Description
Genuine Sublunuloceras pseudopunctatum Ammonite Fossil
This genuine ammonite fossil is identified as Sublunuloceras (Orbignyceras) pseudopunctatum and originates from Herznach in the canton of Aargau, Switzerland. It dates from the Middle Callovian subdivision of the Middle Jurassic and represents an extinct marine cephalopod that inhabited European seas approximately 165 million years ago.
The name in parentheses, Orbignyceras, records a more detailed taxonomic placement traditionally used for this ammonite within Sublunuloceras. Such notation may indicate a recognised subgenus or closely related morphological grouping. The specimen combines an identifiable ammonite form with precise locality and geological-age information, giving it considerably greater scientific context than an unprovenanced decorative fossil.
This carefully chosen piece is the exact fossil shown in the listing photographs. Its natural shell form, preservation, colour, matrix and individual geological features can therefore be inspected before purchase. Full sizing and scale information are provided in the photographs.
Scientific Classification and Ammonite Group
Sublunuloceras pseudopunctatum belongs to the ammonites, an exceptionally successful group of marine molluscs that flourished throughout much of the Mesozoic Era. Its broad classification includes:
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Haploceratoidea
Family: Oppeliidae
Genus: Sublunuloceras
Subgeneric designation: Orbignyceras
Species: Sublunuloceras pseudopunctatum
Ammonites were related to living squid, cuttlefish, octopuses and nautiluses. Although their external shells resemble those of the modern chambered nautilus, ammonites formed a separate evolutionary lineage with distinctive shell ornamentation and complex internal suture patterns.
The Oppeliidae included many comparatively streamlined Jurassic ammonites. Members of this family often possessed compressed shells, tightly overlapping whorls and delicate ornamentation, contrasting with the heavily ribbed and spiny forms found in some other ammonite groups.
Distinctive Shell Morphology
Sublunuloceras ammonites generally possessed planispirally coiled shells, meaning that the whorls developed around one another within the same plane. Their coiling was commonly involute, with each later whorl covering much of the preceding growth stage and leaving a relatively narrow central umbilicus.
The whorls were typically compressed from side to side, producing a slender, disc-like profile. The outer edge of the shell, known as the venter, may be narrow or gently sharpened rather than broadly rounded. These proportions created an elegant and relatively streamlined shell.
Surface ornamentation can include fine falcoid ribs, growth lines and subdued spiral features. Falcoid ribs follow a gently curved or sickle-shaped course across the flanks. The species name pseudopunctatum suggests a resemblance to a punctate or finely marked form, although the exact expression of surface detail depends strongly upon the specimen’s growth stage and preservation.
The fossil may preserve external shell ornament, a sediment-filled internal mould, mineral replacement or a combination of these features. Naturally worn ribs, incomplete shell areas and differences in surface texture are expected on an authentic Jurassic specimen.
Chambered Shell and Buoyancy System
Internally, the ammonite shell was divided by curved walls called septa. These created a sequence of chambers connected by a narrow tube known as the siphuncle. The living animal occupied only the final and largest chamber, while the earlier chambers formed part of its buoyancy apparatus.
By regulating the balance of fluid and gas within the chambered shell, the ammonite could maintain its position in the water. The intricate lines formed where the septa met the shell wall are called sutures. These patterns are important in ammonite classification and became highly complex in many Jurassic groups.
The animal would have extended its head, eyes and muscular arms from the shell aperture. Its compressed shell suggests a form adapted to movement within the marine water column, although its precise behaviour and feeding strategy cannot be observed directly.
Middle Callovian Geological Age
This fossil dates from the Middle Callovian, a subdivision of the Callovian Stage within the Middle Jurassic. The Callovian followed the Bathonian and preceded the Oxfordian, representing a major interval in the development of Jurassic marine ecosystems.
During the Callovian, ammonites were abundant and diverse across the seas of Europe. Different lineages evolved rapidly, producing characteristic fossil assemblages that palaeontologists use to divide sedimentary successions into detailed biozones.
Because many ammonite species existed for comparatively restricted intervals but were geographically widespread, they are important index fossils. Their occurrence allows geologists to correlate similarly aged marine rocks exposed in separate regions.
The recorded Middle Callovian age places this specimen within a defined portion of Jurassic time rather than describing it only as a general ammonite fossil.
Jurassic Marine Environment of Switzerland
During the Middle Jurassic, the region now forming northern Switzerland was covered by a warm sea associated with the northern margins of the ancient Tethys Ocean. Shallow marine platforms and deeper channels extended across much of central Europe.
These waters supported ammonites, belemnites, nautiloids, bivalves, gastropods, brachiopods, echinoids, crustaceans, fish and marine reptiles. Carbonate mud, clay, shell debris and iron-rich particles accumulated across the seabed under changing environmental conditions.
The marine deposits around Herznach are particularly notable for their iron-rich character. Slow sedimentation, seabed reworking and chemical processes concentrated iron minerals within some layers, producing the distinctive ferruginous rocks for which the locality became known.
Ammonite shells settling onto this seabed could become surrounded by iron-bearing sediment. This may produce natural brown, reddish, ochre or dark mineral colouring within the fossil or its matrix, adding to the specimen’s characteristic appearance.
Herznach Iron-Ore Geology
Herznach is historically famous for its Jurassic iron-ore deposits and associated fossils. The local sedimentary sequence includes iron-rich beds that were commercially mined during the twentieth century, exposing fossiliferous strata and producing numerous ammonites and other marine specimens.
The iron ore developed within marine sediment through a combination of slow deposition, reworking, mineral concentration and chemical alteration. Rounded iron-rich grains, shell fragments and marine fossils became incorporated into the deposits.
Fossils from Herznach are therefore valued not only for their palaeontological interest but also for their connection with an important Swiss mining and geological heritage. The association of this ammonite with Herznach gives the specimen a distinctive provenance recognised by collectors of European Jurassic fossils.
Natural Fossilisation and Preservation
After the ammonite died, its shell descended to the Jurassic seabed. The soft tissues decomposed, while sediment entered the empty shell chambers and accumulated around the exterior.
As additional layers were deposited, the sediment became compacted and gradually transformed into rock. The ammonite’s original aragonitic shell could dissolve, recrystallise or be replaced by other minerals. Sediment hardened within the chambers, preserving the shell as an internal mould, while surviving exterior material retained elements of the original ornamentation.
Iron-bearing groundwater and sediment could further influence the colour and mineral composition of the fossil. Natural fractures, incomplete edges, weathered areas, matrix deposits, mineral markings and variations in surface detail are authentic products of burial and geological alteration.
These characteristics form part of the specimen’s individual history and ensure that no two fossils are precisely identical.
Actual Specimen and Certificate of Authenticity
This is a genuine fossil specimen and not a cast, replica or artificial reproduction. The listing photographs show the exact Sublunuloceras (Orbignyceras) pseudopunctatum ammonite that will be supplied, allowing you to inspect its shell profile, ornamentation, matrix, mineral colouring and natural preservation before purchasing.
Full sizing is shown in the photographs.
The fossil includes a generic Certificate of Authenticity card carrying a lifetime guarantee. Its elegant oppeliid morphology, Middle Callovian age, documented Herznach provenance and association with Switzerland’s historic Jurassic iron-ore deposits make it an excellent addition to an ammonite collection, European fossil display, natural-history cabinet or educational geological collection.
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