Early Tetrapods and Modern Early Tetrapods and Modern AmphibiansAmphibians

Early tetrapods had to Early tetrapods had to accommodate to the following accommodate to the following differences when adapting to landdifferences when adapting to land

1) prevention of dessication1) prevention of dessication 2) oxygen in a different medium (air)2) oxygen in a different medium (air) 3) density (gravity)3) density (gravity) 4) temperature fluctuations4) temperature fluctuations 5) habitat diversity5) habitat diversity

Major Developments For Movement To Major Developments For Movement To Land – Lungs and LimbsLand – Lungs and Limbs

Vascular plants, pulmonate snails, and insects have already Vascular plants, pulmonate snails, and insects have already adapted to landadapted to land

Involves lobe-finned ancestorInvolves lobe-finned ancestor Devonian period (400 million years ago); mild temps with Devonian period (400 million years ago); mild temps with

alternating droughts and floodsalternating droughts and floods Surviving fishes in shallow water 1) developed lungs from out Surviving fishes in shallow water 1) developed lungs from out

growth of pharynx growth of pharynx 2) increased blood flow by developing pulmonary circulation 2) increased blood flow by developing pulmonary circulation

(tetrapod (tetrapod double circulationdouble circulation with systemic and pulmonary circuits with systemic and pulmonary circuits 3) developed four weight bearing limbs from stout, fleshy 3) developed four weight bearing limbs from stout, fleshy

appendages of lobed finsappendages of lobed fins

Devonian followed by Carboniferous period which was a warm Devonian followed by Carboniferous period which was a warm and moist climateand moist climate

Amphibians went through much adaptive radiation feeding on Amphibians went through much adaptive radiation feeding on abundant insectsabundant insects

Figure 17_01Figure 17_01

Figure 17_03Figure 17_03

Modern AmphibiansModern Amphibians

Descended from lissamphibians; diverged into Descended from lissamphibians; diverged into the 3 groups of caecilians, salamanders, and the 3 groups of caecilians, salamanders, and frogs/toadsfrogs/toads

Possess:Possess: 1) 4 digits on fore-limbs, 5 on rear; caecilians 1) 4 digits on fore-limbs, 5 on rear; caecilians

are limblessare limbless 2) often with webbed feet with no nails or claws2) often with webbed feet with no nails or claws EctothermicEctothermic Smooth, moist, glandular skinSmooth, moist, glandular skin Respiration by skin, lungs, or gillsRespiration by skin, lungs, or gills Double circulationDouble circulation Gelatinous eggsGelatinous eggs

Caecilians (Order Gymnophiona; aka Caecilians (Order Gymnophiona; aka Apoda)Apoda)

Limbless and elongate (snake-like)Limbless and elongate (snake-like) Burrow underground; found in tropical Burrow underground; found in tropical

rainforestsrainforests

Salamanders (Order Urodela; aka Salamanders (Order Urodela; aka Caudata)Caudata)

Tailed with 4-legged body plan of ancestral formsTailed with 4-legged body plan of ancestral forms Internal fertilization; female accepts spermatophore Internal fertilization; female accepts spermatophore

from malefrom male Eggs often found in waterEggs often found in water

Some species exhibit Some species exhibit paedomorphosis;paedomorphosis; the retention of the retention of larval characteristics while reaching sexual maturitylarval characteristics while reaching sexual maturity

1) remain aquatic1) remain aquatic 2) retention of gills2) retention of gills

Figure 17_10Figure 17_10

Frogs and Toads (Order Anura; aka Frogs and Toads (Order Anura; aka Salientia)Salientia)

Largest group of amphibiansLargest group of amphibians Specialized legs for jumping with webbed feetSpecialized legs for jumping with webbed feet No tail, but possess during larval stagesNo tail, but possess during larval stages Undergo major metamorphosis from tadpole to adultUndergo major metamorphosis from tadpole to adult Males court females; undergo copulatory embrace Males court females; undergo copulatory embrace

called called amplexusamplexus Many unique reproductive strategiesMany unique reproductive strategies

Toads are stockier, with thicker skin (“warts”), often Toads are stockier, with thicker skin (“warts”), often with poison glands, and are more terrestrialwith poison glands, and are more terrestrial