Some characteristics 1. Skeleton ossified, ribs with sternum, sternum absent in snakes. Respiration by lungs no gills three chambered heart four in crocodiles 3. Metanephric kidneys , Uric acid main nitrogenous waste, 4. Ectothermic, due to ectothermy, reptiles can survive on a much lower caloric intake than mammals of comparable size 5.
Reptiles have a copulatory organ permiting internal fertilization, necessary for a shelled egg.
Epidermal covering of feathers 2. Skeleton ossified with air cavities 3.