The effigy mounds may have been built by the Winnebago who fled northward when the Lenape crossed the Mississippi. They are thought to have remained in southern Wisconsin during the Lenap’Alligewi war, and in the end were there to welcome the fugitives back when they returned. This may explain why the Winnebago are isolated in the west from the other Dakota tribes. It is also worthy to note that the Winnebago is oldest dialect of the western Dakota and are called “grandfathers” by the other tribes.
We certainly have a tie between the later effigy mounds built by the Dakota in Minnesota, Wisconsin and Iowa and the effigies found in Ohio. The alligator mound, the Tarleton Cross and the bird effigies within the circular works at Newark are all very similar to what are found to the northwest.