Egg burier animals question

Hi.I have a question regarding animals like the Maleo (Maleo - Wikipedia) that bury their eggs deep in the ground, and how the young birds are able work their own way up through the sand.How did that incubation method probably evolved? If the young birds didn't had the ability to dig up then they would have becomed extinct as the mother burried into the ground; but the ability to dig up would be useless otherwise.Whats the current scientific explanation for the evolution of animals that bury their eggs in the ground?ThanksEdited by Garabato, : No reason given.Edited by Garabato, : Spelling mistakes

Thanks for the suggestion AdminNosy. I probably failed to make myself clear. My question was not regarding how two interdependent features could have evolved as my first post made it sound, I ment to ask the specific question of how did the Maleo's egg burial feature evolved.Thinking gradually as you said I could especulate something. Birds already have to get trought a strenuous process to extract themselves from an unburied egg. One could imagine the early stages of the evolution of egg burying involving a very shallow layer of dirt that way, so the diference wouldn't be so sudden.Now since there are evolutionary advantages for deeper burial (I think). Then there is selective pressure for greater depth of burial. So after many generations of slightly increase of burial depth, the individuals who had slightly increase of physical activity to reach the surface would have a higher chance of surviving, thus having a higher chance to leave offspring.I dont know if it goes like that, my understanding of the evolution model is pretty limited to be honest. But the thread was regarding the current scientific explanation of this feature from an evolutionary perspective, hope that clears thing up.Thanks