds
• Larva- herbivores (algae, bacteria, plants)
• Pharynx  esophagous  stomach 
liver  gallbladder  small intestine 
large  cloaca
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Excretory system
• Kidney (primary) filter nitrogen and waste
• Flushed out as urine
• Kidney  urinary ducts  cloaca 
urinary bladder (water storage) can be
reabsorbed during dry times
• Transform ammonia into urea
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Nervous system
• Brain (same size as fish)
• Olfactory lobes (sense of smell)
• Long lobes of cerebrum (behavior
learning)
• Optic lobes – process info from eyes
• Cerebellum- muscular coordination
• Medulla oblongata- organ functions, heart
• 10 pairs of cranial nerves
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Sense organs
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Lateral lines (only in water)
Nicitating membrane- covering of eyes
Tympanic membrane- eardrum
Columella- small bone that extends
between the tympanic membrane and the
inner ear
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Objective 40.3
• Explain how a male frog attracts a female
of the same species
• Discuss the reproductive system in frogs
• Describe the changes that occur during
metamorphosis in frogs
• Identify two examples of parental care in
amphibians
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Reproduction in amphibians
• One of the biggest differences between
aquatic and terrestrial life-forms is their
method of reproduction. Most amphibians
depend on water for reproduction. They
lay their eggs in water and spend the early
part of their lives as aquatic larvae.
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Courtship and fertilization
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Mating call- frogs croak
Males have vocal sacs
Female responds to same species
External fertilization
Eggs  tadpoles  hind legs appear 
frog legs appear  young frog  adult
• Thyroxine – produced by thyroid gland to
stimulate metamorphosis
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Parental care
• Parent care can increase chances of
survival
• Male remain with eggs
• Rhinoderma darwinni- takes them in vocal
sacs till hatch
• Gastric –brooding frogs in Australiaswallow eggs
• Eleutherodactylus- sit on eggs
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Virtual Dissections
• http://www.mhhe.com/biosci/genbio/virtual
_labs/BL_16/BL_16.html
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