Fox Hills Formation, South Dakota
Upper Maastrichtian, Late Cretaceous 70 Million Years Ago
Specimen: Approx 2.75"×3"
Matrix: Approx 2"×3.5"x3"
This is a rare Spenodiscus sp. specimen from the Fox Hills Formation of Corson County, South Dakota. Specimen is approx 2.75" wide by 3" and the hard concretion surrounding it has been meticulously prepared to leave it on a free standing base of rock. This particular specimen has pelecypod impressions in the matrix.
The ammonite displays has some beautiful mother-of-pearl colors. This is an amazing American Ammonite.
This 70 million year old ammonite 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.
The mother-of-pearl is usually formed by the fossilization process into calcite. There are only a few localities in the world where it preserved unchanged, with a fiery sheen. As well as the rarity of its form of preservation, the scaphite is a scarce late-form ammonite so-named from the Greek "scooped out" for the gradual "unwinding" of the ammonite's familiar coiled shape. The scaphites would later develop into an almost completely unfurled heteromorph.