I think the chicken. Only it didn't start as a chicken. It gradually developed into a chicken from someone other species.
Two similarly exisiting species that may have not necessarily been egg-layers, met by chance and 'created' offspring that happened to develop in egg form.
Or perhaps the actually shell part developed later as a protective mechanism to keep the egg intact. Perhaps chickens then, predate eggs. The shell part came later.
I have no academic knowledge to support this - I know only that when creating other things (music, art) that incredible things can happen purely by chance or accident.
Sometimes, two different pieces of music can be left playing together (I might leave a reference CD on with a current track I am working on) and bang - a violin and a flute on both combine with such perfection that they must then be married together.
In fact, what if chickens developed from water creatures over a long period of time? Perhaps in water there would be no need for a shell - like frogspawn; which has a very 'filmy' outer case, like that of the inside of an egg.
''Or perhaps the actually shell part developed later as a protective mechanism to keep the egg intact. Perhaps chickens then, predate eggs. The shell part came later.''
Yes! What if chicken didn't lay eggs to begin with? The shell just developed cos you know...wonder if humans will come out in shells at one point - erm, are we still evolving?
So the question Yum is, where did dino egg come from?
What if the egg was an aborted mutant pre-term defect that came from another species. It survived, just happened to contain twins and little Adam chicken and Eve chicken spawned what for us, would become an entire lifetime of delicious omelettes?