Description
Genuine Pleuroceras spinatum Ammonite Fossil
This carefully chosen fossil is a genuine Pleuroceras spinatum ammonite originating from France. It dates from the Lower Jurassic and is characteristic of the Upper Pliensbachian, immediately before the beginning of the Toarcian Stage. The species is especially significant because it gives its name to the Spinatum Ammonite Zone, one of the principal biostratigraphic divisions used to identify the youngest part of the Pliensbachian.
The photograph shows the actual fossil specimen you will receive, allowing its natural colour, preservation, shell shape, matrix and visible ornamentation to be examined before purchase. Full sizing and scale information can be seen in the accompanying photograph.
Upper Pliensbachian Lower Jurassic Geology
The Pliensbachian was the third major stage of the Lower Jurassic, following the Sinemurian and preceding the Toarcian. During this interval, extensive shallow seas covered large areas of western Europe, including much of present-day France. Sediment accumulated across continental shelves and marine basins, preserving ammonites, belemnites, bivalves and other organisms that inhabited the Jurassic seas.
Pleuroceras spinatum is associated with the uppermost Pliensbachian Spinatum Zone. This ammonite zone is commonly divided into the Apyrenum and Hawskerense subzones and is used by palaeontologists to recognise and correlate rocks deposited shortly before the Pliensbachian–Toarcian boundary.
After the animal died, its shell settled on the seabed and was gradually covered by sediment. Over millions of years, burial, compaction and mineral-rich groundwater transformed the remains into stone. Depending on local conditions, an ammonite may be preserved as original shell material, a mineralised shell, an internal mould or a combination of these forms.
Distinctive Pleuroceras spinatum Morphology
Pleuroceras spinatum was formally named by Jean-Guillaume Bruguière in 1789 and was later placed within the genus Pleuroceras. It belongs to the family Amaltheidae, superfamily Eoderoceratoidea and order Ammonitida.
The species is recognised for its strongly ornamented, planulate shell. Planulate ammonites possess relatively evolute coiling, meaning that a substantial portion of the earlier whorls remains visible within the central umbilical area.
Typical examples display strong radial ribs extending across comparatively flat flanks. These ribs commonly terminate in prominent ventrolateral tubercles near the outer edge of the shell. The whorl section is generally quadrate, while the broad outer surface, known as the venter, carries a distinctive serrated or crenulated keel. Together, these features give Pleuroceras a robust and highly recognisable appearance.
The strength of the ribbing, tubercles and keel can vary according to the ammonite’s growth stage and the conditions under which the fossil was preserved. Natural weathering, mineral replacement and areas of retained matrix may also influence which anatomical features remain visible on an individual specimen.
An Extinct Marine Cephalopod
Ammonites were marine cephalopods related to living squid, cuttlefish, octopuses and nautiluses. The animal occupied the final and largest section of its coiled shell, known as the body chamber. The earlier portion was divided into a succession of smaller chambers by internal walls called septa.
A narrow tube called the siphuncle passed through these chambers and enabled the ammonite to regulate buoyancy by controlling the balance of fluid and gas inside the shell. This chambered structure allowed the animal to remain suspended and move through different levels of the water column.
The shell grew continuously throughout life. As the ammonite increased in size, it produced new shell material around the opening and moved forward into a larger body chamber. Earlier chambers were sealed behind it, preserving a record of growth from the juvenile inner whorls to the mature outer shell.
Importance as a Jurassic Index Fossil
Ammonites are among the most valuable index fossils used in Jurassic geology. They evolved rapidly, occurred across wide marine regions and often existed for comparatively restricted spans of geological time. These characteristics allow particular ammonite species to identify the relative age of the rocks in which they occur.
The Spinatum Zone can be recognised across parts of France, Britain and continental Europe. Fossils of Pleuroceras spinatum therefore help palaeontologists compare geographically separated rock sequences and reconstruct the changing marine environments of the latest Pliensbachian.
French Jurassic Fossil for Collection and Display
France contains extensive exposures of fossil-bearing Jurassic sedimentary rock. During the Early Jurassic, its marine environments formed part of a wider European seaway in which ammonites were abundant and diverse. The preservation of these shells provides direct evidence of the creatures that occupied those vanished seas.
This fossil would make an excellent addition to an ammonite collection, French fossil display, Jurassic cabinet or educational geological collection. Its distinctive ribbing, important zonal association and classic coiled form also make it an appealing display piece or gift for a fossil collector, palaeontology enthusiast or geology student.
Genuine Specimen with Certificate of Authenticity
This is a genuine fossil and not a modern replica or manufactured reproduction. It includes a generic Certificate of Authenticity card carrying our lifetime guarantee of authenticity.
Each fossil is individually selected for its natural appearance, scientific interest and suitability for collection or display. Small fractures, missing shell areas, mineral deposits, matrix attachments, weathering and variations in surface texture are normal features of authentic fossils and form part of the specimen’s geological history.
Fossil: Pleuroceras spinatum
Fossil type: Ammonite
Family: Amaltheidae
Superfamily: Eoderoceratoidea
Order: Ammonitida
Ammonite zone: Spinatum Zone
Geological stage: Upper Pliensbachian
Geological period: Lower Jurassic
Locality: France
Authenticity: Genuine specimen with Certificate of Authenticity lifetime guarantee card
Sizing: Full sizing can be seen in the photograph
Specimen supplied: The photograph shows the actual fossil you will receive
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