Which came first, the chicken or the egg?

“Eggs existed long before chickens,” according to On Food and Cooking: The Science and Lore of the Kitchen by Harold McGee. “The first eggs were released, fertilized, and hatched in the ocean. Around 250 million years ago, the earliest fully land-dwelling animals, the reptiles, developed a self-contained egg with a tough, leathery skin that prevented fatal water loss. The eggs of birds, animals that arose some 100 million years later, are a refined version of this reproductive adaptation to life on land. Eggs, then, are millions of years older than birds. Gallus domesticus, the chicken more or less as we know it, is only a scant 4 or 5 thousand years old.”