- Placenticeras meeki
- Cretaceous Age
- Pierre Shale
- South Dakota
- This specimen measures approx. 8.5″ wide. It has had the outer shell polished off of one side to reveal the amazing suture pattern. The other side retains it’s natural outer shell.
Ammonites are an extinct group of marine invertebrate animals similar to the modern nautilus. (Cephalopoda) Like the nautilus, ammonites had a soft body with tentacles that emerged from a hollow chambered shell utilized in the manner of a submarine’s ballast tanks. Ammonites are often identified by their shell ornamentation and the structures of the wall that divide the shell’s chambers.