12.5" Placenticeras Ammonite With Phragmocone

This is a uniquely prepared Placenticeras meeki ammonite collected in Pennington County, South Dakota. The pattern around the ammonite is the remaining portion of the phragmocone where the outer portion of the ammonite had weathered away. They lobes of the phragmocone were partially prepared. The ammonite is 12.5" wide if you include the weather phragmocone.

It's Late Cretaceous in age (Upper Campanian Stage) or approximately 75 million years old. Back at this time South Dakota was covered by a shallow inland sea. These ammonites are found in hard concretions, or balls of rock which form around the fossil. These concretions are split open to reveal the ammonites which then must be expertly prepared from the surrounding rock, a very time consuming task requiring a lot of skill.

There is a tiny bit of restoration at the very center of the ammonite.