Polished Ammonite Fossil Half SliceA smooth, polished Ammonite fossil sliced in half, allowing you to view of the interior of this ancient creature. Beautiful as a decorative piece, on a stand, or shadowbox framed with other natural wonders. Preserve and admire natural history with this exceptional piece. Ammonite Fossil Ammonites began appearing over 410 million years ago, during the Early Devonian period, vanishing soon after the Cretaceous mass extinction event 66 million years ago.