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Biology
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30-3 Amphibians
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30-3 Amphibians
What Is an Amphibian?
What Is an Amphibian?
An amphibian is a vertebrate that, with
some exceptions:
• lives in water as a larva and on land as
an adult
• breathes with lungs as an adult
• has moist skin that contains mucous
glands
• lacks scales and claws
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30-3 Amphibians
Evolution of Amphibians
Evolution of Amphibians
The first amphibians appeared in the late
Devonian Period, about 360 million years ago.
The transition from water to land required
that the terrestrial vertebrates had to:
• breathe air,
• protect themselves and their eggs from
drying out, and
• support themselves against the pull of
gravity.
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Evolution of Amphibians
Early amphibians evolved several
adaptations that helped them live at least
part of their lives out of water.
Bones in the limbs and limb girdles of
amphibians became stronger, permitting
more efficient movement.
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Evolution of Amphibians
Lungs and breathing tubes enabled
amphibians to breathe air.
The sternum formed a bony shield to
support and protect internal organs,
especially the lungs.
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Evolution of Amphibians
Amphibian Adaptations
Lungs
Pelvic Girdle
Leg Bones:
The legs of a land
vertebrate must be
strong enough to hold
its weight.
Skin: The skin and the lining of
the mouth cavity of many adult
amphibians are thin and richly
supplied with blood vessels.
Watery mucus is secreted by
glands in the skin.
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Form and Function in Amphibians
Form and Function in Amphibians
The class Amphibia is relatively small and
diverse.
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Form and Function in Amphibians
Frog Anatomy
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Form and Function in Amphibians
Mouth
In a frog’s digestive
system, food slides down
the esophagus into the
stomach.
Esophagus
Stomach
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Form and Function in Amphibians
The breakdown of food
begins in the stomach
and continues in the
small intestine.
Small intestine
Stomach
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Form and Function in Amphibians
The liver, pancreas, and
gallbladder secrete
substances that aid in Gallbladder
digestion.
Liver
Pancreas
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Form and Function in Amphibians
At the end of the large
intestine is a muscular
cavity called the cloaca,
through which digestive
wastes, urine, and eggs
or sperm leave the body.
Large
intestine
(colon)
Cloaca
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Form and Function in Amphibians
Respiration
In most larval amphibians, gas exchange occurs
through the skin and the gills.
Adult amphibians typically respire using lungs,
but some gas exchange occurs through the skin
and the lining of the mouth.
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Amphibian
Circulation
and Excretion
Form and Function in Amphibians
Heart
Lung
Kidney
Ureter
Urinary
bladder
Cloaca
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Form and Function in Amphibians
Frog Metamorphosis
Adult
Frog
Fertilized
eggs
Young
Frog
Tadpoles
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Form and Function in Amphibians
Adults are typically ready to breed in about one
to two years.
Frog eggs are laid in water and undergo external
fertilization.
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Form and Function in Amphibians
Frog’s Sense Organs
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Groups of Amphibians
Groups of Amphibians
The three groups of amphibians alive
today are:
• salamanders
• frogs and toads
• caecilians
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Groups of Amphibians
Salamanders
Salamanders and newts have long bodies and
tails.
Most have four legs.
Both adults and larvae are carnivores.
Adults usually live in moist woods, where they
tunnel under rocks and rotting logs.
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Groups of Amphibians
Frogs and Toads
Frogs and toads have the ability to jump.
Frogs tend to have long legs and make lengthy
jumps.
Toads have relatively short legs and are limited to
short hops.
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Groups of Amphibians
Caecilians
Caecilians are legless animals that live in water or
burrow in moist soil or sediment.
Caecilians feed on small invertebrates such as
termites.
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30-3
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Continue to:
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The word amphibian refers to the ability to
a. live in hot climates.
b. live in wet places.
c. live both in water and on land.
d. live in cold and hot climates.
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30-3
Fossil evidence indicates the first land
amphibians appeared during the
a. Jurassic Period.
b. Devonian Period.
c. Cambrian Era.
d. Cretaceous Era.
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In a larval amphibian, gas exchange occurs
through
a. the skin only.
b. both the skin and the gills.
c. the gills only.
d. in a lung.
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The tympanic membrane in a frog enables it to
a. hear.
b. see.
c. smell.
d. taste.
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Which of the following is a group of amphibians
living on the Earth today?
a. crocodiles
b. snakes
c. salamanders
d. lizards
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