Amphibians were thee earliest tetrapods. Skin is covered with scales composed of protein called keratin. There is no larval stage. They have amniotic eggs. Current thinking holds that birds evolved for an ancestral bi-pedal dinosaur.
Mammals are a largely terrestrial group with hair and milk producing glands.
They are endotherms. It's believed that mammals evolved form a small reptilian ancester before the age of the dinosaurs. But they showed a dramatic speciation after the dinosaurs became extinct. Restricted to the antipodes. These include the duck-billed platypus, and several species of spiny anteater.