At one point a chicken's ancestor (let's call it chocken) would lay an egg which contains the first chicken. Now would you call that a "chocken's egg" or chickens egg?
If it's a chocken's egg, the the chicken came first. If it's a chicken's egg, the egg came first.
I personally think it's a chocken's egg so I say the chicken came first but it's more of a philosophical question than a scientific one.
chicken 🐔