Dumortieria rhodanica Ammonite Fossil Toarcian Jurassic France

Description

Dumortieria rhodanica Ammonite Fossil from France

Genuine Toarcian Jurassic Specimen

This carefully selected Dumortieria rhodanica ammonite is a genuine fossil from Saint-Quentin-Fallavier in Isère, within the Auvergne-Rhône-Alpes region of France. The photographs show the actual specimen you will receive, allowing its natural preservation, shell form, matrix and colour to be considered before purchase. Please consult the sizing photograph for its full dimensions and proportions.

Lower Jurassic Geological Setting

The specimen dates from the Toarcian Stage of the Lower Jurassic, approximately 183 to 174 million years ago. During this interval, much of western Europe was occupied by warm marine basins linked to the Tethys Ocean. Mud, carbonate sediment and organic material accumulated on the sea floor, preserving a diverse fauna of ammonites, belemnites, bivalves and other marine organisms.

The geology of south-eastern France records changing Jurassic sea levels and environments along the margins of the ancient Tethyan realm. Fossils from a documented locality such as Saint-Quentin-Fallavier retain valuable context, linking an individual specimen with the rocks and ecosystem in which it was preserved.

Species and Shell Morphology

Dumortieria rhodanica belongs to the Ammonoidea, an extinct group of marine cephalopods related to modern squid, cuttlefish, octopus and nautilus. The coiled shell contained chambers separated by septa. The animal occupied the final body chamber, while the chambered portion and a connecting siphuncle contributed to buoyancy control.

Dumortieria is generally placed in the family Hammatoceratidae within the order Ammonitida. Members of the genus often have evolute to moderately involute coiling, a comparatively open umbilicus and distinctive ribbing across the flanks. The species rhodanica is named in reference to the Rhône region. Whorl shape, rib pattern, ventral form and umbilical width are among the features used to distinguish species.

Biostratigraphic Significance

Ammonites evolved rapidly and were widely distributed through Jurassic seas. Characteristic species are therefore used as index fossils to establish biozones and correlate sedimentary layers between different localities. Dumortieria is particularly important in Upper Toarcian successions and helps document the recovery and diversification of ammonite faunas during the later part of the stage.

Fossilisation and Authentic Features

After death, the shell settled onto the seabed and became buried by sediment. Through compaction and mineralisation, original shell material could be preserved, replaced or dissolved to leave an internal mould. Natural fissures, incomplete edges, mineral staining, matrix attachment and weathering are expected features of authentic fossils. Each variation records part of the specimen’s geological history.

Collecting and Display

This French ammonite is suitable for a Jurassic fossil collection, geological teaching display, cabinet of curiosities or natural history arrangement. Its identified species and locality make it particularly appealing to collectors of European ammonites. It is also a thoughtful gift for a geology student or prehistoric marine-life enthusiast. The exact specimen pictured will be supplied.

Certificate and Care

This is a genuine fossil specimen and includes a generic Certificate of Authenticity card with a lifetime guarantee. Handle it over a soft surface, support the fossil and matrix, and avoid pressure on delicate ribs or edges. Keep it dry and stable, away from impact, strong chemicals and rapid changes in humidity or temperature. Gentle dry dusting is recommended.