Prehistoric Plants?

A coworker recently brought me two fossils that were collected by an excavator working near Dewart Lake in Kosciusko County, Indiana. 

Any paleobotanists out there that can provide suggestions as to what this is?  Above is a side view, and below is a top view.

Based on comments to a past post on Get Your Botany On!, I think this may be Sigillaria sp., but I would welcome all suggestions.

Above is a photo of the entire fossil; below is a close-up.

This is well beyond the area of my expertise, so any help is appreciated!