The Xiximes believed that ingesting the bodies and souls of their enemies and using the cleaned bones in rituals would guarantee the fertility of the grain harvest, according to historical accounts by Jesuit missionaries.

The newfound bones prove that cannibalism, "was a crucial aspect of their worldview, their identity," said José Luis Punzo, an archaeologist behind the new research.

(Related: "Cannibalism Normal For Early Humans?")

The mountains of what's now Durango state (map) were once home to some 5,000 Xiximes, as well as other indigenous groups.

It was only the Xiximes and the like-minded Acaxées who are said to have been cannibals, though no archaeological evidence for the practice has been found for the Acaxées, said Punzo, of the Durango office of