2.5" Fossil Nautilus (Eutrephoceras) - South Dakota

A nautilus's shell is made up of two layers. The inner layer has the iridescent shine, while the outer layer provides protection from external forces. Inside the shell are septa that divide the living area of the shell into compartments and help the animal maintain balance and position in the water column.

Nautilus are "living fossils": species similar to this one still exist in our oceans!

These 70 million year old ammonites lived when South Dakota was a shallow inland sea. They were found preserved in concretions when split open. They then had to be hand-prepared to remove the hard rock surrounding them from their shells, a very time consuming task.