There were eggs long before there were anything like a bird or a chicken.

But if you're on the strict interpretation, the change was so gradual over so many generations it's hard if not impossible to detect. Even when it speciates (becomes unable to produce viable offspring after mating) is hard to tell. There was like likely a long stretch of many generations where sometimes it worked, sometimes it didn't.

TL:DR; How long is a piece of string?

edit: Variation of the same question: Were there radio waves before there radios? Jupiter and thunderstorms produce them, but we had no way of knowing so to us they did not exist.