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Amphibians
Chapter 40
Origins & Evolution of
Amphibians
Section 40.1
Adaptation to land
• Amphibian means “double life”
• Came out of the water to escape
predation & competition for food
– Need a strong bony endoskeleton to deal
with force of gravity
Characteristics of early
amphibians
• Oldest amphibian fossil is 370 myo
• Evolved from lobe-finned fish
– Four limbs homologous to pectoral &
pelvic fins of fish
– Similar skull & vertebrae
• some had gills and lungs
• More toes than modern
amphibians
Diversification of amphibians
• Two main evolutionary lines
1. Modern amphibians
2. Ancestor of reptiles
• 4,500 species in 3 orders
1. Order Anura
2. Order Caudata
3. Order Gymnophiona
Modern amphibians
• Metamorphosis
• Moist, thin skin with no scales
• Feet lacking claws & often
webbed
• Use skin, gills, & lungs to
breathe
• Eggs lack membrane or shells
• Eggs laid in water
• Fertilization externally
Order Anura
• Meaning “tail-less”
• Examples: frogs & toads
– “toad” = rough, bumpy skin
– “frog” = smooth, moist skin
• Adaptations for jumping
• Tadpole: swimming larvae
• Carnivores
Order Caudata
• Example: salamanders & newts
• Elongated bodies with moist skin and
long tails
• Live in moist places
• Carnivores
Order Gymnophiona
• Example: caecilian
• Legless & resemble small snakes
• Very small eyes, often blind
• Carnivores
3 Order Note Cards!
• Front Side = Order name & picture
• Back Side =
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Anura
Caudata
Gymnophiona
example organisms
Location of animal on Earth
Habitat/environment
Adaptations for life/ key characteristics
Fun fact!
Characteristics of
Amphibians
Section 40.2
External covering
• Skin = respiration & protection
• Mucous glands: supply lubricant to
keep skin moist & poison for protection
Poison dart frogs
Internal anatomy
• Strong bony skeleton
– Needed for life on land (larger animals)
– Pectoral & pelvic girdles help support
• More developed internal anatomy
– Closer to humans!
– video
Male internal anatomy
a. Large intestine.
b. Small intestine.
1. Lung lobes.
2. Heart.
3. Liver lobes.
4. Gall bladder.
5. Stomach.
6. Small intestine.
7. Testis.
8. Fat body.
9. Urinary bladder.
Female internal anatomy
1. Liver lobes.
2. Heart.
3. Ovary with eggs.
4. Gall bladder.
5. Small intestine.
6. Stomach.
7. Oviduct.
Heart & circulatory system
• Two separate loops
1. Pulmonary circulation: blood from heart
to lungs & back to heart
2. Systemic circulation: blood from heart to
muscles & organs then back to the heart
Three chambered heart
1. Right atrium: where (deoxygenated)
blood enters the heart from the body
2. Left atrium: where oxygenated blood
enters from the lungs
3. Ventricle: main pumping chamber
1.
2.
3.
Path of blood
• Right atrium  ventricle  lungs (to
pick up oxygen) left atrium 
ventricle  rest of body (to drop off
oxygen)
Respiration
• Larvae respire via gills and skin
• Adults respire via lungs and skin
– Pulmonary respiration: through lungs
– Cutaneous respiration: through skin
Digestive system
• All adults are carnivores
• New terms:
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Pyloric sphincter:
Duodenum:
Ileum:
Mesentery:
Cloaca:
Vent:
Excretory system
• Two kidneys that filter
nitrogenous wastes from
the blood
• Urine flow:
– Kidneys  urinary ducts 
urinary bladder  cloaca
Reproductive system
• Males:
– Testes (sperm made here)  sperm ducts
 cloaca
• Females:
– Ovaries (eggs made here)  oviducts 
uteri  cloaca
Nervous system
• Brain:
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Olfactory lobes
Cerebrum
Optic lobes
Cerebellum
Medulla oblongada
• Nerves
– 10 pair cranial nerves
– Spinal cord
– Spinal nerves
Sense organs
• light travels through nictitating
membrane
– transparent movable membrane covering
the eyes while underwater
• Sound: travels through tympanic
membrane (eardrum)  columella
(small bone) inner ear (embedded in
skull)
Reproduction of Amphibians
Section 40.3
Life cycle
Courtship & fertilization
• Males croak to females in spring
• Amplexus: male embrace of female
during mating
– May last for days!
– Once female releases eggs, male
releases sperm  external fertilization
Metamorphosis
• Tadpole  frog
The real one
Parental care
• Males often remain with eggs
for protection
• Example: Darwin’s frog puts
eggs in his vocal sac where
they hatch, go through
metamorphosis, and emerge
in the adults form