Depends on your definition of "chicken egg". Language is defined by the way people use it and nobody (other than perhaps a few people in this thread) has ever bothered defining what a chiclen egg is: Is it an egg laid by a chicken or is it an egg that contains a chicken

When you go to the supermarket you call that a chicken egg because it was laid by a chicken, even if the egg is incapable of ever containing a chicken (at least from what I know you can't grow chickens from supermarket eggs) So arguably that means eggs laid by chickens are chicken eggs. But nobody has ever had to define whether an egg containing a chicken is also a chicken egg, even if the egg was not laid by a chicken. So if you don't define an egg laid by a proto-chicken to be a chicken egg then you would say that the chicken came before the egg.