In the Maya belief system, specifically, the soul could be divided into four separate parts. "Baah," which means the self represented by the head, and represents one's life force. "Ik'" represented the breath of the soul and was associated with wind, jade, and teeth. "Ch'ulel" was the essence which resided in the heart and blood, and finally, "wahy" were companion spirits, typically animals, who would die after their human counterpart passed on.
Since an ancestor's soul did not necessitate their entire body to be present, parts of it could be used to communicate with their descendants, such as the skull, mandible, teeth, or arm.
However, typically when such remains are found secondary to a primary burial, they were interpreted as evidence of ritual violence, offerings, and sacrifices either for the primary deceased, gods, or buildings.
Exactly, define a reliable source?