Description
Rare Siemiradzkia matisconensis Ammonite with Lappets
This carefully chosen fossil is a rare and genuine Siemiradzkia matisconensis ammonite preserving distinctive lappets at the aperture. It originates from Saint-Benin-d’Azy in the Nièvre department of Bourgogne-Franche-Comté, France, and dates from the Lower Bathonian Stage of the Middle Jurassic.
The survival of the delicate apertural lappets makes this an especially interesting example. These projecting structures formed part of the mature shell opening and are often lost through breakage, erosion or incomplete fossilisation. Their presence provides evidence that the ammonite had reached its adult growth stage before death.
The photograph shows the actual fossil specimen you will receive, allowing its individual coiling, ribbing, lappets, preservation, colour, matrix and natural geological features to be examined before purchase. Full sizing and proportions can be seen in the accompanying photograph.
This authentic fossil includes a generic Certificate of Authenticity card with a lifetime guarantee.
Fossil Classification and Geological Details
Scientific name: Siemiradzkia matisconensis
Fossil type: Ammonite
Notable feature: Preserved apertural lappets
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Suborder: Ammonitina
Superfamily: Perisphinctoidea
Family: Perisphinctidae
Geological period: Jurassic
Epoch: Middle Jurassic
Stage: Lower Bathonian
Locality: Saint-Benin-d’Azy, Nièvre, Bourgogne-Franche-Comté, France
Siemiradzkia belongs to the Perisphinctidae, an important family of Jurassic ammonites recognised for their evolute coiling and prominently ribbed shells. Members of this family were widespread in Middle and Late Jurassic seas and are valuable for identifying and correlating marine sedimentary rocks.
Preserved Lappets and Mature Aperture
Lappets are paired projections extending forwards from either side of the mature aperture. They developed only when the ammonite reached adulthood and ceased normal shell enlargement. Their precise biological function remains uncertain, although they may have helped protect or support the animal’s soft body around the shell opening.
Within many perisphinctid ammonite lineages, lappet-bearing forms are interpreted as microconchs. Microconchs are the smaller members of sexually dimorphic ammonite pairs and are generally considered to represent males, while the larger, usually simple-apertured macroconchs are interpreted as females.
The preserved lappets therefore add significant palaeontological interest. They help demonstrate that the specimen represents a mature individual rather than merely a small juvenile ammonite. Because these structures are thin and project beyond the main shell, examples retaining visible lappets are particularly desirable among specialist collectors.
Siemiradzkia Shell Morphology
Siemiradzkia matisconensis possessed a planispirally coiled and relatively evolute shell. In an evolute ammonite, the outer whorls overlap the earlier coils only slightly, leaving a broad central umbilicus and much of the inner growth visible.
The flanks are ornamented with clearly developed ribs that begin close to the umbilical margin. These primary ribs commonly divide into two or more secondary branches as they cross the flanks and continue towards the venter, the outermost edge of the shell. This repeated rib pattern created a sculptured surface while also strengthening the shell.
The lappets project from the mature aperture and provide a dramatic finishing feature to the final body chamber. The strength of the ribbing, completeness of the whorls and visibility of the aperture vary naturally according to preservation.
Any surface wear, mineral staining, attached matrix, incomplete areas or natural fractures are genuine geological features resulting from burial, fossilisation and subsequent exposure.
Lower Bathonian Marine Life
The Bathonian is one of the four principal stages of the Middle Jurassic, following the Bajocian and preceding the Callovian. The Lower Bathonian represents the earliest part of this stage and records an interval when extensive shallow seas covered large areas of Europe.
Ammonites were among the most diverse and abundant mobile animals inhabiting these marine environments. Their rapid evolutionary changes and wide geographical distribution make them important index fossils. Particular ammonite assemblages allow palaeontologists to compare rock layers and reconstruct the sequence of events within Middle Jurassic time.
The seas inhabited by Siemiradzkia also supported belemnites, nautiloids, bivalves, brachiopods, gastropods, echinoids, crinoids and many other invertebrates. Predatory marine reptiles and fishes occupied higher levels within the same ecosystem.
Jurassic Geology of Saint-Benin-d’Azy
Saint-Benin-d’Azy lies near Nevers in the Nièvre department of central France. The surrounding district is noted for exposures of fossil-bearing Middle Jurassic limestone, marl and related marine sedimentary rocks.
During the Bathonian, this part of France lay beneath a warm epicontinental sea connected to the broader marine systems surrounding the European archipelago and the ancient Tethys Ocean. Carbonate mud and the remains of marine organisms accumulated across the seabed, eventually becoming limestone and marl.
Conditions varied through time as sea level, water depth, sediment supply and currents changed. Some deposits formed in relatively open marine settings, while others accumulated across shallower carbonate platforms. The ammonites preserved in these rocks provide important evidence for dating the strata and interpreting the ancient environment.
The Nièvre region is well known for its diverse Bathonian ammonite assemblages, particularly representatives of the Perisphinctidae and other characteristic Middle Jurassic families.
Life of a Jurassic Ammonite
Ammonites were extinct marine cephalopods related to living squid, cuttlefish, octopuses and nautiluses. The animal occupied the final and largest section of its shell, known as the body chamber.
The older part of the shell was divided into chambers by curved walls called septa. A narrow tube known as the siphuncle passed through these chambers and allowed the ammonite to regulate their liquid and gas content. This system provided buoyancy control and helped the animal maintain its position in the water.
Movement was achieved through jet propulsion. Water was drawn into the mantle cavity and forcefully expelled through a muscular funnel. Tentacles around the mouth were probably used to capture small prey, gather food and investigate the surrounding environment.
As the ammonite grew, new shell material was added around the aperture. On reaching maturity, growth changed and the paired lappets developed as part of the completed adult opening.
Natural Fossilisation and Preservation
After death, the ammonite settled onto the Jurassic seabed. Its soft tissues decayed while sediment entered and covered the shell. Burial protected part of the specimen from currents, scavengers and physical destruction.
Over millions of years, pressure compacted the sediment and mineral-rich groundwater altered the original aragonitic shell. Shell material could recrystallise, dissolve or be replaced by other minerals. Sediment filling the chambers hardened into an internal mould that preserved the coiled form and rib pattern.
The preservation of apertural lappets required favourable burial conditions because these projecting structures were vulnerable to damage. Their survival gives this fossil additional scientific, visual and collectable appeal.
This rare Siemiradzkia matisconensis ammonite is suitable for specialist fossil collectors, ammonite enthusiasts, geology students and educational natural-history displays. The photograph shows the exact carefully selected specimen you will receive. Full sizing is shown in the photo. A generic Certificate of Authenticity card with a lifetime guarantee is included.
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