Amphibians
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: February 12, 2015
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C HAPTER
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Chapter 1. Amphibians
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Amphibians
Give examples of amphibians.
Describe the characteristics of the amphibians.
Describe amphibian adaptations for life on land.
Summarize amphibian habitats.
What were the first land vertebrates?
Amphibians! In order for water-dwelling animals to adapt to life on land, many new adaptations had to take place.
First, they needed to be able to breathe air instead of obtaining oxygen from water. And fins don’t work well as legs!
They needed to be able to move around well on land.
Characteristics of Amphibians
What group of animals begins its life in the water, but then spends most of its life on land? Amphibians! Amphibians
are a group of vertebrates that has adapted to live in both water and on land. Amphibian larvae are born and live in
water, and they breathe using gills. The adults live on land for part of the time and breathe both through their skin
and with their lungs.
There are approximately 6,000 species of amphibians. They have many different body types, physiologies, and
habitats, ranging from tropical to subarctic regions. Frogs, toads, salamanders ( Figure 1.1), newts, and caecilians
are all types of amphibians.
How did Amphibians Adapt to Living on Land?
In order to live on land, amphibians replaced gills with another respiratory organ, the lungs. Other adaptations
include:
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FIGURE 1.1
One of the many species of amphibian is
this dusky salamander.
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Skin that prevents loss of water.
Eyelids that allow them to adapt to vision outside of the water.
An eardrum developed to separate the external ear from the middle ear.
A tail that disappears in adulthood (in frogs and toads).
Classification of the Amphibians
Like fish, amphibians are ectothermic vertebrates. They belong to the class Amphibia. There are three orders:
1. Urodela, containing salamanders and newts.
2. Anura, containing frogs and toads.
3. Apoda, containing caecilians.
Where do Amphibians Live?
Most amphibians live in fresh water, not salt water. Their habitats can include areas close to springs, streams, rivers,
lakes, swamps and ponds. They can be found in moist areas in forests, meadows and marshes. Amphibians can
be found almost anywhere there is a source of fresh water. Although there are no true saltwater amphibians, a few
can live in brackish (slightly salty) water. Some species do not need any water at all, and several species have also
adapted to live in drier environments. Most amphibians still need water to lay their eggs.
How do Amphibians Reproduce?
Amphibians reproduce sexually. The life cycle of amphibians happens in the following stages:
1. Egg Stage: Amphibian eggs are fertilized in a number of ways. External fertilization, employed by most
frogs and toads, involves a male gripping a female across her back, almost as if he is squeezing the eggs out of
her. The male releases sperm over the female’s eggs as they are laid. Another method is used by salamanders,
whereby the male deposits a packet of sperm onto the ground. The female then pulls it into her cloaca, a single
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Chapter 1. Amphibians
opening for her internal organ systems. Therefore, fertilization occurs internally. By contrast, caecilians and
tailed frogs use internal fertilization, just like reptiles, birds, and mammals. The male deposits sperm directly
into the female’s cloaca.
2. Larval stage: When the egg hatches, the organism is legless, lives in water, and breathes with gills.
3. During the larval stage, the amphibian slowly transforms into an adult by losing its gills and growing four
legs. Once development is complete, it can live on land.
Summary
• Amphibians live in both water and on land; amphibian larvae are born and live in water, and they breathe using
gills. The adults live on land for part of the time and breathe both through their skin and with their lungs.
• Adaptations for land in amphibians include protective skin and eyelids that allow them to adapt to vision
outside of the water.
Explore More
Use the resources below to answer the questions that follow.
Explore More I
• San Diego Zoo Amphibians at http://kids.sandiegozoo.org/animals/amphibians
1. Describe the skin of an amphibian.
2. What is metamorphosis?
3. What is meant by "ectothermic"? How does this affect an animals behavior?
Explore More II
• Respiratory Organs In Amphibians at http://www.youtube.com/watch?v=Nfojq4ikHH0 (3:29)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57378
1. How do frogs fill their lungs?
2. Why do amphibians need less oxygen than birds or mammals?
3. How do frogs breathe when they are underwater?
Review
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List three adaptions amphibians have for life on land?
List four examples of amphibians.
How do amphibians reproduce?
Describe the amphibian larval stage. What changes occur during this stage?
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References
1. Kerry Wixted. A dusky salamander is an amphibian . CC BY 2.0
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