2.3" Sphenodiscus Ammonite Cluster- South Dakota

This is a beautiful 2.3" Sphenodiscus ammonite specimen from the Fox Hills Formation of South Dakota. It's been wonderfully prepared from the hard concretion it was found in. The rock has many other micro fossils still in the rock, like small fossil clams and gastropods.

These 70 million year old ammonites lived when South Dakota was a shallow inland sea. It was found preserved in a concretion that was split open. It then had to be hand prepared to remove the hard rock surrounding it from the shell, a very time consuming task.