Description
Genuine Osperlioceras Ammonite Fossil from France
This genuine Osperlioceras alternans subcostulatum ammonite fossil originates from Aveyron in Occitanie, southern France. It was preserved within marine deposits dating to the Middle Toarcian Stage of the Lower Jurassic Period, making it an appealing specimen for ammonite collectors, fossil enthusiasts and anyone interested in European Jurassic palaeontology.
The fossil has been carefully selected for its individual character and natural geological detail. The photographs show the actual specimen you will receive, rather than a representative example. Any natural matrix, surface texture, mineral deposits, weathering, minor imperfections or areas of incomplete preservation form part of the fossil’s authenticity and history.
Full sizing and scale information can be seen in the accompanying photographs.
Middle Toarcian Subcostulatum Zone
This ammonite is recorded from the Subcostulatum Zone, a biostratigraphic interval within the Toarcian. Ammonites are especially valuable to palaeontologists because many genera and species evolved rapidly and had comparatively limited geological ranges. Their remains can therefore be used as index fossils to correlate marine sedimentary layers across different localities.
Published studies of the Toarcian genus Osperlioceras recognise O. subcostulatum and O. alternans among related forms characterised by relatively widely spaced ribbing during juvenile growth. Researchers have also documented considerable variation during the development of the shell, demonstrating the importance of examining rib density, coiling and proportions at different growth stages.
The Subcostulatum interval represents part of the later evolutionary development of Osperlioceras, a genus that diversified into several shell forms during the Toarcian. This makes specimens associated with the group particularly interesting for studying ammonite growth, variation and evolutionary relationships.
Ammonite Form and Shell Characteristics
Osperlioceras was a coiled marine cephalopod with a chambered shell. During life, the animal occupied the final outer chamber, while the older internal chambers helped regulate buoyancy. The chambers were divided by septa, whose intersections with the outer shell created the intricate suture patterns characteristic of ammonites.
Members of this genus generally display an evolute to moderately involute shell form, depending on species and growth stage. The coiling may leave part of the earlier whorls visible around the umbilicus. Ornamentation typically includes curved or slightly flexuous ribs extending across the shell’s flanks, with rib strength and spacing changing as the ammonite grew.
The name subcostulatum refers to the ribbed character associated with this ammonite form. Such ornamentation would have strengthened the shell while also providing palaeontologists with useful features for identification and comparison.
Scientific Classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Hildoceratoidea
Genus: Osperlioceras
Form: Osperlioceras alternans subcostulatum
Ammonites were distant relatives of modern cephalopods such as squid, cuttlefish, octopuses and the chambered nautilus. They were among the most diverse and widespread marine animals of the Mesozoic Era before becoming extinct at the end of the Cretaceous Period.
Jurassic Marine Environment of Aveyron
During the Toarcian, the region now forming southern France lay beneath or close to warm marine waters connected with the western Tethyan realm. Fine sediment accumulated on the seabed, occasionally burying shells and other organic remains before they were destroyed by scavenging, erosion or physical disturbance.
Over millions of years, continued burial compacted these sediments into rock. Mineral-rich groundwater entered the buried shell and surrounding sediment, preserving part or all of the ammonite as fossil material. The result is a tangible remnant of the marine ecosystems that occupied France during the Early Jurassic.
Toarcian ammonite assemblages are important for reconstructing ancient marine geography and for comparing the timing of sedimentary deposits across Europe and the wider Tethyan region. Research into Toarcian ammonoids has shown their value in understanding changes in diversity, distribution and palaeoceanographic conditions during this interval.
Actual Specimen and Certificate of Authenticity
This is a 100% genuine fossil specimen and not a replica, cast or modern reproduction. It includes a generic Certificate of Authenticity card with a lifetime guarantee, providing lasting reassurance regarding its genuine fossil status.
The ammonite is suitable for:
- Jurassic fossil and ammonite collections
- Educational geology and palaeontology displays
- Natural-history cabinets and curiosity collections
- Home, office or study decoration
- Fossil gifts for collectors and enthusiasts
- Comparative or reference collections
Every fossil is naturally unique. The specimen shown in the photographs is the exact Osperlioceras alternans subcostulatum ammonite that will be supplied, allowing its preservation, colour, matrix and individual characteristics to be examined before purchase.
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