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Amphibians
Section 30.2
Animal Classification
Invertebrates
Sponges
Cnidarians
Worms
Mollusks
Arthropods
Echinoderms
- Order Anura
- Order Caudata
- Order Apoda
Animals
Ectotherms
(cold-blooded)
Vertebrates
Fishes
Amphibians
Amphibians
Reptiles
Phylum Chordata
Endotherms
(warm-blooded)
Birds
Mammals
What is an Amphibian?
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Class Amphibia – means “double life”
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Starts life in water and changes on land
Evolutionary advantages over fishes
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Thin, moist skin
Most amphibians have four legs
Lungs
What is an Amphibian?
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Nearly all amphibians rely on water for
reproduction
Undergo external fertilization

Water is needed to transport sperm
Ectotherms
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Ectotherm – an animal that has a variable
body temperature and gets its heat from
external sources (can’t regulate their body
temperature on their own)
Ectotherms
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Amphibians become dormant in regions that
are too hot or cold for part of the year

Many of them burrow into mud and stay there until
suitable conditions return
Metamorphosis
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Tadpoles possess fins, gills, and a twochambered heart as seen in fish
Tadpoles develop legs, lungs, and a threechambered heart to become adults
Metamorphosis
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Young salamanders resemble adults, and
they have gills and usually have a tail fin
Most adult salamanders lack gills and fins

Adult salamanders have no lungs and breathe
only through their skin
Walking Requires More Energy

The evolution of the three-chambered heart
in amphibians ensured that cells received the
proper amount of oxygen
Walking Requires More Energy
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One atrium receives oxygen-rich blood from
the lungs and skin
Another atrium receives oxygen-poor blood
from the body tissues
Blood from both chambers then moves to the
third chamber (or ventricle) which mixes the
two types of blood
Walking Requires More Energy

Because of the mixture of blood, the skin is
much more important than the lungs as an
organ for gas exchange
Walking Requires More Energy

Because the skin of an amphibian must stay
moist to exchange gases, most amphibians
are limited to life on the water’s edge or other
moist areas
Frogs and Toads
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Frogs and toads belong to the order Anura
Frogs have long hind legs and smooth, moist
skin
Toads have short legs and bumpy, thick, dry
skin
Frogs and Toads
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Adult frogs and toads are predators that eat
invertebrates, such as insects and worms
Many species of frogs and toads secrete
chemicals through their skin as a defense
against predators
Frog eating bird
Frogs and Toads
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Frogs and toads also have vocal cords
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Vocal cords – sound-producing bands of tissue in
the throat
As air moves over the vocal cords, they
vibrate and cause molecules in the air to
vibrate
Frogs and Toads

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Tympanic membrane – used for hearing;
amplifies sounds frogs and toads make
Throat pouches and tympanic membranes
increase the loudness of their calls
Frogs and Toads
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Frogs and toads are among the first
organisms to be exposed to pollutants in the
air, on land, or in the water
Declining numbers of frogs species
sometimes indicate the presence of
pollutants in the environment
Salamanders
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A salamander (order Caudata) has a long,
slender body with a neck and tail
Salamanders resemble lizards, but have
smooth, moist skin and lack claws
Salamanders
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The young hatch from eggs, look like small
salamander adults, and are carnivorous
Caecilians
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Caecilians (order Apoda) are burrowing
amphibians, have no limbs, and have a short
(or no) tail
They are tropical animals with small eyes that
often are blind
Caecilians
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They eat earthworms and other invertebrates
found in the soil
All caecilians have internal fertilization
Challenges of Life on Land
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Some dangers living on land
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1. Temperature of water remain fairly constant
while air temperatures can vary greatly
Challenges of Life on Land
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2. Without the support of water, the body was
clumsy and heavy
The legs of a salamander are set at right angles to
the body. This prevent the belly from dragging on
the ground.
Challenges of Life on Land
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Raised trunks from the ground increases
mobility