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In Stone Fossils

Sphenodiscus sp. Ammonite | Corson County, South Dakota

$125.00 Regular price

Sphenodiscus sp.

Fox Hills Formation, Corson County, South Dakota

Upper Maastrichtian Late Cretaceous 70 Million Years Ago

Specimen: Approx 3.75"×3"

Matrix: Approx 3"×4.75"x3"

This is a rare, two piece (base and ammonite) Spenodiscus sp. specimen from the Fox Hills Formation of Corson County, South Dakota. Specimen is approx 3.75" wide by 3" and the hard concretion surrounding it has been meticulously prepared to leave it on a free standing base of rock with the Mother of pearl impression.

The ammonite displays beautiful mother-of-pearl colors with distinguished oak leaf sutures. This is an amazing American Ammonite specimen with Mother of pearl throughout its shell.

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.