RARE 9″ Acanthoceras rhotomagense Fossil Chalk Ammonite Lower Cenomanian Cretaceous Lewes Kent – Genuine Collector Specimen with COA

Description

Rare Acanthoceras rhotomagense from the Lower Cenomanian

This impressive 9-inch Acanthoceras rhotomagense fossil ammonite is a remarkable specimen from the Lower Cenomanian stage of the Cretaceous period, expertly preserved in the chalk deposits of the Southerham Grey Pit, Lewes, Kent, England. Known for their striking ribbed shells and historical importance as index fossils, Acanthoceras ammonites are sought after by both collectors and palaeontologists. The specimen pictured is the exact fossil you will receive, chosen for its scientific value, visual appeal, and exceptional preservation.

Geological Age & Provenance

The Lower Cenomanian stage (approximately 100.5 to 97 million years ago) marks the beginning of the Late Cretaceous period, a time when southern England was covered by a warm, shallow sea. Over millions of years, the remains of marine organisms settled onto the seafloor, forming the fine, white chalk for which the region is famous. The Southerham Grey Pit is part of the Lewes Chalk sequence and is one of the classic fossil localities in the UK, yielding ammonites, belemnites, marine reptiles, and other marine life from the Cenomanian.

Species Profile & Classification

Acanthoceras rhotomagense belongs to the family Acanthoceratidae, superfamily Acanthoceratoidea, and order Ammonitida. This species is easily recognised by its robust, evolute shell, strong ribbing, and prominent tubercles along the flanks. The venter (outer rim) features ribs that continue across uninterrupted, a diagnostic feature of this genus. As a member of the Acanthoceratidae, it served as an important index fossil, enabling precise dating of Cenomanian strata across Europe and beyond.

Morphology & Key Features

This specimen shows the classic characteristics of Acanthoceras rhotomagense:

• Prominent radial ribs extending from the umbilicus to the venter.
• Tubercles at regular intervals, giving the shell a spiny texture in life.
• Evolute coiling, with all whorls visible from the side.
• Large size at 9 inches, indicating a mature individual.

The ammonite’s shell was originally composed of aragonite, which in most chalk specimens has been replaced by calcite, preserving its intricate details. Its chambered phragmocone allowed the animal to regulate buoyancy, while the outer living chamber housed the soft body.

Paleoenvironment & Life History

During the Cenomanian, the chalk seas of southern England were teeming with marine life, from tiny plankton to large predatory reptiles. Ammonites like Acanthoceras rhotomagense were active swimmers and opportunistic predators, feeding on smaller molluscs, crustaceans, and other invertebrates. Their shells, after the animals died, often sank to the seafloor where they were rapidly buried in fine carbonate mud, aiding their exceptional preservation.

The Southerham Grey Pit’s geological setting provides valuable insights into the marine ecosystems of the Late Cretaceous, and fossils from this site are highly regarded in both academic collections and private displays.

Collector Value

• Species: Acanthoceras rhotomagense – a well-documented index fossil species.
• Size: Large 9″ diameter, suitable for display.
• Origin: Southerham Grey Pit, Lewes, Kent, England.
• Preservation: Excellent surface detail with clear ribbing and tuberculation.
• Authenticity: 100% genuine, supplied with a Certificate of Authenticity.

This large and well-preserved Acanthoceras rhotomagense is an exceptional addition to any fossil collection, combining scientific significance with impressive visual presence, and representing a true piece of England’s Cretaceous marine heritage.