The find has experts puzzled, as it is the first of its kind to be outside of a major pyramid or temple complex, and was in a simple mound, easy to overlook.
Christopher Morehart, an archaeologist with the Georgia State University, is credited with the find in Xaltocan, a farming village north of Mexico City.
Morehart told AP, "The interesting question is, why are we seeing this kind of sacrificial act that we often associate with something like Teotihuacan or a big center. Why do we see this … in a place that's not associated with these cities?"
According to Morehart, the Xaltocan mound "is like a bump in the landscape that you could really easily walk over and not know you're standing on it."
Morehart said that carbon dating of the skulls suggested they were at least 1,100 years old and that most were from men.
Apparently the skulls were also found with a shorter length of vertebrae attached, which suggests that the decapitation cut was made closer to the base of the skull. Morehart also said that several of the skulls were found with finger bones inserted into the eye sockets.
He said, "It was common enough that it was intentionally placed there in the eye socket," but he did say that the ritual significance of that remains unclear.
Ironically Morehart and his colleagues stumbled across the site while using Google Earth to investigate ancient waterworks surrounding the ancient kingdom of Teotihuacan.
Probably dating to a time between 660 and 860 AD, the heads appeared to have been carefully placed in rows, or small mounds, and most face east towards the rising sun.
Abigail Meza Penaloza, a physical anthropologist with the Institute of Anthropology at Mexico's National University is part of a team cleaning and assembling the skulls. Penaloza also reportedly confirmed that it was the first find of its kind, both in terms of the kind of decapitations carried out and also the location.
She told the media that mass sacrifices have often been documented at temple inaugurations of temple closings, but not in the middle of fields, such as in this example.
She also noted that it was unusual that the skulls were from a varied population. Some reportedly practiced cranial deformation and others did not, whereas most groups of sacrifice victims found in the past have been more homogenous.