Rare Sphenodiscus lenticularis Ammonite Fossil South Dakota USA COA

Description

Offered here is the exact Sphenodiscus lenticularis ammonite fossil shown in the photographs. This is a distinctive Upper Cretaceous marine fossil from the Pierre Shale, collected from the southern flank of the Black Hills in South Dakota, USA. The specimen comes from upper Campanian strata, placing it in the later part of the Campanian Stage of the Late Cretaceous. The Campanian spans roughly 83.6 to 72.1 million years ago, so this ammonite represents an animal that lived many tens of millions of years before the end-Cretaceous extinction.

Sphenodiscus is recognised for its strongly involute, compressed and typically lenticular shell form. In an involute ammonite, later whorls cover much of the earlier ones, producing a compact, streamlined profile. The genus belongs to a specialised lineage of ammonites that inhabited the Western Interior Seaway, the immense shallow sea that divided much of North America during the Cretaceous. Its shell was divided internally into chambers. The living animal occupied the final chamber, while the older chambers helped control buoyancy in the water.

The Pierre Shale records the soft marine muds laid down on the floor of that seaway. Today, its rocks are famous for preserving ammonites and many other creatures from a vanished marine ecosystem. Fossils from accurately documented horizons such as these are useful to palaeontologists because ammonites evolved rapidly and were widely distributed. Their changing forms can help researchers compare and correlate rocks of similar age across large geographical areas.

This fossil is sold as a natural specimen and has not been represented as a perfect or complete shell. Please examine every photograph carefully for the precise condition, preservation, colour, surface detail and form. The photographs form an important part of the description and show the actual specimen you will receive, not a stock image or a substitute. Any measurements, scale or views visible in the photographs should be used when assessing size and display suitability.

The piece makes an appealing addition to an ammonite, Cretaceous, Pierre Shale or North American fossil collection. It also works well as an educational example of adaptation in extinct marine cephalopods and of the extraordinary fossil record of the Western Interior Seaway. Its documented locality and stratigraphic information add meaningful scientific context beyond its visual interest.

A certificate of authenticity will accompany the specimen. The certificate records the identification and locality information supplied with this listing and is backed by our lifetime authenticity guarantee. We have prepared the description conservatively so that the buyer can make an informed decision from the photographs and documented details.

Your fossil will be packed carefully for transit. Please retain the accompanying label and certificate with the specimen, as these preserve its provenance and scientific value. This is an opportunity to acquire a genuine Sphenodiscus lenticularis ammonite from the Upper Cretaceous Pierre Shale of South Dakota, offered with clear locality information and the reassurance that the photographed fossil is the one that will be dispatched.