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Biology
Chapter
25 - Early Tetrapods and Amphibians
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Amphibians - first land animals
Animals that have
gills and lungs during
their life cycle…
“transition animals” From Water to Land
Movement from water to
land is perhaps the most
dramatic event in animal
evolution
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Amphibians
Ch. 25Amphibians
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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Amphibians
Ch. 25Amphibians
Evolution of Amphibians
How are amphibians adapted for life
on land? How have they evolved?
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Amphibians
Ch. 25Amphibians
Evolution of Amphibians
Lobe-finned fishes (lungfish)
are the sister group to tetrapods
Differences in the Tetrapods:
Have stronger backbone
Muscles to support the body in air
Muscles to elevate the head
Stronger shoulder and hip girdles
More protective rib cage
Modified ear structure to detect airborne sounds
Foreshortening of skull
Longer snout
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Amphibians
Ch. 25Amphibians
Evolution of Amphibians
Evolution of Amphibians
The first amphibians appeared 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
• support themselves against the pull of gravity
Vascular plants, pulmonate snails, and tracheate arthropods made
transition earlier
Amphibians only living vertebrates that have a transition from water to
land in their development
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Amphibians
Ch. 25Amphibians
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.
REASONS for Adapatations:
Air is 1000 times less dense
• Provides less buoyancy than water
• Limbs and skeleton must support more weight
Air fluctuates in temperature more rapidly than water
• Animals must adjust to these extremes
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Amphibians
Ch. 25Amphibians
Evolution of Amphibians
Showing evolutionary link
to fossil record. “Missing Link”
organanism from water (fish)
to land (tetrapods).
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Amphibians
Ch. 25Amphibians
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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Amphibians
Ch. 25Amphibians
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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Amphibians
Ch. 25Amphibians
Evolution of Amphibians
In many adult amphibians, the internal surfaces of the
lungs are richly supplied with blood vessels and folds
that increase surface area.
Lungs
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Form and Function in Amphibians
The class Amphibia is relatively small and diverse.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Feeding
Tadpoles are typically filter feeders or herbivores
that graze on algae.
Their intestines help break down hard-to-digest
plant material and are usually filled with food.
The feeding apparatus and digestive tract of adults
are meat-eating structures.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Frog Anatomy
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Adult amphibians are almost entirely carnivorous.
Many salamanders and frogs have long, sticky
tongues specialized to capture insects.
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Amphibians
Ch. 25Amphibians
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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Amphibians
Ch. 25Amphibians
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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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
The liver, pancreas, and
gallbladder secrete
substances that aid in Gallbladder
digestion.
Liver
Pancreas
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Amphibians
Ch. 25Amphibians
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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Amphibians
Ch. 25Amphibians
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.
SKIN:
Thin skin loses water rapidly
Restricts terrestrial forms to moist habitats
Ectotherms
Body temperature depends on environment and restricts range
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Circulation
In frogs and other adult amphibians, the circulatory
system forms a double loop.
The first loop carries oxygen-poor blood from the
heart to the lungs and skin, and takes oxygen-rich
blood from the lungs and skin back to the heart.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
The second loop transports oxygen-rich blood from
the heart to the rest of the body, and carries oxygenpoor blood from the body back to the heart.
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Amphibians
Ch. 25Amphibians
Amphibian
Circulation and
Excretion
Form and Function in Amphibians
Heart
Lung
Kidney
Ureter
Urinary
bladder
Cloaca
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
The amphibian heart has three separate chambers:
•left atrium
•right atrium
•ventricle
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
To body,
lungs and
skin
Amphibian
Heart
From
Body
To body,
lungs and
skin
From
Lungs
Left
atrium
Right
atrium
Ventricle
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Excretion
Amphibians have kidneys that filter wastes from
the blood.
Urine travels through tubes called ureters into the
cloaca.
Urine is then passed directly to the outside, or
temporarily stored in a small urinary bladder just
above the cloaca.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Reproduction
In most species of amphibians, the female lays
eggs in water, then the male fertilizes them
externally.
In a few species, including most salamanders,
eggs are fertilized internally.
After fertilization, frog eggs are encased in a sticky,
transparent jelly.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
The jelly attaches the egg mass to underwater plants
and makes the eggs difficult for predators to grasp.
The yolks of the eggs nourish the embryos.
Most amphibians abandon their eggs after they lay
them.
A few amphibians take care of both eggs and young.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Frog Metamorphosis
Adult
Frog
Fertilized
eggs
Young
Frog
Tadpoles
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Amphibians
Ch. 25Amphibians
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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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
The fertilized eggs hatch into tadpoles a few days
to several weeks later.
Fertilized eggs
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Amphibians
Ch. 25Amphibians
Tadpoles gradually
grow limbs, lose their
tails and gills, and
become meat-eaters
as they develop into
terrestrial adults.
Form and Function in Amphibians
Young frog
Tadpole
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Movement
Amphibian larvae move by wiggling their bodies
and using a flattened tail for propulsion.
Adult salamanders walk or run.
Frogs and toads, have well-developed hind limbs
that enable them to jump long distances.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Response
Amphibians have well-developed nervous and
sensory systems.
An amphibian's eyes are protected from damage
and kept moist by a transparent nictitating
membrane.
This membrane is located inside the regular eyelid
and can be closed over the eye.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Amphibians hear through tympanic membranes, or
eardrums, located on each side of the head.
Many amphibian larvae and adults have lateral line
systems that detect water movement.
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Amphibians
Ch. 25Amphibians
Form and Function in Amphibians
Frog’s Sense Organs
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
What are the main groups of living
amphibians?
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Groups of Amphibians
The three groups of amphibians alive
today are:
• Salamanders (Order Urodela)
• frogs and toads (Order Anura)
• Caecilians (Order Gymnophiona)
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Salamanders Order Caudata
(Urodela)
Salamanders and newts have long bodies and tails.
Most have four legs, @ right angles to body.
Respiration can occur through salamander skin, and lungs
Both adults and larvae are carnivores.
Adults usually live in moist woods, where they tunnel under
rocks and rotting logs.
Internal Fertilization: Female recovers in cloaca a
spermatophore deposited on a leaf or stick
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Ch. 25Amphibians
Groups of Amphibians
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Ch. 25Amphibians
Groups of Amphibians
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Larval Salamander
Red-Spotted Newt: Aquatic larva metamorphoses into red-eft, which
remains on land for 1-3 years, until becoming secondary aquatic adult.
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Salamanders and Paedomorphosis
Descendants retain into adulthood features that were
present in larval stages of ancestors
2 species of salamanders that
exhibit paedomorphosis.
They both have their gills during
their life cycle.
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Frogs and Toads - Order Anura (Salientia)
All have a tailed larval stage and tailless, jumping adults
(except for 1 species - Ascaphus)
Frogs and toads have the ability to jump.
Toads have thicker skin, covered in “warty” projection
glands that secrete poison. The poison is only harmuful if
swallowed or gets in your eyes.
Must live near water source
Reproduction mode requires water
Skin is water-permeable skin
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Coastal Tailed Frog
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Tree Frog

44 families of frogs and toads
Family Ranidae
common larger frogs
in North America
Family Hylidae
Includes the tree frogs
Family Bufonidae (toads)
Contains toads with
thicker skins and prominent warts
Frogs
Conraua goliathLargest frog
Toad
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Ch. 25Amphibians
Groups of Amphibians
African Clawed Frog - has been introduced to California, and is now a
huge pest. Aggressive and has caused a decline in native frogs. Similar
to when huge toads were introduced to Australia.
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Epidermis has two types of integumentary glands
•Mucous glands secrete protective waterproofing
•Large serous glands produce a whitish, watery poison
Dendrobatid frogs of South America secrete highly toxic skin
poisons
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Skeleton of frog: notice human similarities and differences.
Feet - 5 digits, hand - 4 digits
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Respiration in frogs:
No diaphragm to help, instead use
pressure within cavities.
A. Force mouth down, air moves
into mouth thru nostrils
A. Force mouth up, air forced into lungs
B. Mouth ventilates
C. Muscles in abdominal wall and
recoiling of lungs forces air out.
Most Carbon Dioxide is lost through
the skin, not lungs.
Vocal cord more developed in males.
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Caecilians - Order Gymnophiona
Caecilians are legless animals that live in water or burrow
in moist soil or sediment.
Caecilians feed on small invertebrates such as termites.
Found in S.America, Africa, India
Have vertebrae and long ribs.
Many have fishlike scales embedded in their skin.
Internal Fertilization.
Most Oviparous, although some viviparous (young feed on
walls of oviduct).
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Amphibians
Ch. 25Amphibians
Groups of Amphibians
Female coiled around eggs
Pink headed caecilian- W.Africa
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Ch. 25- Amphibians
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Click to Launch:
Continue to:
- or -
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Ch.
25- Amphibians
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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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Ch.
25- Amphibians
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Amphibians that maintain their ancestral larval
forms throughout life (paedomorphosis) are
a. Caecilians
b. Mud Puppies
c. Salamanders
d. Toads
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Ch.
25- Amphibians
30-3
In a larval amphibians, gas exchange occurs
through
a. both the lungs and the skin.
b. both the skin and the gills.
c. the gills only.
d. in a lung.
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Ch.
25- Amphibians
30-3
The tympanic membrane in a frog enables it to
a. hear.
b. see.
c. smell.
d. taste.
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Ch.
25- Amphibians
30-3
Which of the following is the order for
salamanders?
a. Anura
b. Apoda
c. Caudata
d. Caecilians
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