Chicken egg looks like dinosaur egg!?

[Gingersprite]

I uploaded a photo of an egg with major cracks around the middle, one of my girls has laid 3 like this. I have looked up odd eggs but this doesn't obviouly match any of the ones I found. I am concerned that I should figure out who is laying them and do something? They get plenty of calcium in oyster shells, and varied diet of pellets and corn and leftovers from us. Lots of veggies etc. All appear healthy except for bare butts on 4 (another issue).
Any clues? Do I need to worry for her? Thanks in advance!

 

[sonew123]

sometimes this just happens as thier plumbing needs to be worked out Unless she gets eggbound I would nto worry at all

 

[Gingersprite]

Thank you, and how would I recognize if she got egg bound; I haven't had this happen yet, fortunately!