Description
Genuine Osperlioceras authezini Ammonite Fossil
This genuine ammonite fossil is identified as Osperlioceras authezini and originates from Aveyron in the Occitanie region of southern France. It dates from the Upper Toarcian of the Lower Jurassic and is recorded from the Insigne Zone, providing the specimen with detailed geological and biostratigraphic provenance.
This ancient marine cephalopod lived during the closing part of the Early Jurassic, when extensive warm seas covered large areas of what is now France. Its preserved shell offers a direct connection to a marine ecosystem that existed approximately 175 million years ago.
The fossil has been carefully chosen for its recognisable ammonite form, scientific interest and documented Aveyron origin. The listing photographs show the exact specimen you will receive, allowing its natural shell profile, preservation, matrix, mineral colouring and individual surface characteristics to be viewed before purchase. Full sizing and scale information are provided in the photographs.
Species Identification and Classification
Osperlioceras authezini belongs to the ammonites, an extinct and exceptionally diverse group of marine molluscs that flourished throughout much of the Mesozoic Era. Ammonites were cephalopods and were therefore related to living squid, cuttlefish, octopuses and nautiluses.
Its broad scientific classification includes:
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Hildoceratoidea
Family: Hildoceratidae
Genus: Osperlioceras
Species: Osperlioceras authezini
Members of this wider ammonite group are recognised through combinations of shell coiling, whorl shape, umbilical width, flank ornamentation, ventral structure and complex suture patterns. These features evolved rapidly during the Toarcian, making hildoceratid ammonites particularly valuable for identifying and correlating Lower Jurassic marine strata.
Streamlined Ammonite Shell Morphology
The shell developed as a planispiral coil, with successive whorls growing around one another within approximately the same plane. The later whorls overlap the earlier growth stages to varying degrees, forming the central opening known as the umbilicus.
Ammonites attributed to Osperlioceras are generally characterised by compressed, relatively streamlined whorls. The shell flanks may be flattened or gently convex and converge towards a narrow ventral region. This creates a more slender profile than the broad, heavily inflated shells developed by many other Jurassic ammonite groups.
The surface ornament can include fine curved ribs, falcoid folds or growth lines. Falcoid ornament follows a gently sickle-shaped path across the flanks, sweeping forwards towards the shell’s outer margin. The strength and spacing of these features may vary throughout growth and can be more apparent on some portions of the fossil than others.
The outer edge of the shell, known as the venter, may carry a pronounced median keel. This continuous ridge is a characteristic feature of many hildoceratid ammonites and contributed to the shell’s distinctive sharp-edged appearance.
Depending upon preservation, the specimen may retain mineral-replaced shell material, an internal sedimentary mould or a combination of these forms. Fine external detail may appear sharper where shell material survives and more subdued where only the internal mould is exposed.
Ammonite Growth and Chambered Anatomy
The original shell was internally divided by curved partitions called septa. These created a sequence of chambers connected by a narrow tube known as the siphuncle.
The living ammonite occupied only the final and largest body chamber. As it grew, it added shell material at the aperture, moved forwards and sealed the older section behind itself with another septum. This process gradually produced the chambered spiral preserved in the fossil record.
The abandoned chambers formed part of the animal’s buoyancy apparatus. By regulating the balance of liquid and gas within them, the ammonite could control its position in the Jurassic water column.
Where the septa joined the outer shell wall, they formed intricate lines called sutures. These patterns are important in ammonite classification and provide palaeontologists with evidence for distinguishing families, genera and evolutionary lineages.
The soft-bodied animal would have extended its head, eyes and muscular arms from the shell opening. It probably fed upon small marine animals, planktonic organisms and organic material encountered within the surrounding sea.
Upper Toarcian Insigne Zone
This specimen is recorded from the Insigne Zone of the Upper Toarcian. The Toarcian was the final stage of the Lower Jurassic, following the Pliensbachian and preceding the Aalenian of the Middle Jurassic.
The Insigne Zone represents a defined interval within the later Toarcian succession. Such biozones are recognised through characteristic ammonite assemblages and allow fossil-bearing rocks to be placed into a much more precise sequence than a general Jurassic age alone would permit.
Ammonites are especially effective index fossils because many species evolved rapidly, existed for relatively restricted periods and became distributed throughout connected marine basins. Their changing forms allow geologists to correlate sedimentary rocks between separate localities in France and elsewhere in Europe.
The Insigne Zone attribution therefore adds considerable geological value to this specimen. It connects the ammonite with a specific episode in Early Jurassic marine history and helps document the transition towards the ammonite faunas of the succeeding Middle Jurassic.
Early Jurassic Sea of Southern France
During the Upper Toarcian, the region now forming Aveyron lay beneath a warm sea connected with the western margins of the ancient Tethys Ocean. Marine basins and submerged platforms extended across large parts of southern and western Europe.
These waters supported ammonites, belemnites, nautiloids, bivalves, gastropods, brachiopods, crustaceans, fish and marine reptiles. Microscopic plankton formed an essential part of the food web and contributed organic and calcareous material to the sediment accumulating below.
Fine mud, carbonate particles and clay settled across the seabed. Changes in sea level, water circulation, oxygen availability, biological productivity and sediment supply created alternating beds of limestone and marl.
The relatively compressed shell of Osperlioceras authezini would have provided buoyancy and a streamlined profile within this marine environment. The animal lived in the water column above a seabed occupied by numerous shelled invertebrates and other organisms.
Aveyron, Occitanie Fossil Provenance
Aveyron is internationally recognised for its fossil-rich Lower Jurassic rocks and diverse Toarcian ammonite faunas. Natural exposures throughout the department reveal extensive sequences of marine limestone and marl deposited within ancient sedimentary basins.
These rocks have produced ammonites representing many successive stages of Toarcian evolution. Their occurrence has contributed greatly to the study of Jurassic biostratigraphy, cephalopod diversity and the marine connections that once existed across Europe.
A fossil retaining its species identification, Insigne Zone attribution and regional locality possesses substantially greater scientific and educational context than an ammonite offered without collection information. Its documented Aveyron origin links the specimen directly with one of France’s best-known regions for Toarcian palaeontology.
Natural Fossilisation and Preservation
After the ammonite died, its shell descended to the seabed. Currents, scavenging organisms and sediment movement may have affected the shell before it became completely buried.
Fine marine sediment entered the empty chambers and accumulated around the exterior. As further layers were deposited, pressure compacted the sediment and gradually transformed it into sedimentary rock.
The original shell consisted primarily of aragonite, a form of calcium carbonate that may dissolve, recrystallise or be replaced by other minerals during fossilisation. Sediment filling the chambers could harden into an internal mould that preserved the ammonite’s coiled shape, ventral profile and surface ornamentation.
Natural fractures, incomplete edges, worn areas, matrix deposits, mineral markings and colour variations are authentic consequences of burial and geological alteration. These characteristics form part of the specimen’s individual history and ensure that every genuine fossil is unique.
Actual Specimen and Certificate of Authenticity
This is a genuine fossil specimen rather than a cast, replica or artificial reproduction. The listing photographs show the exact Osperlioceras authezini ammonite that will be supplied, allowing its natural shell profile, ornamentation, matrix, mineral colouring and individual state of preservation to be examined before purchase.
Full sizing is shown in the listing photographs.
The fossil includes a generic Certificate of Authenticity card carrying a lifetime guarantee. Its streamlined hildoceratid form, Upper Toarcian age, Insigne Zone attribution and documented Aveyron provenance make it an excellent addition to a Jurassic ammonite collection, French fossil display, natural-history cabinet or educational geological collection.
Reviews
There are no reviews yet.