Why is the amniotic egg so important ?

Why is the amniotic egg so important?

The reason we consider amniotic eggs so important is that we're descended from them (the same reason we tend to think the evolution of internal skeletons is more important than the evolution of exoskeletons or shells, even though exoskeletons and shells are far more widespread). Amniotic eggs did make it much easier for animals to reproduce on land away from bodies of water. And amniotic eggs can be much bigger (compare the size of fish or frog eggs to hen's eggs, let alone ostrich eggs). This allowed animals' young to be larger and more developed when they hatched (two reasons they can be bigger are waste sequestration and improved respiration). 

A clutch is the bunch of eggs which a bird brings up together. They're laid on consecutive days or with a day or two between each egg. 

With a two chambered heart, blood passes through the lungs (gills, actually) before it goes to the rest of the body and returns to the heart. The blood has to pass through tiny blood vessels in the gills to pick up oxygen, so you get a large drop in blood pressure before the blood gets to the rest of the body. But all of the blood is fully oxygenated. 

A three chambered heart separates blood going to the heart from blood going to the rest of the body - sort of. It does enable blood going to the body to be at full pressure, but the blood going to the lungs and the blood going to the body both get mixed together and pumped from the same ventricle, so the blood circulating in the body is a mix of oxygenated and depleted blood. 

A four chambered heart completely separates the blood to the lungs and the blood to the body. Blood goes to the lungs first, back to the heart, and then to the rest of the body. All the blood going to the body is fully oxygenated.