This is a rare, Hoploscaphites spedini from the Fox Hills Formation of South Dakota. Specimen is approx 4.5" wide and the hard concretion surrounding it has been meticulously prepared to leave it on a free standing base of rock.
The ammonite displays beautiful mother-of-pearl colors with distinguished bumpy nodes along the outer edges.
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 underwent many tedious hours of fossil preparation to remove the hard matrix surrounding the fossil.