Description
Genuine Proisphyinctes (Leptosphinctes) pseudomartini Ammonite Fossil
This carefully chosen specimen is a genuine Proisphyinctes (Leptosphinctes) pseudomartini ammonite fossil from Caen in Calvados, Normandy, France. It dates from the Bajocian Stage of the Middle Jurassic and represents an extinct marine cephalopod that inhabited the ancient seas of western Europe approximately 168–171 million years ago.
Combining a detailed taxonomic identification with a recognised geological stage and recorded French locality, this ammonite offers excellent geological, educational and collectable interest. It is particularly suitable for collections focused on Jurassic fossils, ammonites, extinct cephalopods, French palaeontology or specimens from historically important European fossil localities.
The photograph shows the exact fossil specimen you will receive. Full sizing and scale information can be seen in the accompanying photograph.
Bajocian Middle Jurassic Geology
The Bajocian is one of the four stages forming the Middle Jurassic Period. Its name derives from Bayeux in Normandy, giving fossils from Calvados a particularly strong connection to the history of Jurassic stratigraphy and palaeontological research.
During the Bajocian, the area now occupied by Normandy lay beneath warm, shallow to moderately deep marine waters. These seas formed part of a wider network of Jurassic marine basins that extended across western Europe. Fine carbonate mud, mineral grains, fragmented shells and the remains of marine organisms accumulated gradually across the seabed.
Continued burial, compaction and natural cementation transformed these sediments into limestone, marl and associated sedimentary rocks. The resulting fossil-bearing strata preserve evidence of a diverse marine ecosystem inhabited by ammonites, belemnites, nautiloids, bivalves, brachiopods, gastropods, echinoids and other invertebrates.
Following the death of the ammonite, its shell settled onto the seabed and became buried by sediment. The original aragonitic shell could later be mineralised, replaced or dissolved, leaving an impression, natural mould or stone-filled representation of its chambered interior. Mineral staining, matrix coverage, surface texture and areas of incomplete preservation are authentic features produced by millions of years of fossilisation and geological change.
Proisphyinctes (Leptosphinctes) pseudomartini Shell Form
This ammonite possessed a planispirally coiled shell, meaning that its successive whorls developed around a central umbilical region within the same plane. The shell displays the elegant spiral geometry characteristic of perisphinctid-style Jurassic ammonites.
The coiling is generally evolute in appearance, with the later whorls only partly overlapping the earlier ones. This leaves a relatively broad and clearly visible umbilicus, allowing much of the ammonite’s growth sequence to remain exposed.
Ornamentation typically consists of radial primary ribs extending outward from the umbilical region across the flanks. These ribs may divide into two secondary branches towards the outer part of the whorl, creating the bifurcating rib pattern frequently associated with this type of Jurassic ammonite. Rib spacing, curvature, division and strength can change during growth and are important features when comparing related ammonite forms.
Depending on its individual preservation, this specimen may show sections of the inner and outer whorls, bifurcating ribs, the open umbilical region, ventral margin, internal chambers or surrounding Jurassic matrix. Its surviving features record both the biological development of the original animal and the geological processes that affected its shell after burial.
Extinct Jurassic Marine Cephalopod
Ammonites were marine molluscs related to living squid, cuttlefish, octopuses and nautiluses. Unlike most modern cephalopods, they possessed a hard external shell divided internally into a succession of chambers.
The animal lived within the final and largest section of the shell, known as the body chamber. The older chambers formed the phragmocone, which contributed to buoyancy control. A narrow connecting structure called the siphuncle passed through these chambers and allowed the ammonite to regulate the proportions of liquid and gas within them.
As the ammonite grew, it constructed progressively larger chambers around the outer edge of its shell. Internal walls called septa separated the chambers. Where the septa joined the outer shell, they produced intricate patterns known as suture lines.
Palaeontologists use shell shape, whorl proportions, umbilical width, rib development and suture patterns when studying and classifying ammonites. Because many ammonite lineages evolved rapidly and became widely distributed through ancient seas, their fossils are valuable for identifying and correlating Jurassic sedimentary rocks.
Caen Ammonite from Normandy, France
Caen and the surrounding Calvados region are internationally recognised for their Jurassic limestone, historic quarries and long record of fossil discovery. The rocks of Normandy provide evidence of the extensive marine environments that covered this region during the Middle Jurassic.
The marine sediments around Caen preserve a variety of fossil organisms and record changing water depths, seabed conditions, sediment supply and biological communities. Ammonites are among the most scientifically informative fossils found in such deposits because their distinctive shell forms can help characterise particular intervals of geological time.
A fossil retaining its taxonomic identification, geological stage and collection locality carries greater scientific and collectable significance than an ammonite without recorded provenance. This Proisphyinctes (Leptosphinctes) pseudomartini would make a distinctive addition to a specialist ammonite collection, geological study cabinet, educational display or collection of French Jurassic fossils.
Actual Specimen with Certificate of Authenticity
This is a genuine fossil specimen and not a cast, replica or reproduction. It has been individually selected for its natural form, geological character and collectable appeal.
The photograph shows the actual Proisphyinctes (Leptosphinctes) pseudomartini ammonite fossil you will receive. Full sizing is shown in the photograph.
A generic Certificate of Authenticity card is included with a lifetime guarantee of authenticity, providing lasting confidence that this is a genuine Middle Jurassic ammonite fossil from Caen, Calvados, Normandy, France.
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