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30-3 Amphibians
Photo Credit: Animals Animals/©Bill Beatty
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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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3. 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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4. 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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5. 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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6. Evolution of Amphibians
Amphibian Adaptations
Lungs
Pelvic Girdle
Leg Bones: The legs of a land vertebrate must be strong enough to hold its weight.
The characteristics of amphibians include adaptations for living partially on land. For example, lungs enable adult amphibians to obtain oxygen from air.
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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7. Form and Function in Amphibians
The class Amphibia is relatively small and diverse.
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8. Form and Function in Amphibians
Frog Anatomy
This illustration shows the organs of a frog’s digestive system.
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9. Form and Function in Amphibians
Mouth
Esophagus
In a frog’s digestive system, food slides down the esophagus into the stomach.
Stomach
This illustration shows the organs of a frog’s digestive system.
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10. Form and Function in Amphibians
The breakdown of food begins in the stomach and continues in the small intestine.
Stomach
Small intestine
This illustration shows the organs of a frog’s digestive system.
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11. Form and Function in Amphibians
The liver, pancreas, and gallbladder secrete substances that aid in digestion.
Gallbladder
Liver
Pancreas
This illustration shows the organs of a frog’s digestive system.
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12. 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
This illustration shows the organs of a frog’s digestive system.
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13. 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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14. Form and Function in Amphibians
Amphibian Circulation and Excretion
Heart
Lung
Kidney
Ureter
Urinary bladder
Cloaca
Like all vertebrates, amphibians have a circulatory system and an excretory system. An amphibian’s heart has three chambers—two atria and one ventricle. Although some wastes diffuse across the skin, kidneys remove most wastes from the bloodstream.
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15. Form and Function in Amphibians
Frog Metamorphosis
Adult Frog
Fertilized eggs
Young Frog
An amphibian typically begins its life in the water, then moves onto land as an adult. This diagram shows the process of metamorphosis in a frog.
Tadpoles
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16. 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.
An amphibian typically begins its life in the water, then moves onto land as an adult.
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17. Form and Function in Amphibians
Frog’s Sense Organs
Photo Credit: Animals Animals/©Bill Beatty. A frog’s eyes and ears are among its most important sensory organs. Transparent eyelids called nictitating membranes protect the eyes underwater and keep them moist in air. Tympanic membranes receive sound vibrations from air as well as water.
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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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30-3
The word amphibian refers to the ability to
live in hot climates.
live in wet places.
live both in water and on land.
live in cold and hot climates.
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30-3
Fossil evidence indicates the first land amphibians appeared during the
Jurassic Period.
Devonian Period.
Cambrian Era.
Cretaceous Era.
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30-3
In a larval amphibian, gas exchange occurs through
the skin only.
both the skin and the gills.
the gills only.
in a lung.
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30-3
The tympanic membrane in a frog enables it to
hear.
see.
smell.
taste.
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30-3
Which of the following is a group of amphibians living on the Earth today?
crocodiles
snakes
salamanders
lizards
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