Here is an interesting OLD ARTICLE,
this is from the New York Times published in June 1883.
Click on the blue button "view full article" to see the PDF of the original article, which describes hundreds of unusual skulls with double rows of teeth and strange shapes, very interesting...

AN ANCIENT FORT DISCOVERED.;
EARTH-WORKS CONTAINING MANY SKULLS FOUND IN DAKOTA.

CHICAGO, June 21.--A special to the Tribune from Redfield, Dakota, says: "Several parties at work on a farm four and a half miles south of Redfield have discovered an old fort, which occupied nearly two acres, and from which nearly 200 human skulls have been exhumed...
http://query.nytimes.com/gst/abstrac...609C94629FD7CF