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

LOBE-FINNED FISH www.abdn.ac.uk/.../coelacanth/coelacanth.jpg

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

www.estrellamountain.edu/.../comparison.gif

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