Description
Genuine Strenoceras gerentianum Ammonite Fossil
This carefully chosen specimen is a genuine Strenoceras gerentianum ammonite fossil from Caen in Calvados, Normandy, France. Dating from the Bajocian Stage of the Middle Jurassic, it represents an extinct marine cephalopod that lived in the ancient seas covering north-western Europe approximately 170 million years ago.
The fossil’s coiled form and strongly ornamented shell make it an attractive example of Jurassic marine life, suitable for an established fossil collection, educational display or natural-history cabinet. The photograph shows the exact specimen you will receive, so its individual preservation, ribbing, colour, shape, matrix and natural geological characteristics can be examined before purchase.
Full sizing and proportions are shown in the accompanying photograph. This authentic fossil is supplied with a generic Certificate of Authenticity card carrying a lifetime guarantee.
Fossil Classification and Geological Information
Scientific name: Strenoceras gerentianum
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Stephanoceratoidea
Geological period: Jurassic
Epoch: Middle Jurassic
Stage: Bajocian
Locality: Caen, Calvados, Normandy, France
Strenoceras is a recognisable genus of strongly ornamented Bajocian ammonites. Members of the genus are valued by collectors and palaeontologists for their distinctive shell sculpture and their usefulness in the study of Middle Jurassic rock successions.
Ammonites evolved rapidly and were widely distributed through Jurassic seas. This makes particular species valuable as biostratigraphic fossils, helping geologists compare sedimentary layers from different localities and establish their relative ages.
Distinctive Strenoceras Shell Morphology
Strenoceras gerentianum is characterised by an evolute coiled shell in which the central umbilical area is comparatively open and portions of the earlier whorls remain visible. The whorls are decorated with prominent ribs that create the strongly sculptured appearance typical of the genus.
Primary ribs arise near the inner edge of the whorl and extend across the flanks. They may divide into secondary ribs as they approach the outer part of the shell. Raised nodes or tubercles can also occur around the ventrolateral region, depending on the individual’s growth stage and the degree of preservation.
The outer edge of an ammonite shell is known as the venter. In Strenoceras, this area may show strong ornamentation and a characteristic division between the ribbed sides of the shell. These features distinguish the genus from many smoother or more tightly coiled ammonites found in other Jurassic deposits.
The precise visibility of the ribs, whorls, tubercles and central coiling varies naturally between specimens. Any incomplete areas, mineral deposits, surface wear, attached matrix or differences in texture are authentic geological features resulting from fossilisation and later exposure.
Bajocian Geology of Caen and Calvados
Caen lies within the Calvados department of Normandy, an area internationally recognised for its Middle Jurassic rocks and abundant marine fossils. The name Bajocian is derived from the Latin name for Bayeux, another historic town in Calvados, reflecting Normandy’s importance in the development of Jurassic geological classification.
During Bajocian times, the region formed part of a shallow marine environment connected to the broader Jurassic seas of western Europe. Sediments accumulated across the seabed as layers of limestone, carbonate mud, sand, clay and locally iron-rich material.
These deposits preserve a rich marine fauna that may include ammonites, belemnites, brachiopods, bivalves, gastropods, echinoids and other invertebrates. Changes in water depth, sediment supply, marine currents and oxygen conditions influenced the types of rock deposited and the fossils preserved within them.
The ammonite-bearing strata of Normandy have played an important role in the study of Jurassic biostratigraphy. Their varied ammonite assemblages allow individual sections of Bajocian time to be divided into increasingly detailed zones and faunal intervals.
Life in the Middle Jurassic Sea
Ammonites were marine molluscs related to living squid, cuttlefish, octopuses and nautiluses. The living animal occupied the largest outer section of its shell, called the body chamber. The inner portion of the shell was divided into smaller chambers by curved walls known as septa.
A narrow tube called the siphuncle passed through these chambers and helped regulate the balance of gas and liquid within them. This allowed the ammonite to control its buoyancy and maintain its position in the water column.
Movement was achieved using jet propulsion. Water was drawn into the mantle cavity and expelled through a muscular funnel, pushing the animal in the opposite direction. Tentacles around the mouth were probably used to capture small prey, gather food and explore the surrounding marine environment.
The shell grew continuously as the animal matured, with new material added around its opening. Its ribs and changing whorl proportions therefore record part of the ammonite’s growth history.
Natural Fossilisation and Preservation
After death, the ammonite shell sank to the Jurassic seabed. Its soft tissues decayed while the shell became buried beneath layers of sediment. Sediment could enter the empty shell chambers, gradually forming a detailed internal cast.
Over millions of years, pressure compacted the surrounding deposits and mineral-rich groundwater altered both the shell and the sediment. The original aragonitic shell material could be replaced by other minerals, recrystallised or dissolved to leave a mould preserving the animal’s form.
Natural fractures, weathered sections, matrix attachments, mineral staining and incomplete areas are normal characteristics of genuine fossils. Each specimen has experienced a unique history of burial, mineralisation, geological movement and erosion, making every ammonite individually distinctive.
Authentic Middle Jurassic Collectable
This Strenoceras gerentianum ammonite is suitable for fossil collectors, geology students, ammonite enthusiasts and anyone interested in prehistoric marine life. Its identifiable species, bold ribbed morphology and classic Normandy provenance give it strong educational, geological and display appeal.
It can be presented in a fossil cabinet, study, office, classroom or natural-history collection. It also makes an unusual gift for a collector or anyone fascinated by palaeontology and the Jurassic Period.
The photograph shows the actual carefully chosen fossil specimen you will receive. Full sizing can be seen in the photo. A generic Certificate of Authenticity card with a lifetime guarantee is included.
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