i didn't check it, i only tell you what i think and maybe or indeed is not correct but the evolution is a slow process then maybe the first egg wasn't like it is now and the first chicken wasn't like it is now, and the evolution is a process is not a discrete function. i don't think is possible to know the answer . now , after have written this i have found a theory that tell that first was the chicken because during the life an animal cannot change its dna than the first chicken was born from an egg of another bird , this is a theory that i red on wikipedia