Fossil Ammonite
Ammonites are an extinct group of marine animals similar to the nautilus. Like the nautilus, ammonites had a soft body with tentacles that emerged from a hollow chambered shell filled with gas for buoyancy.
Ammonites are among the most common fossils found in collections, being plentiful in locations all over the world. They became extinct at the end of the Cretaceous Period, the same time that the dinosaurs disappeared.
Evolution carries a variety of species of ammonites!
Individual shapes and fossils vary but your item will resemble the pictured example.