1. First Tetrapods on Land
Amphibians
First Tetrapods on Land

2. Class: Amphibia First truly tetrapod vertebrate Ectothermic
All amphibians have bony skeletons
Most have 4 limbs, except Caecilians (limbless)
Many have webbed feet
Typically the glandular skin is smooth, moist, and lacks scales
Metamorphose from juvenile water breathing to adult air breathing
Ecological indicators

3. Order Anura (Salientia): Frogs and Toads
Order Caudata (Urodela): Salamanders, Newts, Waterdogs, Mudpuppies, Sirens, and Amphiuma
Order Gymnophiona (Apoda): Caecilians

4. Class: Amphibia
Gas exchange occurs through lungs, gills, and/or the skin
Some salamanders have no lungs (secondarily lost)
Adults have double circulation
Both a pulmonary and a systemic circuit
Heart has three chambers
Two atria and one ventricle
Some mixing of oxygenated and deoxygenated blood occurs in ventricle

5. Anamniotic egg Jellylike Small-sized unshelled; must develop in water
Jellylike
unshelled; must develop in water
Small-sized
lack large membranes to nourish embryo and store waste
Amphibian egg mass

6. Amphibian development
Newt
Controlled by the hormone thyroxin