Sphenodiscus lenticularis Ammonite Fossil – Fox Hills Formation, South Dakota, USA

This genuine Sphenodiscus lenticularis ammonite fossil comes from the Fox Hills Formation at Timber Lake, South Dakota, USA, and dates to the Maastrichtian Stage of the Late Cretaceous Period. This carefully chosen fossil specimen includes a Certificate of Authenticity lifetime guarantee generic card, giving collectors confidence that they are purchasing a genuine fossil. Full sizing can be seen in the photo, and the fossil shown is the actual specimen you will receive.

Geology and Age

The Fox Hills Formation is a famous Late Cretaceous geological unit of the Western Interior of North America. It represents marine and marginal marine sediments deposited as the Western Interior Seaway gradually retreated from the continent near the end of the Cretaceous Period. These rocks preserve an important record of ancient shorelines, shallow seas, coastal environments and the marine life that lived there shortly before the extinction of the ammonites.

This specimen dates to the Maastrichtian Stage, the final stage of the Cretaceous Period. This makes Sphenodiscus lenticularis especially interesting to fossil collectors, as it comes from the last chapter of ammonite evolution before the end-Cretaceous extinction event. The Maastrichtian seas were home to a wide range of marine organisms, including ammonites, bivalves, gastropods, fish, sharks, marine reptiles and other invertebrates.

Timber Lake, South Dakota is located within a region well known for Late Cretaceous fossil material. Fossils from the Fox Hills Formation are prized because they capture the final marine ecosystems of the Western Interior Seaway, a vast ancient sea that once split North America into eastern and western landmasses.

Fossil Type and Species

This specimen is identified as Sphenodiscus lenticularis, a distinctive Late Cretaceous ammonite species. Ammonites were extinct marine cephalopods related to modern squid, cuttlefish and nautilus. They had coiled, chambered shells, with the living animal occupying the final outer chamber while the inner chambers helped regulate buoyancy.

Sphenodiscus belongs to the order Ammonitida and is commonly associated with the family Sphenodiscidae and superfamily Acanthoceratoidea. The genus is known for its compressed, disc-like shell form, which gives many specimens a smooth, flattened and elegant appearance. The species name lenticularis reflects this lens-shaped form, making it a particularly recognisable ammonite among Late Cretaceous collectors.

Morphology and Natural Features

Sphenodiscus lenticularis is admired for its distinctive shell shape. Unlike many strongly ribbed ammonites, this species is often relatively smooth, compressed and rounded, with a streamlined, lens-like profile. This morphology gives the fossil a clean and attractive display quality while also showing the diversity of ammonite forms that existed during the Late Cretaceous.

The shell would originally have been divided into internal chambers by septa. These chambers were connected by a siphuncle, allowing the ammonite to control gas and fluid balance for buoyancy. The complex suture lines formed where the internal septa met the shell wall are an important feature in ammonite classification and are part of what makes these fossils so scientifically fascinating.

As a living animal, Sphenodiscus lenticularis would have inhabited marine waters of the Western Interior Seaway during the very end of the age of dinosaurs. It was part of a rich marine ecosystem and would have shared its environment with fish, sharks, mosasaurs, turtles, bivalves and other Late Cretaceous sea life.

Collector Appeal

A Sphenodiscus lenticularis ammonite from the Fox Hills Formation is a highly desirable fossil for collectors of Cretaceous ammonites, American fossils, marine fossils and extinction-era specimens. Its Maastrichtian age makes it especially appealing because it represents one of the final ammonite faunas before the group disappeared at the end of the Cretaceous.

This fossil is suitable for a fossil cabinet, educational collection, geology display, natural history collection or themed display of prehistoric marine life. Its South Dakota locality, Fox Hills Formation origin and distinctive ammonite form all add to its collector value and geological interest.

Authenticity and Presentation

This is a genuine fossil specimen and includes a Certificate of Authenticity lifetime guarantee generic card. The specimen has been carefully selected, and the listing photograph shows the actual fossil you will receive, allowing buyers to view its preservation, shape and natural character before purchase.

This authentic Sphenodiscus lenticularis ammonite fossil from the Maastrichtian Fox Hills Formation of Timber Lake, South Dakota is an excellent choice for fossil collectors, ammonite enthusiasts, geology displays and anyone seeking a genuine piece of Late Cretaceous marine history.