Description
Genuine Frogdenites Ammonite Fossil from Normandy
This carefully chosen fossil is a genuine Frogdenites sp. ammonite from the Bajocian Stage of the Middle Jurassic, collected in Normandy, France. It represents an extinct marine cephalopod that inhabited the ancient seas of western Europe approximately 170 million years ago.
The designation “sp.” indicates that the fossil has been identified confidently to the genus Frogdenites, while no individual species name has been assigned. This is standard scientific terminology and provides a responsible identification without overstating the level of preservation or diagnostic detail visible in the specimen.
The photograph shows the actual fossil you will receive, allowing its individual shape, preservation, colour, matrix and natural geological features to be examined before purchase. Full sizing and proportions can be seen in the accompanying photograph.
This fossil includes a generic Certificate of Authenticity card with a lifetime guarantee, confirming that it is a genuine specimen.
Fossil Classification and Scientific Interest
Scientific name: Frogdenites sp.
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Geological period: Jurassic
Epoch: Middle Jurassic
Stage: Bajocian
Locality: Normandy, France
The genus Frogdenites was formally established by the British palaeontologist Sydney Savory Buckman in 1921, with Frogdenites spiniger designated as its type species. Modern systematic research recognises Frogdenites as an important early member of a distinctive Bajocian ammonite lineage.
Ammonite genera such as Frogdenites are scientifically valuable because ammonites evolved rapidly and were widely distributed through Jurassic marine environments. Their changing shell forms allow palaeontologists to compare and correlate sedimentary rock layers between geographically separated localities.
Frogdenites Shell Form and Ornamentation
Frogdenites is known for a compact, rounded to globular shell form with an open, clearly defined umbilical region at the centre of the coil. The shell is generally evolute, meaning that the earlier whorls remain relatively visible rather than being completely concealed by the final outer whorl.
The shell surface typically bears numerous fine to moderately developed ribs. These ribs may divide as they travel away from the umbilical area and continue across the rounded outer edge, known as the venter. This combination of rounded whorls, visible inner coiling and regular ribbing gives Frogdenites its characteristic sculptured appearance. Scientific revisions describe related members of this group as small to medium-sized, sphaeroconic ammonites with fine, sharply defined ribs.
The precise strength of the ribbing and the amount of visible whorl detail will depend on the preservation of the individual fossil. Natural wear, sediment attachment, mineral deposits, fractures or incomplete areas are genuine results of burial, fossilisation and later geological exposure.
Bajocian Geology of Normandy
The Bajocian is an internationally recognised stage within the Middle Jurassic. It was named after Bayeux in Normandy, making fossils from this region especially significant to the history of geological science. The stage was introduced during the nineteenth century by the French naturalist and palaeontologist Alcide d’Orbigny, using the Latinised name for Bayeux.
During Bajocian times, Normandy lay beneath warm, shallow seas connected to the broader marine systems surrounding the European landmasses. Layers of carbonate mud, sand, iron-rich sediment and biological debris accumulated across the seabed. These deposits preserved abundant marine fossils, including ammonites, belemnites, bivalves, brachiopods, gastropods, echinoids and other invertebrates.
Bajocian strata in Normandy include historically important fossil-bearing formations around Bayeux, Caen and other areas of Calvados. Detailed studies of these deposits have demonstrated their rich ammonite successions and their importance for reconstructing Middle Jurassic marine environments and biostratigraphy.
Life in the Middle Jurassic Sea
Ammonites were molluscs related to modern squid, cuttlefish, octopuses and nautiluses. The living animal occupied the largest outer chamber of its shell, while the inner portion was divided into a sequence of smaller chambers by walls called septa.
A tube known as the siphuncle connected these chambers and helped the animal regulate its buoyancy. By controlling the balance of gas and liquid inside the shell, the ammonite could maintain its position within the water column. Movement was achieved by drawing water into the mantle cavity and expelling it through a muscular funnel, producing a form of jet propulsion.
The animal probably used tentacles around its mouth to capture small marine organisms or collect food particles. Its ribbed shell provided structural strength while also creating the distinctive ornamentation now preserved in the fossil record.
Natural Fossilisation and Preservation
After the ammonite died, its shell settled onto the Jurassic seabed. Burial beneath sediment protected it from complete destruction. Over millions of years, the surrounding deposits became compacted and cemented into sedimentary rock.
The original shell material could be replaced by minerals, preserved as a thin shell layer or dissolved to leave a mould. Sediment entering the empty shell formed an internal cast that could retain the whorl shape, ribbing and other external details. Iron minerals, calcite and other naturally occurring compounds may contribute to the fossil’s colour and surface texture.
Every fossil has undergone a different history of burial, mineralisation, compression, erosion and exposure. These processes create the individual characteristics that distinguish one specimen from another.
Authentic Jurassic Collectable
This Frogdenites sp. ammonite is suitable for fossil collectors, ammonite enthusiasts, geology students, educational collections and natural-history displays. Its recognised genus, Bajocian age and Normandy provenance give it particular appeal as a genuine piece of European Jurassic history.
It can be displayed in a fossil cabinet, office, classroom, study or home collection. The specimen also makes an unusual natural-history gift for anyone interested in palaeontology, geology, prehistoric marine life or the Jurassic Period.
The photograph shows the exact 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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