Transcript Slide 1

HOW DID AMPHIBIANS, SUCH AS
FROGS, TRADE THEIR TAILS
FOR LEGS?
UNIT QUESTIONS
1.
How did the tetrapod leg evolve?
2.
Why did early animals move from water to
land?
3.
How did amphibians transition from life in
water to life on land?
4.
What are the three major groups of modern
amphibians
EARLY TETRAPODS AND MODERN AMPHIBIANS
By: Debra Cunningham
EARLY TETRAPODS
 Terrestrial vertebrates adapted
 Tetrapod leg evolved
 Modern amphibians transitioned
 Caecilians
 Salamanders
 Frogs and toads
ORIGIN
OF
TERRESTRIAL VERTEBRATES
 The Devonian period
 400 million years ago
 time of mild temperatures
 alternating droughts and floods
 Lungs and limbs evolved for terrestrial life
 Unstable freshwater environment
 Pools and streams evaporated
 Foul water resulted
 Lobe-finned and lungfish evolved into modern
amphibians
EVOLUTION
OF
TETRAPOD LEG
 Lobe-finned fish fins
 Paddle-like fins
 Paired muscular fins
 Anterior fin - humerus
 Forearm bones - radius and ulnar
 Bony elements - wrist bones
LOBE-FINNED FISH
www.abdn.ac.uk/.../coelacanth/coelacanth.jpg
ADAPTATIONS FOR LIFE ON LAND
SENSORY DEVELOPMENT
SKELETAL STRUCTURE
 Special sense priority shift
 Skeletal strengthening
 Foreshortening skull
 Stronger backbone
 Lengthened snout
 Strengthened shoulder and
 Advanced ear structure
(tympanic membranes)
 Olfactory epithelium to
detect airborne odors
hip girdle; tetrapod leg
 Protective rib cage
 Muscles to support body in air
and elevate head
www.estrellamountain.edu/.../comparison.gif
MODERN AMPHIBIANS
• gymnos +
opineos =
“naked of a
snake”
• ≈ 160 species
• South America
principal home
• Caudata
• caudatus =
having a tail
• ≈ 360 species
• Found in most
northern
temperate
regions of the
world
FROGS AND TOADS
• Gymnophiona
SALAMANDERS
CAECILIANS
www.caf.wvu.edu/~rwhitmor/wman224/.../Modern%20amphibians.pdf
• Anura
• an + oura =
without a tail
• ≈ 3450 species
• Found near
water, swamps
or on damp
forest floors
Amphibian Breeding Habits
▪ Caecilians:
• Internal fertilization
• Deposit eggs in moist soil
▪ Salamanders:
• Internal fertilization
• Lay eggs in stringy masses, clusters in water
▪ Frogs and Toads:
• External fertilization
• Lay eggs in masses anchored to vegetation
CAECILIANS
• Elongated body, limbless
• Small scales on skin
• Many vertebrae (95-285)
• Small eyes (adults blind)
• Sensory tentacles on snout
• Pantropical
SALAMANDERS
Typically small
• Limbs set at right
angles to body
• Forelimbs & hindlimbs
are equal in size
• Vertebrae (10-60)
• Breathe through skin
• Ectothermic;
predominantly holarctic
FROGS
•Typical tetrapod
pattern of bones and
muscles
• Shortened body-only
nine (9) trunk vertebrae
• Three main joints in
each limb
• Light-weight skull
with flattened profile
• Tail and gills resorbed
• Ectothermic
AND
TOADS
LIFE CYCLE OF A FROG
 http://www.scienceclarified.com/Al-As/Amphibians.html
CONCLUSION
 Frogs traded their tails for legs
 Modern amphibians evolved from
lobe-finned fish
 Modern amphibians transitioned from
water to land
REFERENCES
Hickman, Jr. C.P., Roberts, L.S., & Larson, A. (2001). Integrated Principles of Zoology, ed 11. McGraw-Hill:
Boston, 538-558.
Color illustrations and pictures from:




http://www.scienceclarified.com/Al-As/Amphibians.html
www.abdn.ac.uk/.../coelacanth/index.html
www.caf.wvu.edu/~rwhitmor/wman224/.../Modern%20amphibians.pdf
www.estrellamountain.edu/.../comparison.gif