This carefully chosen fossil is a genuine Phymatoceras narbonense ammonite from Deux-Sèvres in the Nouvelle-Aquitaine region of France. Dating from the Upper Toarcian Stage of the Lower Jurassic, it represents an extinct marine cephalopod that lived in the ancient seas of western Europe approximately 174 to 178 million years ago.
The specimen combines a named ammonite species with a documented French locality and important Lower Jurassic age. Its strongly ornamented coiled shell makes it an appealing addition to an ammonite collection, geological display or cabinet of European fossils.
The photograph shows the actual fossil specimen you will receive, allowing its individual coiling, ribbing, preservation, colour, matrix and natural geological characteristics 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.
Scientific name: Phymatoceras narbonense
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Hammatoceratoidea
Family: Phymatoceratidae
Geological period: Jurassic
Epoch: Early Jurassic
Stage: Upper Toarcian
Locality: Deux-Sèvres, Nouvelle-Aquitaine, France
Phymatoceras is a distinctive genus of strongly ornamented ammonites known from the later Toarcian. Members of the genus belong to an important group of Jurassic ammonites characterised by robust shell sculpture, pronounced ribbing and raised tubercles.
Ammonites are especially valuable in palaeontology because their shell forms evolved rapidly and many species were distributed across extensive marine regions. Their fossils allow geologists to compare sedimentary layers, establish relative ages and reconstruct connections between ancient seas.
Phymatoceras narbonense possessed a planispirally coiled shell, with successive whorls growing around a central umbilicus in a single plane. The shell is typically relatively evolute, leaving a substantial portion of the earlier whorls visible within the broad central area.
Strong primary ribs rise near the umbilical margin and extend across the flanks. These ribs may divide or strengthen towards the outer part of the whorl, where prominent tubercles or raised nodes can develop. This bold ornamentation gives Phymatoceras ammonites their characteristic sculptured appearance.
The outer edge of an ammonite shell is known as the venter. Its shape, combined with the style of the ribs, the position of the tubercles and the degree of overlap between successive whorls, provides important diagnostic information when distinguishing related ammonite genera and species.
The strength and visibility of these features vary according to the growth stage and preservation of the individual specimen. Natural surface wear, incomplete areas, mineral deposits, fractures and attached matrix are authentic characteristics created during fossilisation and subsequent geological exposure.
The Toarcian is the final stage of the Lower Jurassic and follows the Pliensbachian. The Upper Toarcian records an interval of considerable ammonite diversity and evolutionary change before the beginning of the Middle Jurassic.
During this time, extensive shallow and moderately deep seas covered much of western Europe. Ammonites were among the most widespread mobile animals within these environments and evolved into numerous distinctive forms.
The surrounding marine ecosystem also contained belemnites, nautiloids, bivalves, brachiopods, gastropods, crinoids and other invertebrates. Fish and marine reptiles occupied higher levels within the food web, while a variety of burrowing and bottom-dwelling organisms inhabited the seabed.
Ammonite assemblages from the Upper Toarcian are used to subdivide the stage into detailed intervals. Changes in species through successive layers help palaeontologists reconstruct evolutionary patterns, sea-level fluctuations and connections between Jurassic marine basins.
Deux-Sèvres lies within Nouvelle-Aquitaine in western France, an area containing extensive Jurassic sedimentary rocks. During the Toarcian, this region formed part of a marine basin connected to the wider seas surrounding the European archipelago and the ancient Tethys Ocean.
Clay, marl, limestone and carbonate-rich sediment accumulated across the seabed. The exact character of these deposits varied with water depth, current strength, oxygen levels and the amount of sediment entering the basin.
Shells and skeletal remains from marine animals became incorporated into these sediments. Under favourable conditions, ammonite shells were buried before being completely destroyed by currents, scavengers or dissolution.
Over geological time, the marine deposits were compacted and cemented into rock. Later uplift and erosion exposed the fossil-bearing layers, allowing their ancient fauna to be studied and collected.
Ammonites were marine molluscs related to living squid, cuttlefish, octopuses and nautiluses. The living animal occupied the final and largest section of its shell, called the body chamber.
The older coiled portion was divided internally into a series of chambers by curved walls known as septa. A narrow tube called the siphuncle connected these chambers and helped regulate the balance of liquid and gas within them. This provided buoyancy control and allowed the ammonite to maintain its position in the water column.
Movement was achieved through jet propulsion. Water was drawn into the mantle cavity and expelled through a muscular funnel, pushing the ammonite in the opposite direction. Tentacles surrounding the mouth were probably used to capture small prey, collect food and explore the surrounding marine environment.
The ribbed and tuberculate shell of Phymatoceras narbonense provided structural reinforcement while recording the animal’s growth. As the ammonite matured, new shell material was added around the aperture and additional chambers formed behind the living animal.
After death, the ammonite shell settled onto the Toarcian seabed. Its soft tissues decayed while sediment accumulated around and within the empty shell. Burial helped protect the remains from complete destruction.
Over millions of years, pressure compacted the surrounding sediment into rock. Mineral-rich groundwater could recrystallise, replace or dissolve the original aragonitic shell material. Sediment filling the chambers hardened into an internal mould that preserved the ammonite’s overall coiling and impressions of its ornamentation.
Natural fractures, matrix attachments, mineral staining, weathered sections and incomplete areas form part of the specimen’s geological history. Each fossil has undergone a unique combination of burial, mineral alteration, tectonic movement and erosion, ensuring that no two specimens are exactly alike.
This Phymatoceras narbonense ammonite is suitable for 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.