I am fairly certain this came from one of my young speckled sussex birds. But I can't be positive. This is a large fowl egg, I don't own any bantam chickens. I'm guessing this is one of the first eggs she has ever laid. The quarter is for size reference.
I have three silver lakenvelders and they lay eggs that are long and pointy with that wrinkled top. I like yours, it sort of reminds me of a potato or something.
I don't have a picture, but one of my girls lays an egg that is flat on two sides. It won't roll away if you set it on the counter. It happens every time. I'm not sure who is laying it as I have 6 birds that lay brown eggs.
My little golden campine hen laid a "Snowman" egg. It looks big in the picture but it was really the size of an 'egg fart' as you can see in the picture using the quarter to show the size of the egg. The 3rd picture shows how the 2 sections were joined in the back of the egg.
The little 'snowman' even came with a 'face' already on it and not only that....one of the 'eyes' looks like a sillouette (sp?) of a chicken!!! How talented is THAT?!