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Early Tetrapods and Modern Amphibians

Early Tetrapods and Modern Amphibians. Early tetrapods had to accommodate to the following differences when adapting to land 1) prevention of dessication 2) oxygen in a different medium (air) 3) density (gravity) 4) temperature fluctuations 5) habitat diversity.

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Early Tetrapods and Modern Amphibians

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  1. Early Tetrapods and Modern Amphibians • Early tetrapods had to accommodate to the following differences when adapting to land • 1) prevention of dessication • 2) oxygen in a different medium (air) • 3) density (gravity) • 4) temperature fluctuations • 5) habitat diversity

  2. Major Developments For Movement To Land – Lungs and Limbs • Vascular plants, pulmonate snails, and insects have already adapted to land • Involves lobe-finned ancestor • Devonian period (400 million years ago); mild temps with alternating droughts and floods • Surviving fishes in shallow water 1) developed lungs from out growth of pharynx • 2) increased blood flow by developing pulmonary circulation (tetrapod double circulation with systemic and pulmonary circuits • 3) developed four weight bearing limbs from stout, fleshy appendages of lobed fins • Devonian followed by Carboniferous period which was a warm and moist climate • Amphibians went through much adaptive radiation feeding on abundant insects

  3. Figure 17_01

  4. Figure 17_03

  5. Modern Amphibians • Descended from lissamphibians; diverged into the 3 groups of caecilians, salamanders, and frogs/toads • Possess: • 1) 4 digits on fore-limbs, 5 on rear; caecilians are limbless • 2) often with webbed feet with no nails or claws • Ectothermic • Smooth, moist, glandular skin • Respiration by skin, lungs, or gills • Double circulation • Gelatinous eggs

  6. Caecilians (Order Gymnophiona; aka Apoda) • Limbless and elongate (snake-like) • Burrow underground; found in tropical rainforests

  7. Salamanders (Order Urodela; aka Caudata) • Tailed with 4-legged body plan of ancestral forms • Internal fertilization; female accepts spermatophore from male • Eggs often found in water • Some species exhibit paedomorphosis; the retention of larval characteristics while reaching sexual maturity • 1) remain aquatic • 2) retention of gills

  8. Figure 17_10

  9. Frogs and Toads (Order Anura; aka Salientia) • Largest group of amphibians • Specialized legs for jumping with webbed feet • No tail, but possess during larval stages • Undergo major metamorphosis from tadpole to adult • Males court females; undergo copulatory embrace called amplexus • Many unique reproductive strategies • Toads are stockier, with thicker skin (“warts”), often with poison glands, and are more terrestrial

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