Reptiles & Amphibians
Amphibians were the first tetrapods to make land their home. They used lungs to breathe air, although they primarily absorbed gases through their skin. They need water to breed since their eggs are fertilized externally and do not have a reliably supply of water inside of them. Amphibians also has the first true vocalizations. Most of their adult terrestrial forms are foul tasting or have a poisonous mucus.
Reptiles have scales made out of tough keratin and are ectothermic, meaning the environment determines their body temperatures. They were the first to gain a three chambered heart and have much better developed lungs than those of amphibians. Both reptiles and birds are the only groups of animals to have nucleated red blood cells. Reptiles can reproduce without a reliable water source because their eggs have a hardened shell with an amniotic cavity that holds fluid for the embryo and a chorion which contains gases for the embryo.
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