General Discussion

at no point would we be able to draw a line saying "On this side are individuals that are chickens, and on this side are individuals that are not chickens." At every juncture in the chicken's ancestry, every offspring would have been the same sort of creature as its parents, and of its own offspring.

Now we can find creatures that are ancestral to chickens that are themselves not chickens. But we would be unable to define the exact point that the "change" happened, unless the condition of chicken-hood is based entirely on a single particular feature that arose from a single particular mutation - and while I'm no expert on chicken biology, I don't think they're one of the handful of species that work like that.

And the really weird thing is?

These primeval almost-chickens... probably looked more like a chicken, than a lot of modern chickens do!