Description
Genuine Bradogarantiana dichotoma Ammonite Fossil
This carefully chosen specimen is a genuine Bradogarantiana dichotoma ammonite fossil from Calvados in Normandy, France. Dating from the Bajocian Stage of the Middle Jurassic, it represents an extinct marine cephalopod that lived in the warm seas covering western Europe approximately 168–171 million years ago.
Its identified species, recognised Middle Jurassic age and recorded Normandy locality give this fossil excellent geological, educational and collectable interest. It would make a distinctive addition to a collection of ammonites, French fossils, Jurassic marine life or natural-history specimens with documented provenance.
The photograph shows the actual 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. It takes its name from Bayeux in Normandy, making ammonites from Calvados especially relevant to the history and scientific study of this geological interval.
During the Bajocian, much of the region now forming north-western France lay beneath a warm, shallow to moderately deep sea. These waters formed part of an extensive network of marine basins spreading across western Europe. Fine carbonate mud, mineral particles, broken shells and the remains of marine organisms accumulated across the seabed.
As these sediments became buried, they were gradually compacted and cemented into limestone, marl and related sedimentary rocks. The Bajocian seas supported a varied ecosystem that included ammonites, nautiloids, belemnites, bivalves, brachiopods, gastropods, echinoids and numerous other invertebrates.
When an ammonite died, its shell could sink to the seabed and become covered by sediment. The original shell material might later be mineralised, replaced or dissolved, leaving an impression, natural mould or stone-filled representation of its chambered interior. The fossil’s colouring, matrix, texture and degree of completeness were shaped by burial conditions, groundwater chemistry, geological pressure and later weathering.
Bradogarantiana dichotoma Shell Characteristics
Bradogarantiana dichotoma possessed a planispirally coiled shell, with each new whorl developing around a central umbilical region within the same plane. Its form belongs to the strongly ornamented ammonite traditions characteristic of many Bajocian cephalopods.
The shell is generally evolute in appearance, meaning that a significant portion of the earlier whorls remains visible rather than being concealed by later growth. This creates a relatively open umbilicus and allows the spiral development of the ammonite to be clearly appreciated.
Ornamentation includes numerous radial ribs extending across the shell flanks. The species name “dichotoma” reflects the divided or branching character associated with the rib pattern. Primary ribs may originate around the inner part of the whorl before dividing into secondary ribs towards the outer flank. The density, curvature and division of these ribs contribute to the fossil’s distinctive sculptured appearance.
Depending on its individual preservation, this specimen may display sections of the inner and outer whorls, branching ribs, the umbilical region, outer margin, internal chambers or surrounding Jurassic matrix. Variations in surface texture, matrix coverage, mineral staining and completeness are genuine features produced during fossilisation.
An 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 living animal occupied the final and largest section, known as the body chamber. The earlier chambers formed the phragmocone, which played an important role in buoyancy control. A narrow connecting structure called the siphuncle passed through the chambers and allowed the ammonite to regulate the proportions of liquid and gas within them.
As the animal grew, it added progressively larger chambers around the outside of its shell. The internal partitions separating these chambers are called septa. Where the septa met the shell wall, they created complex patterns known as suture lines.
Shell shape, ribbing, whorl proportions, umbilical width, ventral form and suture patterns are among the features palaeontologists use when identifying ammonite fossils. Because ammonites evolved rapidly and were widely distributed through ancient seas, they are also important index fossils used to compare and date sedimentary rock layers.
Calvados Ammonite from Normandy, France
Calvados is internationally recognised for its Jurassic geology and long history of fossil study. The fossil-bearing rocks of Normandy preserve evidence of changing sea levels, marine environments and biological communities during the Jurassic Period.
The connection between the Bajocian and Bayeux gives fossils from this part of France particular historical interest. Ammonites collected from Normandy have contributed greatly to the understanding and subdivision of Middle Jurassic strata.
A fossil retaining its species identification, geological stage and collection locality offers greater scientific and collectable significance than an ammonite without recorded provenance. This Bradogarantiana dichotoma would suit a specialist ammonite collection, geological study cabinet, educational display or collection of unusual 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 appearance, geological character and collectable appeal.
The photograph shows the exact Bradogarantiana dichotoma 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 Bajocian ammonite fossil from the Middle Jurassic of Normandy, France.
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