Nice, 2.55" Sphenodiscus Ammonites - South Dakota

This is a nicely prepared cluster of ammonite fossils from the Fox Hills Formation of Dewey County, South Dakota. The main ammonite is a beautiful, 2.55" wide Sphenodiscus and there are several smaller partial ammonites present. It is a very displayable piece, that shows well.

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.