U NIT Q UESTIONS 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.
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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
By: Debra Cunningham
EARLY TETRAPODS AND MODERN AMPHIBIANS
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
ADAPTATIONS FOR LIFE ON LAND
SENSORY DEVELOPMENT SKELETAL STRUCTURE
Special sense priority shift
Foreshortening skull
Lengthened snout
Advanced ear structure (tympanic membranes)
Olfactory epithelium to detect airborne odors
Skeletal strengthening
Stronger backbone
Strengthened shoulder and hip girdle; tetrapod leg
Protective rib cage
Muscles to support body in air and elevate head
MODERN AMPHIBIANSwww.caf.wvu.edu/~rwhitmor/wman224/.../Modern
%20amphibians.pdf
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
FROGS AND TOADS•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
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
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