Don_DickleHas society or scientists ever solved definitively the Chicken and the Egg theory? Or is it just like a whose on first thing?
JohnnyEnzymeYes, based on a quick lookup, it appears that the first (internal) egg was produced by sexually-reproducing animals over 600m yrs ago. Later, shelled (external) eggs seem to have appeared about ~315yrs ago.
So basically, the egg was a very ancient, fundamental innovation in complex life that appeared well before galliforms (chickens and relatives) did, ~85m yrs ago.