Their eggs have no egg shells, so the sperm can swim through the water to the eggs, and the embryos must develop in water. Reptiles have scales and are dry to the touch. Their eggs have leathery shells. Some dinosaurs may have been endothermic. It is thought that birds are descended from dinosaurs, as evidenced, in part, by the scales on their feet.
Birds bones are light weight for flight.
Birds have shelled eggs and so must have internal fertilization the egg muct be fertilized before the hen s reproductive tract secretes an eggshell. Generally, mating is accompanied by an elaborate courtship ritual. Mammals have a diaphragm to aid in respiration. They are endothermic. Most mammals bear live young.