As Americans get ready to carve Thanksgiving turkeys, ponder this question: When was this famous fowl first tamed?

Archaeologists are not exactly sure, but recent research suggests that humans domesticated the big bird at least 1,500 years ago. The evidence comes from a clutch of intact eggs found in an old fortress in Oaxaca, Mexico. The researchers believe that the eggs, which date to between 400 and 500 A.D., were used by ancient people as some sort of ritualistic offering or sacrifice to their gods.

“Finding those eggs intact was mind-blowing,” said Gary Feinman, an archaeologist from the Field Museum in Chicago. “I’ve been excavating for decades and I have never ever found intact eggs like that in that quantity ever.”