Description
Genuine Holcodiscus caillaudianus Ammonite Fossil
This carefully chosen specimen is a genuine Holcodiscus caillaudianus ammonite fossil from Montagne de Lure in Alpes-de-Haute-Provence, France. It dates to the Barremian Stage of the Lower Cretaceous and represents an extinct marine cephalopod that inhabited the ancient seas of southern Europe more than 120 million years ago.
Holcodiscus caillaudianus belongs to the extinct ammonite family Holcodiscidae and the order Ammonitida. It is a particularly attractive Lower Cretaceous ammonite distinguished by its coiled shell, prominent ribbing and periodically strengthened ornament. The species was originally described during the nineteenth century by the French palaeontologist Alcide d’Orbigny and was historically introduced under the name Ammonites caillaudianus.
Ammonites were relatives of modern squid, cuttlefish, octopuses and nautiluses. Their shells were divided internally into a series of chambers, with the living animal occupying the final and largest body chamber. Earlier chambers were connected by a narrow tube called the siphuncle, which helped regulate buoyancy as the ammonite moved through the water.
Holcodiscus Shell Morphology
The shell of Holcodiscus caillaudianus is planispirally coiled, meaning that its successive whorls developed within a single plane. Members of the genus may display whorl sections ranging from rounded to somewhat compressed or rectangular, depending on growth stage and preservation.
The shell ornament typically consists of numerous fine, low ribs that may be straight, gently curved or flexuous. Some ribs remain simple, while others divide as they pass across the shell. At intervals, the finer ornament is interrupted by stronger raised ribs carrying more pronounced swellings or tubercles along the flanks and near the ventrolateral margins.
These enlarged ribs give Holcodiscus a distinctive sculptured appearance and probably strengthened the shell while also affecting water flow around the animal. The inner whorls may be more depressed and strongly rounded, while the later growth stages can become more robustly ornamented.
Depending on the specimen’s preservation, visible features may include the umbilicus, individual whorls, ribbing, tubercles, the ventral margin, areas of body chamber and sections of the chambered phragmocone. Natural fractures, worn ribs, mineral-filled cracks, incomplete margins and attached matrix are normal characteristics of an authentic fossil and form part of its individual geological history.
Life of a Cretaceous Ammonite
During life, Holcodiscus caillaudianus was an active marine animal inhabiting the water column above the seabed. Its chambered shell provided buoyancy, while a muscular body equipped with arms and sensory organs projected from the open end of the shell.
Ammonites were likely opportunistic predators and scavengers. Depending on their size and ecology, they may have consumed small crustaceans, planktonic organisms, juvenile molluscs and other marine animals. Their own predators included fish and marine reptiles, and some ammonite shells preserve damage interpreted as unsuccessful attacks or post-mortem breakage.
The complex sutures visible on some ammonites mark the junctions between internal chamber walls and the outer shell. These folded structures strengthened the shell against water pressure and are important features used by palaeontologists when classifying ammonite groups.
After death, the soft tissues decayed and the shell descended to the seabed. It could then be transported, partially broken or filled with sediment before burial. Over millions of years, mineral-rich water moved through the surrounding deposits, preserving or replacing parts of the original shell and producing the fossil visible today.
Barremian Lower Cretaceous Geology
The Barremian is a stage of the Lower Cretaceous Period and records a time when extensive marine environments covered large areas of what is now south-eastern France. The region formed part of the western Tethyan realm, a broad system of warm seas that supported diverse ammonite faunas.
Sediments in the Montagne de Lure area include limestone, marl and marly limestone deposited within changing marine environments. Fine carbonate mud accumulated on the seabed alongside the shells and skeletal remains of ammonites, belemnites, bivalves, brachiopods, echinoids and other marine organisms.
Local Barremian deposits can vary significantly in thickness and character. Some horizons record quieter offshore sedimentation, while others include harder carbonate beds, glauconitic layers, condensed deposits and surfaces representing interruptions in normal sediment accumulation.
Ammonites are especially valuable for interpreting Lower Cretaceous rocks because many species evolved rapidly and had broad geographical distributions. Their changing assemblages allow separate sedimentary sequences to be compared and placed within detailed relative timescales.
Montagne de Lure, Provence
Montagne de Lure is situated in Alpes-de-Haute-Provence in south-eastern France. The mountain lies within a region renowned for its extensive Mesozoic sedimentary rocks and internationally important Lower Cretaceous ammonite localities.
During the Barremian, this mountainous landscape did not exist in its present form. The area was submerged beneath the Tethyan sea, where marine sediment accumulated over the remains of organisms living within the water and upon the seabed. Later uplift and erosion associated with the development of the Alpine region exposed these ancient deposits.
Fossils from Montagne de Lure are valued for their precise French provenance and their association with classic Lower Cretaceous geology. This specimen is particularly suitable for collectors interested in Barremian ammonites, French fossils, Tethyan marine life, Lower Cretaceous palaeontology or historic European fossil localities.
Authentic Fossil with Certificate of Authenticity
This is a genuine natural fossil and not a replica, cast or manufactured reproduction. Its coiled form, ornamentation, colour and preservation result from the original ammonite shell and the natural processes of burial, mineralisation and geological weathering.
The photograph shows the actual carefully chosen specimen you will receive. Please examine the supplied images closely, as they provide the best record of its precise condition, preserved ribbing, matrix and individual appearance.
Full sizing please see photo.
The fossil includes a generic Certificate of Authenticity card supported by our lifetime guarantee of authenticity. It would make a distinctive addition to an ammonite collection, Cretaceous fossil display, geological cabinet, educational collection or natural-history exhibit.
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