Were you aware that embryonic turtles are able to communicate with one another when getting ready to hatch? Even if they are from entirely different species, these embryos have found a method to form a "group chat" in order to synchronize their development and therefore extend their chances of survival when running together in mass to the ocean from the nest. For that, the most mature embryos leave more oxygen to the ones that are behind, so eventually they are ready to hatch at the same time.