Amphibians

AmphibiansAmphibians
Copyright CmassengaleCopyright Cmassengale

Evolution ofEvolution of

"Amphibian" comes from the"Amphibian" comes from the
Greek meaning "both life".Greek meaning "both life".
Amphibians can live on water andAmphibians can live on water and
on land.on land.
Scientist infer that amphibiansScientist infer that amphibians
evolved from lobe-finned fishesevolved from lobe-finned fishes
called crossopterygians.called crossopterygians.

CrossopterygianCrossopterygian

Biologist conclude that amphibians appearedBiologist conclude that amphibians appeared
during the late Devonian period, about 345during the late Devonian period, about 345
million years ago.million years ago.

Crossopterygians had noCrossopterygians had no gills but theygills but they
had internal nostrils and a primitive lunghad internal nostrils and a primitive lung
that may have enabled them then tothat may have enabled them then to
respire for periods of time on land.respire for periods of time on land.

CharacteristicsCharacteristics
of Amphibiansof Amphibians

Amphibians are cold-blooded, whichAmphibians are cold-blooded, which
means their blood temperature risesmeans their blood temperature rises
and falls with that of the surroundingand falls with that of the surrounding
environmentenvironment
••

They use gills, lungs, skin, andThey use gills, lungs, skin, and
mouth cavity in respiration.mouth cavity in respiration.

They have moist, smooth, thin skin with noThey have moist, smooth, thin skin with no
scales.Feet are webbed and the toes lackscales.Feet are webbed and the toes lack
clawsclaws..

Amphibians have many prominent characteristics thatAmphibians have many prominent characteristics that
are adaptations to a life spent both on land and inare adaptations to a life spent both on land and in
water:water:
They change from an aquatic larval stage to aThey change from an aquatic larval stage to a
terrestrial adultterrestrial adult
form. This transformation is called metamorphosisform. This transformation is called metamorphosis

Amphibians enter a state ofAmphibians enter a state of
dormancy or torpor whendormancy or torpor when
conditions are unfavorable.conditions are unfavorable.
They often bury themselves inThey often bury themselves in
mud or leaves, emerging whenmud or leaves, emerging when
conditions are better.conditions are better.Copyright CmassengaleCopyright Cmassengale

Such states of inactivitySuch states of inactivity
are known as known as:are known as known as:
 Hibernation when itHibernation when it
occurs in the winteroccurs in the winter
Estivation when it occursEstivation when it occurs
in the summerin the summer

Larvae have two-chambered hearts;Larvae have two-chambered hearts;
adults have three-chambered heartsadults have three-chambered hearts
and well-developed circulation.and well-developed circulation.

Eggs lack multicellular membranesEggs lack multicellular membranes
or shells. They are usually laid inor shells. They are usually laid in
water or in a moist environment andwater or in a moist environment and
fertilized externally.fertilized externally.

Classification ofClassification of

Biologists have identified aboutBiologists have identified about
2,375 living species of amphibians2,375 living species of amphibians
and have classified them into fourand have classified them into four
ordersorders
Anura – Frogs & ToadsAnura – Frogs & Toads
Urodela – SalamandersUrodela – Salamanders
Trachystoma – Mud eelsTrachystoma – Mud eels
Apoda - CaecilliansApoda - Caecillians

Frogs and toads make up theFrogs and toads make up the
Order Anura ("without a tail").Order Anura ("without a tail").

Salamanders and otherSalamanders and other
amphibians with legs and tailsamphibians with legs and tails
make up the Order Urodelamake up the Order Urodela
("visible tail").("visible tail").

..Some aquatic amphibians (mud eelsSome aquatic amphibians (mud eels
& sirens) belong to the Order& sirens) belong to the Order
Trachystoma ("rough mouth")Trachystoma ("rough mouth")

SirenSiren

Apoda includes caecilians, aApoda includes caecilians, a
tropical, burrowing worm-liketropical, burrowing worm-like
amphibians that is oftenamphibians that is often
LeglessLegless

AnuranAnuran

Frogs and toads comprise theFrogs and toads comprise the
order Anuraorder Anura
There are about 3,500 knownThere are about 3,500 known
species of frogs and 300 kindsspecies of frogs and 300 kinds
of toadsof toads
They are found on everyThey are found on every
continent except Antarcticacontinent except Antarctica

Some types spend their entire lifeSome types spend their entire life
in or near water, but others livein or near water, but others live
mainly on land and come to themainly on land and come to the
water only to matewater only to mate

Some frogs and toads are climbersSome frogs and toads are climbers
that dwell in trees or burrowersthat dwell in trees or burrowers
that live underground.that live underground.

Toads and frogs have manyToads and frogs have many
similarities in the way they look.similarities in the way they look.
Some basic differences betweenSome basic differences between
them are: toads have dry, wartythem are: toads have dry, warty
skin, while frogs have smooth, wetskin, while frogs have smooth, wet
skin.skin.

Both frogs and toads return to water toBoth frogs and toads return to water to
reproduce. In nearly all species eggs arereproduce. In nearly all species eggs are
fertilized externally. The fertilized eggsfertilized externally. The fertilized eggs
hatch into swimming larval forms calledhatch into swimming larval forms called
tadpolestadpoles

UrodelanUrodelan

Salamanders, typical members ofSalamanders, typical members of
the Order Urodela, have elongatedthe Order Urodela, have elongated
bodies, long tails, and smooth,bodies, long tails, and smooth,
moist skinmoist skin

Compared to the anurans, salamandersCompared to the anurans, salamanders
are less able to remain on dry land,are less able to remain on dry land,
although some can live in dry areas byalthough some can live in dry areas by
remaining inactive during the dayremaining inactive during the day

Salamander lay their eggs in waterSalamander lay their eggs in water
and like anurans they hatch intoand like anurans they hatch into
swimming larvaswimming larva
Salamander eggsSalamander eggs

Other species can reproduce inOther species can reproduce in
damp land environments. Eggsdamp land environments. Eggs
laid on land hatch into miniaturelaid on land hatch into miniature
adult salamandersadult salamanders
Marbled SalamanderMarbled Salamander

ApodanApodan

Caecilians, members of the OrderCaecilians, members of the Order
Apoda, compose a highly specializedApoda, compose a highly specialized
group of tropical burrowinggroup of tropical burrowing
amphibiansamphibians

 These legless wormlikeThese legless wormlike
creatures average 30 cm long,creatures average 30 cm long,
but they can be up to 1.3mbut they can be up to 1.3m
long.long.
 They have very small eyes andThey have very small eyes and
are often blind.are often blind.
 They eat worms and otherThey eat worms and other
invertebratesinvertebrates

The caecilian male deposits spermThe caecilian male deposits sperm
directly into the female, and thedirectly into the female, and the
female bears live youngfemale bears live young

TrachystomaTrachystoma

The Order Trachystoma containsThe Order Trachystoma contains
three living species of mud eels,three living species of mud eels,
or sirensor sirens..
Sirens live in the eastern UnitedSirens live in the eastern United
States and northeasternStates and northeastern
Mexico.Mexico.

Frog ExternalFrog External
AnatomyAnatomy

The frog's powerful hind legs areThe frog's powerful hind legs are
equally effective in jumping orequally effective in jumping or
swimming. On land frogs sit withswimming. On land frogs sit with
their hind legs folded against thetheir hind legs folded against the
body, poised to jump at the firstbody, poised to jump at the first
sign of dangersign of danger..
Most frogs can make leaps manyMost frogs can make leaps many
times their body lengthtimes their body length

Frog's eyes also work equally well in orFrog's eyes also work equally well in or
out of water. Because the eyes bulgeout of water. Because the eyes bulge
out from the head, the frog can stayout from the head, the frog can stay
submerged while literally "keeping an eyesubmerged while literally "keeping an eye
out" for predatorsout" for predators

Eyelids that can blink protect theEyelids that can blink protect the
frog's eyes from dust andfrog's eyes from dust and
dehydrationdehydration
In addition to upper and lower eyelids,In addition to upper and lower eyelids,
a third, transparent eyelid called aa third, transparent eyelid called a
nictitating membrane covers eachnictitating membrane covers each
eyeball and joins the lower eyelideyeball and joins the lower eyelid
This membrane keeps the eyelidThis membrane keeps the eyelid
moist and protects it when it ismoist and protects it when it is
under waterunder water

Frogs have eardrums, orFrogs have eardrums, or
tympanic membranes, which aretympanic membranes, which are
circular structures locatedcircular structures located
behind each eyebehind each eye
Tympanic membrane

The frog's thick, moist skinThe frog's thick, moist skin
serves two important functions—serves two important functions—
respiration and protectionrespiration and protection
Glands secrete mucus to keep itGlands secrete mucus to keep it
from drying upfrom drying upCopyright CmassengaleCopyright Cmassengale

Some glands secrete foul-tasting orSome glands secrete foul-tasting or
poisonous substances that protectpoisonous substances that protect
the frog from enemiesthe frog from enemies

Some frogs, such asSome frogs, such as HylaHyla
versicolor,versicolor, can change color incan change color in
order to blend with theorder to blend with the
environment.environment.
Count the
number of
frogs in the
picture?

Frog InternalFrog Internal
AnatomyAnatomy

Skeletal SystemSkeletal System
The frog's spine hasThe frog's spine has
nine vertebraenine vertebrae
The cervicalThe cervical
vertebra at thevertebra at the
anterior end of theanterior end of the
spine allows neckspine allows neck
movement that helpsmovement that helps
frogs catch preyfrogs catch prey

Posterior to thisPosterior to this
are seven trunkare seven trunk
vertebrae, andvertebrae, and
then a single sacralthen a single sacral
vertebra thatvertebra that
supports the hindsupports the hind
legslegs
A long, slim boneA long, slim bone
called the urostylecalled the urostyle
extends from theextends from the
sacral vertebrasacral vertebra

Bones of the pectoralBones of the pectoral
girdle, which form thegirdle, which form the
shoulders, connect toshoulders, connect to
the front legsthe front legs
They also provide theThey also provide the
primary protection toprimary protection to
the internal organs,the internal organs,
since the frog has nosince the frog has no
ribsribs
The pelvic girdleThe pelvic girdle
connects to the hindconnects to the hind
legslegs

Digestive SystemDigestive System

Most frogs feed on insects, and theirMost frogs feed on insects, and their
digestive system is adapted to their dietdigestive system is adapted to their diet
A frog's tongue is an excellent insectA frog's tongue is an excellent insect
catchercatcher.. The frog simply flicks out itsThe frog simply flicks out its
long sticky tongue, curls it around itslong sticky tongue, curls it around its
prey, and pulls the insect back into itsprey, and pulls the insect back into its
mouth. Then the frog snaps its mouthmouth. Then the frog snaps its mouth
shut and swallowsshut and swallows..

Frogs have twoFrogs have two
types of teethtypes of teeth
that hold on tothat hold on to
prey. A row ofprey. A row of
maxillary teethmaxillary teeth
line the perimeterline the perimeter
of the upper jaw.of the upper jaw.
Two patches ofTwo patches of
vomerine teethvomerine teeth
project fromproject from
bones in the roofbones in the roof
of the mouthof the mouth..

 Sometimes the frogSometimes the frog
blinks, pulls its eyesblinks, pulls its eyes
inward, and presses theminward, and presses them
against the roof of itsagainst the roof of its
mouth. This action helpsmouth. This action helps
push the food down itspush the food down its
throatthroat
 Digestion in frogs takesDigestion in frogs takes
place in the alimentaryplace in the alimentary
canal, which includes thecanal, which includes the
esophagus, stomach, smallesophagus, stomach, small
intestine, large intestine,intestine, large intestine,
and cloacaand cloaca

Circulatory SystemCirculatory System
An adaptation to theAn adaptation to the
greater oxygen needs ofgreater oxygen needs of
land animals is a moreland animals is a more
efficient circulatoryefficient circulatory
system than the fish'ssystem than the fish's
two-chambered heart.two-chambered heart.
The amphibian's three-The amphibian's three-
chambered heartchambered heart
partially mixespartially mixes
oxygenated withoxygenated with
deoxygenated blood anddeoxygenated blood and
pumps the bloodpumps the blood
throughout the body atthroughout the body at
higher pressure thanhigher pressure than
does the fish's heartdoes the fish's heart

The left atriumThe left atrium
receives oxygenatedreceives oxygenated
blood from the lungs,blood from the lungs,
and the right atriumand the right atrium
receives deoxygenatedreceives deoxygenated
blood from the body.blood from the body.
Both the atria emptyBoth the atria empty
into the ventricle, theinto the ventricle, the
main pumping chambermain pumping chamber
of the heart.of the heart.
In the ventricleIn the ventricle
oxygenated andoxygenated and
deoxygenated blooddeoxygenated blood
mix partially and aremix partially and are
pumped to the lungspumped to the lungs
and the rest of theand the rest of the
bodybody..
Blood to
body
Deoxygenated
blood
from body
R
Oxygenated
blood from
lungs

From the right atriumFrom the right atrium
the blood enters thethe blood enters the
single ventricle. Thesingle ventricle. The
ventricle thenventricle then
contracts, pumpingcontracts, pumping
some blood to thesome blood to the
lungs to receivelungs to receive
oxygen and some tooxygen and some to
the rest of the body.the rest of the body.
The blood going to theThe blood going to the
body leaves thebody leaves the
ventricle through theventricle through the
conus arteriosus, aconus arteriosus, a
large vessel that lieslarge vessel that lies
against the front sideagainst the front side
of the heartof the heart Copyright CmassengaleCopyright Cmassengale

This vessel divides into a right andThis vessel divides into a right and
a left truncus arteriosus, whicha left truncus arteriosus, which
immediately branch again into threeimmediately branch again into three
arches that carry blood to variousarches that carry blood to various
parts of the body.parts of the body.
Deoxygenated blood travels in veinsDeoxygenated blood travels in veins
back to the right atrium from theback to the right atrium from the
various regions of the body.various regions of the body.
Oxygenated blood returns from theOxygenated blood returns from the
lungs to the left atrium via thelungs to the left atrium via the
pulmonary veinspulmonary veinsCopyright CmassengaleCopyright Cmassengale

Respiratory SystemRespiratory System
Tadpoles respire, orTadpoles respire, or
exchange carbon dioxide andexchange carbon dioxide and
oxygen, through gillsoxygen, through gills

Adult frogs lose the gills but canAdult frogs lose the gills but can
respire in three ways: throughrespire in three ways: through
the lungs, through the skin, andthe lungs, through the skin, and
through the mouth.through the mouth.
Respiration through the lungs isRespiration through the lungs is
called pulmonary respiration.called pulmonary respiration.
A frog breathes by changing theA frog breathes by changing the
volume and pressure of air in itsvolume and pressure of air in its
mouth while either opening ormouth while either opening or
closing its nostrilsclosing its nostrilsCopyright CmassengaleCopyright Cmassengale

 Air moves from the throat to theAir moves from the throat to the
lungs through a slit-like passagelungs through a slit-like passage
called the glottis.called the glottis.
 Because the frog's lungs are small,Because the frog's lungs are small,
cutaneous respiration, or respirationcutaneous respiration, or respiration
through the skin in both air andthrough the skin in both air and
water, is very important, especiallywater, is very important, especially
during estivation or hibernation.during estivation or hibernation.
 Oxygen can diffuse across theOxygen can diffuse across the
lining of the mouth and into thelining of the mouth and into the
blood.blood.
 Frogs use mouth breathing for onlyFrogs use mouth breathing for only
a relatively small amount of theira relatively small amount of their
respirationrespiration..

Excretory SystemExcretory System
Urine and wastes from the digestiveUrine and wastes from the digestive
system are eliminated through the anus.system are eliminated through the anus.
When a frog is in water, its permeableWhen a frog is in water, its permeable
skin allows the water to enter its body.skin allows the water to enter its body.
Frogs thatFrogs that livelive primarily in water ridprimarily in water rid
themselves of excess water bythemselves of excess water by
excreting a large volume of very diluteexcreting a large volume of very dilute
urine.urine.
 Frogs that live mainly on land conserveFrogs that live mainly on land conserve
water by producing a small volume ofwater by producing a small volume of
more concentrated urine.more concentrated urine.Copyright CmassengaleCopyright Cmassengale

Excretory SystemExcretory System
 Amphibians eliminate two primary types of metabolicAmphibians eliminate two primary types of metabolic
waste products—carbon dioxide from respiration andwaste products—carbon dioxide from respiration and
waste compounds from the breakdown of foodswaste compounds from the breakdown of foods..
 Are the primary excretory organs and lie on eitherAre the primary excretory organs and lie on either
side of the spine against the dorsal body wall. Theside of the spine against the dorsal body wall. The
kidneys filter nitrogenous wastes from the bloodkidneys filter nitrogenous wastes from the blood

The Nervous SystemThe Nervous System
The frog brain is moreThe frog brain is more
complex than the fish brain,complex than the fish brain,
enabling the frog to contendenabling the frog to contend
with a more variedwith a more varied
environment.environment.
The optic lobes, whichThe optic lobes, which
control vision, lie behind thecontrol vision, lie behind the
cerebrum.cerebrum.
 The cerebellum, a smallThe cerebellum, a small
band of tissue lying at rightband of tissue lying at right
angles to the long axis ofangles to the long axis of
the brain, is the center ofthe brain, is the center of
balance and coordinationbalance and coordination..Copyright CmassengaleCopyright Cmassengale

Nervous SystemNervous System
The medulla oblongata lies at the backThe medulla oblongata lies at the back
of the brain and joins the spinal cord.of the brain and joins the spinal cord.
It controls organ functions.It controls organ functions.
 Ten pairs of cranial nerves extend outTen pairs of cranial nerves extend out
directly from the brain.directly from the brain.
The spinal cord transmits signals fromThe spinal cord transmits signals from
all parts of the body to the brain andall parts of the body to the brain and
from the brain back to the body.from the brain back to the body.
The spinal nerves branch from theThe spinal nerves branch from the
spinal cord to various parts of thespinal cord to various parts of the
body.body.

Reproductive SystemReproductive System
 Both male and female frogsBoth male and female frogs
have internal sex organshave internal sex organs
 The male frog's forelegThe male frog's foreleg
muscles and first fingers swellmuscles and first fingers swell
 These swellings help the maleThese swellings help the male
maintain his grasp on the femalemaintain his grasp on the female
 The reproductive system of theThe reproductive system of the
male frog includes two bean-male frog includes two bean-
shaped creamy white orshaped creamy white or
yellowish testes located nearyellowish testes located near
the kidneysthe kidneys
 Sperm cells develop in theSperm cells develop in the
testes and pass through tubestestes and pass through tubes
to the kidneys and urinary ductsto the kidneys and urinary ducts
Male System

Female frogs a pair ofFemale frogs a pair of
large, lobed ovarieslarge, lobed ovaries
containing thousands ofcontaining thousands of
tiny immature eggs lie neartiny immature eggs lie near
the kidneysthe kidneys
During the breeding seasonDuring the breeding season
eggs enlarge, mature, andeggs enlarge, mature, and
burst through the thinburst through the thin
ovarian walls into the bodyovarian walls into the body
cavity.cavity.
They remain in structuresThey remain in structures
called ovisacs untilcalled ovisacs until
ovulation is complete andovulation is complete and
then leave the bodythen leave the body
through the cloacaethrough the cloacae
opening.opening. Female SystemCopyright CmassengaleCopyright Cmassengale

 The vast majority of eggsThe vast majority of eggs
and tadpoles are eaten byand tadpoles are eaten by
predators such as fish,predators such as fish,
birds, snakes, and turtles.birds, snakes, and turtles.
Some species of frogsSome species of frogs
havehave
 The vast majority of eggsThe vast majority of eggs
and tadpoles are eaten byand tadpoles are eaten by
predators such as fish,predators such as fish,
birds, snakes, and turtlesbirds, snakes, and turtles.. Amplexus

MetamorphosisMetamorphosis
Newly hatched tadpoles live offNewly hatched tadpoles live off
yolk stored in their bodies. Theyyolk stored in their bodies. They
gradually grow larger and developgradually grow larger and develop
three pairs of gills.three pairs of gills.
Tadpoles have a two-chamberedTadpoles have a two-chambered
heart. Tadpoles can also regenerateheart. Tadpoles can also regenerate
injured or lost body parts such as ainjured or lost body parts such as a
leg or tail.leg or tail.
Legs grow from the body, and theLegs grow from the body, and the
tail disappears.tail disappears.

MetamorphosisMetamorphosis
 The mouth broadens, developingThe mouth broadens, developing
teeth and jaws. A sacliketeeth and jaws. A saclike
bladder in the throat dividesbladder in the throat divides
into two sacs that becomeinto two sacs that become
lungs. The heart develops alungs. The heart develops a
third chamber.third chamber.
 A hormone called thyroxinA hormone called thyroxin
circulates throughout thecirculates throughout the
bloodstream and stimulatesbloodstream and stimulates
metamorphosis.metamorphosis.
 The cells of the tadpole areThe cells of the tadpole are
genetically programmed togenetically programmed to
respond to thyroxin at therespond to thyroxin at the
appropriate stage ofappropriate stage of
development.development. Copyright CmassengaleCopyright Cmassengale

Amphibians

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