Fact of the week: Which came first?

I was reading about eggs recently when I discovered that the information I had about how birds hatched was wrong.

So back to the basics. Bady birds use their egg tooth to make a hole in the eggshell. They then use the egg tooth like a diamond cutter to cut a 360-degree line inside the shell. Then they use their egg muscle to force off the top of the shell. The fallacy was that birds dig their way out of the egg. The first hole is meant for breathing. 

Then I discovered that most animal that is hatched from a calcium eggshell has an egg tooth. Reptiles have it (Some reptiles have a real tooth that falls off shortly after birth.). Monotremes have it. The egg tooth in monotremes also means that the mother has to produce out of openings in the skin to prevent being bitten.  

I also found out that crocodile mothers also have to play midwife if their children have a problem breaking out of the egg. Then the babies get a year of parental protection and supervision.